The PCRE library is a set of functions that implement regular expres-
sion pattern matching using the same syntax and semantics as Perl, with
- just a few differences. (Certain features that appeared in Python and
+ just a few differences. Certain features that appeared in Python and
PCRE before they appeared in Perl are also available using the Python
- syntax.)
+ syntax. There is also some support for certain .NET and Oniguruma syn-
+ tax items, and there is an option for requesting some minor changes
+ that give better JavaScript compatibility.
The current implementation of PCRE (release 7.x) corresponds approxi-
mately with Perl 5.10, including support for UTF-8 encoded strings and
REVISION
- Last updated: 09 August 2007
- Copyright (c) 1997-2007 University of Cambridge.
+ Last updated: 12 April 2008
+ Copyright (c) 1997-2008 University of Cambridge.
------------------------------------------------------------------------------
Note that libreadline is GPL-licenced, so if you distribute a binary of
pcretest linked in this way, there may be licensing issues.
+ Setting this option causes the -lreadline option to be added to the
+ pcretest build. In many operating environments with a sytem-installed
+ libreadline this is sufficient. However, in some environments (e.g. if
+ an unmodified distribution version of readline is in use), some extra
+ configuration may be necessary. The INSTALL file for libreadline says
+ this:
+
+ "Readline uses the termcap functions, but does not link with the
+ termcap or curses library itself, allowing applications which link
+ with readline the to choose an appropriate library."
+
+ If your environment has not been set up so that an appropriate library
+ is automatically included, you may need to add something like
+
+ LIBS="-ncurses"
+
+ immediately before the configure command.
+
SEE ALSO
REVISION
- Last updated: 18 December 2007
- Copyright (c) 1997-2007 University of Cambridge.
+ Last updated: 13 April 2008
+ Copyright (c) 1997-2008 University of Cambridge.
------------------------------------------------------------------------------
tive algorithm moves through the subject string one character at a
time, for all active paths through the tree.
- 8. None of the backtracking control verbs such as (*PRUNE) are sup-
- ported.
+ 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
+ are not supported. (*FAIL) is supported, and behaves like a failing
+ negative assertion.
ADVANTAGES OF THE ALTERNATIVE ALGORITHM
- Using the alternative matching algorithm provides the following advan-
+ Using the alternative matching algorithm provides the following advan-
tages:
1. All possible matches (at a single point in the subject) are automat-
- ically found, and in particular, the longest match is found. To find
+ ically found, and in particular, the longest match is found. To find
more than one match using the standard algorithm, you have to do kludgy
things with callouts.
- 2. There is much better support for partial matching. The restrictions
- on the content of the pattern that apply when using the standard algo-
- rithm for partial matching do not apply to the alternative algorithm.
- For non-anchored patterns, the starting position of a partial match is
+ 2. There is much better support for partial matching. The restrictions
+ on the content of the pattern that apply when using the standard algo-
+ rithm for partial matching do not apply to the alternative algorithm.
+ For non-anchored patterns, the starting position of a partial match is
available.
- 3. Because the alternative algorithm scans the subject string just
- once, and never needs to backtrack, it is possible to pass very long
- subject strings to the matching function in several pieces, checking
+ 3. Because the alternative algorithm scans the subject string just
+ once, and never needs to backtrack, it is possible to pass very long
+ subject strings to the matching function in several pieces, checking
for partial matching each time.
The alternative algorithm suffers from a number of disadvantages:
- 1. It is substantially slower than the standard algorithm. This is
- partly because it has to search for all possible matches, but is also
+ 1. It is substantially slower than the standard algorithm. This is
+ partly because it has to search for all possible matches, but is also
because it is less susceptible to optimization.
2. Capturing parentheses and back references are not supported.
REVISION
- Last updated: 08 August 2007
- Copyright (c) 1997-2007 University of Cambridge.
+ Last updated: 19 April 2008
+ Copyright (c) 1997-2008 University of Cambridge.
------------------------------------------------------------------------------
before or at the first newline in the subject string, though the
matched text may continue over the newline.
+ PCRE_JAVASCRIPT_COMPAT
+
+ If this option is set, PCRE's behaviour is changed in some ways so that
+ it is compatible with JavaScript rather than Perl. The changes are as
+ follows:
+
+ (1) A lone closing square bracket in a pattern causes a compile-time
+ error, because this is illegal in JavaScript (by default it is treated
+ as a data character). Thus, the pattern AB]CD becomes illegal when this
+ option is set.
+
+ (2) At run time, a back reference to an unset subpattern group matches
+ an empty string (by default this causes the current matching alterna-
+ tive to fail). A pattern such as (\1)(a) succeeds when this option is
+ set (assuming it can find an "a" in the subject), whereas it fails by
+ default, for Perl compatibility.
+
PCRE_MULTILINE
- By default, PCRE treats the subject string as consisting of a single
- line of characters (even if it actually contains newlines). The "start
- of line" metacharacter (^) matches only at the start of the string,
- while the "end of line" metacharacter ($) matches only at the end of
+ By default, PCRE treats the subject string as consisting of a single
+ line of characters (even if it actually contains newlines). The "start
+ of line" metacharacter (^) matches only at the start of the string,
+ while the "end of line" metacharacter ($) matches only at the end of
the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
is set). This is the same as Perl.
- When PCRE_MULTILINE it is set, the "start of line" and "end of line"
- constructs match immediately following or immediately before internal
- newlines in the subject string, respectively, as well as at the very
- start and end. This is equivalent to Perl's /m option, and it can be
+ When PCRE_MULTILINE it is set, the "start of line" and "end of line"
+ constructs match immediately following or immediately before internal
+ newlines in the subject string, respectively, as well as at the very
+ start and end. This is equivalent to Perl's /m option, and it can be
changed within a pattern by a (?m) option setting. If there are no new-
- lines in a subject string, or no occurrences of ^ or $ in a pattern,
+ lines in a subject string, or no occurrences of ^ or $ in a pattern,
setting PCRE_MULTILINE has no effect.
PCRE_NEWLINE_CR
PCRE_NEWLINE_ANYCRLF
PCRE_NEWLINE_ANY
- These options override the default newline definition that was chosen
- when PCRE was built. Setting the first or the second specifies that a
- newline is indicated by a single character (CR or LF, respectively).
- Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
- two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
+ These options override the default newline definition that was chosen
+ when PCRE was built. Setting the first or the second specifies that a
+ newline is indicated by a single character (CR or LF, respectively).
+ Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
+ two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies
that any of the three preceding sequences should be recognized. Setting
- PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
+ PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be
recognized. The Unicode newline sequences are the three just mentioned,
- plus the single characters VT (vertical tab, U+000B), FF (formfeed,
- U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
- (paragraph separator, U+2029). The last two are recognized only in
+ plus the single characters VT (vertical tab, U+000B), FF (formfeed,
+ U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
+ (paragraph separator, U+2029). The last two are recognized only in
UTF-8 mode.
- The newline setting in the options word uses three bits that are
+ The newline setting in the options word uses three bits that are
treated as a number, giving eight possibilities. Currently only six are
- used (default plus the five values above). This means that if you set
- more than one newline option, the combination may or may not be sensi-
+ used (default plus the five values above). This means that if you set
+ more than one newline option, the combination may or may not be sensi-
ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
- PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
+ PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and
cause an error.
- The only time that a line break is specially recognized when compiling
- a pattern is if PCRE_EXTENDED is set, and an unescaped # outside a
- character class is encountered. This indicates a comment that lasts
- until after the next line break sequence. In other circumstances, line
- break sequences are treated as literal data, except that in
+ The only time that a line break is specially recognized when compiling
+ a pattern is if PCRE_EXTENDED is set, and an unescaped # outside a
+ character class is encountered. This indicates a comment that lasts
+ until after the next line break sequence. In other circumstances, line
+ break sequences are treated as literal data, except that in
PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
and are therefore ignored.
The newline option that is set at compile time becomes the default that
- is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
+ is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
PCRE_NO_AUTO_CAPTURE
If this option is set, it disables the use of numbered capturing paren-
- theses in the pattern. Any opening parenthesis that is not followed by
- ? behaves as if it were followed by ?: but named parentheses can still
- be used for capturing (and they acquire numbers in the usual way).
+ theses in the pattern. Any opening parenthesis that is not followed by
+ ? behaves as if it were followed by ?: but named parentheses can still
+ be used for capturing (and they acquire numbers in the usual way).
There is no equivalent of this option in Perl.
PCRE_UNGREEDY
- This option inverts the "greediness" of the quantifiers so that they
- are not greedy by default, but become greedy if followed by "?". It is
- not compatible with Perl. It can also be set by a (?U) option setting
+ This option inverts the "greediness" of the quantifiers so that they
+ are not greedy by default, but become greedy if followed by "?". It is
+ not compatible with Perl. It can also be set by a (?U) option setting
within the pattern.
PCRE_UTF8
- This option causes PCRE to regard both the pattern and the subject as
- strings of UTF-8 characters instead of single-byte character strings.
- However, it is available only when PCRE is built to include UTF-8 sup-
- port. If not, the use of this option provokes an error. Details of how
- this option changes the behaviour of PCRE are given in the section on
+ This option causes PCRE to regard both the pattern and the subject as
+ strings of UTF-8 characters instead of single-byte character strings.
+ However, it is available only when PCRE is built to include UTF-8 sup-
+ port. If not, the use of this option provokes an error. Details of how
+ this option changes the behaviour of PCRE are given in the section on
UTF-8 support in the main pcre page.
PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
- automatically checked. There is a discussion about the validity of
- UTF-8 strings in the main pcre page. If an invalid UTF-8 sequence of
- bytes is found, pcre_compile() returns an error. If you already know
+ automatically checked. There is a discussion about the validity of
+ UTF-8 strings in the main pcre page. If an invalid UTF-8 sequence of
+ bytes is found, pcre_compile() returns an error. If you already know
that your pattern is valid, and you want to skip this check for perfor-
- mance reasons, you can set the PCRE_NO_UTF8_CHECK option. When it is
- set, the effect of passing an invalid UTF-8 string as a pattern is
- undefined. It may cause your program to crash. Note that this option
- can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
+ mance reasons, you can set the PCRE_NO_UTF8_CHECK option. When it is
+ set, the effect of passing an invalid UTF-8 string as a pattern is
+ undefined. It may cause your program to crash. Note that this option
+ can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
UTF-8 validity checking of subject strings.
COMPILATION ERROR CODES
- The following table lists the error codes than may be returned by
- pcre_compile2(), along with the error messages that may be returned by
- both compiling functions. As PCRE has developed, some error codes have
+ The following table lists the error codes than may be returned by
+ pcre_compile2(), along with the error messages that may be returned by
+ both compiling functions. As PCRE has developed, some error codes have
fallen out of use. To avoid confusion, they have not been re-used.
0 no error
50 [this code is not in use]
51 octal value is greater than \377 (not in UTF-8 mode)
52 internal error: overran compiling workspace
- 53 internal error: previously-checked referenced subpattern not
+ 53 internal error: previously-checked referenced subpattern not
found
54 DEFINE group contains more than one branch
55 repeating a DEFINE group is not allowed
56 inconsistent NEWLINE options
- 57 \g is not followed by a braced name or an optionally braced
- non-zero number
- 58 (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
+ 57 \g is not followed by a braced, angle-bracketed, or quoted
+ name/number or by a plain number
+ 58 a numbered reference must not be zero
59 (*VERB) with an argument is not supported
60 (*VERB) not recognized
61 number is too big
62 subpattern name expected
63 digit expected after (?+
+ 64 ] is an invalid data character in JavaScript compatibility mode
- The numbers 32 and 10000 in errors 48 and 49 are defaults; different
+ The numbers 32 and 10000 in errors 48 and 49 are defaults; different
values may be used if the limits were changed when PCRE was built.
pcre_extra *pcre_study(const pcre *code, int options
const char **errptr);
- If a compiled pattern is going to be used several times, it is worth
+ If a compiled pattern is going to be used several times, it is worth
spending more time analyzing it in order to speed up the time taken for
- matching. The function pcre_study() takes a pointer to a compiled pat-
+ matching. The function pcre_study() takes a pointer to a compiled pat-
tern as its first argument. If studying the pattern produces additional
- information that will help speed up matching, pcre_study() returns a
- pointer to a pcre_extra block, in which the study_data field points to
+ information that will help speed up matching, pcre_study() returns a
+ pointer to a pcre_extra block, in which the study_data field points to
the results of the study.
The returned value from pcre_study() can be passed directly to
- pcre_exec(). However, a pcre_extra block also contains other fields
- that can be set by the caller before the block is passed; these are
+ pcre_exec(). However, a pcre_extra block also contains other fields
+ that can be set by the caller before the block is passed; these are
described below in the section on matching a pattern.
- If studying the pattern does not produce any additional information
+ If studying the pattern does not produce any additional information
pcre_study() returns NULL. In that circumstance, if the calling program
- wants to pass any of the other fields to pcre_exec(), it must set up
+ wants to pass any of the other fields to pcre_exec(), it must set up
its own pcre_extra block.
- The second argument of pcre_study() contains option bits. At present,
+ The second argument of pcre_study() contains option bits. At present,
no options are defined, and this argument should always be zero.
- The third argument for pcre_study() is a pointer for an error message.
- If studying succeeds (even if no data is returned), the variable it
- points to is set to NULL. Otherwise it is set to point to a textual
+ The third argument for pcre_study() is a pointer for an error message.
+ If studying succeeds (even if no data is returned), the variable it
+ points to is set to NULL. Otherwise it is set to point to a textual
error message. This is a static string that is part of the library. You
- must not try to free it. You should test the error pointer for NULL
+ must not try to free it. You should test the error pointer for NULL
after calling pcre_study(), to be sure that it has run successfully.
This is a typical call to pcre_study():
&error); /* set to NULL or points to a message */
At present, studying a pattern is useful only for non-anchored patterns
- that do not have a single fixed starting character. A bitmap of possi-
+ that do not have a single fixed starting character. A bitmap of possi-
ble starting bytes is created.
LOCALE SUPPORT
- PCRE handles caseless matching, and determines whether characters are
- letters, digits, or whatever, by reference to a set of tables, indexed
- by character value. When running in UTF-8 mode, this applies only to
- characters with codes less than 128. Higher-valued codes never match
- escapes such as \w or \d, but can be tested with \p if PCRE is built
- with Unicode character property support. The use of locales with Uni-
- code is discouraged. If you are handling characters with codes greater
- than 128, you should either use UTF-8 and Unicode, or use locales, but
+ PCRE handles caseless matching, and determines whether characters are
+ letters, digits, or whatever, by reference to a set of tables, indexed
+ by character value. When running in UTF-8 mode, this applies only to
+ characters with codes less than 128. Higher-valued codes never match
+ escapes such as \w or \d, but can be tested with \p if PCRE is built
+ with Unicode character property support. The use of locales with Uni-
+ code is discouraged. If you are handling characters with codes greater
+ than 128, you should either use UTF-8 and Unicode, or use locales, but
not try to mix the two.
- PCRE contains an internal set of tables that are used when the final
- argument of pcre_compile() is NULL. These are sufficient for many
+ PCRE contains an internal set of tables that are used when the final
+ argument of pcre_compile() is NULL. These are sufficient for many
applications. Normally, the internal tables recognize only ASCII char-
acters. However, when PCRE is built, it is possible to cause the inter-
nal tables to be rebuilt in the default "C" locale of the local system,
which may cause them to be different.
- The internal tables can always be overridden by tables supplied by the
+ The internal tables can always be overridden by tables supplied by the
application that calls PCRE. These may be created in a different locale
- from the default. As more and more applications change to using Uni-
+ from the default. As more and more applications change to using Uni-
code, the need for this locale support is expected to die away.
- External tables are built by calling the pcre_maketables() function,
- which has no arguments, in the relevant locale. The result can then be
- passed to pcre_compile() or pcre_exec() as often as necessary. For
- example, to build and use tables that are appropriate for the French
- locale (where accented characters with values greater than 128 are
+ External tables are built by calling the pcre_maketables() function,
+ which has no arguments, in the relevant locale. The result can then be
+ passed to pcre_compile() or pcre_exec() as often as necessary. For
+ example, to build and use tables that are appropriate for the French
+ locale (where accented characters with values greater than 128 are
treated as letters), the following code could be used:
setlocale(LC_CTYPE, "fr_FR");
tables = pcre_maketables();
re = pcre_compile(..., tables);
- The locale name "fr_FR" is used on Linux and other Unix-like systems;
+ The locale name "fr_FR" is used on Linux and other Unix-like systems;
if you are using Windows, the name for the French locale is "french".
- When pcre_maketables() runs, the tables are built in memory that is
- obtained via pcre_malloc. It is the caller's responsibility to ensure
- that the memory containing the tables remains available for as long as
+ When pcre_maketables() runs, the tables are built in memory that is
+ obtained via pcre_malloc. It is the caller's responsibility to ensure
+ that the memory containing the tables remains available for as long as
it is needed.
The pointer that is passed to pcre_compile() is saved with the compiled
- pattern, and the same tables are used via this pointer by pcre_study()
+ pattern, and the same tables are used via this pointer by pcre_study()
and normally also by pcre_exec(). Thus, by default, for any single pat-
tern, compilation, studying and matching all happen in the same locale,
but different patterns can be compiled in different locales.
- It is possible to pass a table pointer or NULL (indicating the use of
- the internal tables) to pcre_exec(). Although not intended for this
- purpose, this facility could be used to match a pattern in a different
+ It is possible to pass a table pointer or NULL (indicating the use of
+ the internal tables) to pcre_exec(). Although not intended for this
+ purpose, this facility could be used to match a pattern in a different
locale from the one in which it was compiled. Passing table pointers at
run time is discussed below in the section on matching a pattern.
int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
int what, void *where);
- The pcre_fullinfo() function returns information about a compiled pat-
+ The pcre_fullinfo() function returns information about a compiled pat-
tern. It replaces the obsolete pcre_info() function, which is neverthe-
less retained for backwards compability (and is documented below).
- The first argument for pcre_fullinfo() is a pointer to the compiled
- pattern. The second argument is the result of pcre_study(), or NULL if
- the pattern was not studied. The third argument specifies which piece
- of information is required, and the fourth argument is a pointer to a
- variable to receive the data. The yield of the function is zero for
+ The first argument for pcre_fullinfo() is a pointer to the compiled
+ pattern. The second argument is the result of pcre_study(), or NULL if
+ the pattern was not studied. The third argument specifies which piece
+ of information is required, and the fourth argument is a pointer to a
+ variable to receive the data. The yield of the function is zero for
success, or one of the following negative numbers:
PCRE_ERROR_NULL the argument code was NULL
PCRE_ERROR_BADMAGIC the "magic number" was not found
PCRE_ERROR_BADOPTION the value of what was invalid
- The "magic number" is placed at the start of each compiled pattern as
- an simple check against passing an arbitrary memory pointer. Here is a
- typical call of pcre_fullinfo(), to obtain the length of the compiled
+ The "magic number" is placed at the start of each compiled pattern as
+ an simple check against passing an arbitrary memory pointer. Here is a
+ typical call of pcre_fullinfo(), to obtain the length of the compiled
pattern:
int rc;
PCRE_INFO_SIZE, /* what is required */
&length); /* where to put the data */
- The possible values for the third argument are defined in pcre.h, and
+ The possible values for the third argument are defined in pcre.h, and
are as follows:
PCRE_INFO_BACKREFMAX
- Return the number of the highest back reference in the pattern. The
- fourth argument should point to an int variable. Zero is returned if
+ Return the number of the highest back reference in the pattern. The
+ fourth argument should point to an int variable. Zero is returned if
there are no back references.
PCRE_INFO_CAPTURECOUNT
- Return the number of capturing subpatterns in the pattern. The fourth
+ Return the number of capturing subpatterns in the pattern. The fourth
argument should point to an int variable.
PCRE_INFO_DEFAULT_TABLES
- Return a pointer to the internal default character tables within PCRE.
- The fourth argument should point to an unsigned char * variable. This
+ Return a pointer to the internal default character tables within PCRE.
+ The fourth argument should point to an unsigned char * variable. This
information call is provided for internal use by the pcre_study() func-
- tion. External callers can cause PCRE to use its internal tables by
+ tion. External callers can cause PCRE to use its internal tables by
passing a NULL table pointer.
PCRE_INFO_FIRSTBYTE
- Return information about the first byte of any matched string, for a
- non-anchored pattern. The fourth argument should point to an int vari-
- able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
+ Return information about the first byte of any matched string, for a
+ non-anchored pattern. The fourth argument should point to an int vari-
+ able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
is still recognized for backwards compatibility.)
- If there is a fixed first byte, for example, from a pattern such as
+ If there is a fixed first byte, for example, from a pattern such as
(cat|cow|coyote), its value is returned. Otherwise, if either
- (a) the pattern was compiled with the PCRE_MULTILINE option, and every
+ (a) the pattern was compiled with the PCRE_MULTILINE option, and every
branch starts with "^", or
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
set (if it were set, the pattern would be anchored),
- -1 is returned, indicating that the pattern matches only at the start
- of a subject string or after any newline within the string. Otherwise
+ -1 is returned, indicating that the pattern matches only at the start
+ of a subject string or after any newline within the string. Otherwise
-2 is returned. For anchored patterns, -2 is returned.
PCRE_INFO_FIRSTTABLE
- If the pattern was studied, and this resulted in the construction of a
+ If the pattern was studied, and this resulted in the construction of a
256-bit table indicating a fixed set of bytes for the first byte in any
- matching string, a pointer to the table is returned. Otherwise NULL is
- returned. The fourth argument should point to an unsigned char * vari-
+ matching string, a pointer to the table is returned. Otherwise NULL is
+ returned. The fourth argument should point to an unsigned char * vari-
able.
PCRE_INFO_HASCRORLF
- Return 1 if the pattern contains any explicit matches for CR or LF
- characters, otherwise 0. The fourth argument should point to an int
- variable. An explicit match is either a literal CR or LF character, or
+ Return 1 if the pattern contains any explicit matches for CR or LF
+ characters, otherwise 0. The fourth argument should point to an int
+ variable. An explicit match is either a literal CR or LF character, or
\r or \n.
PCRE_INFO_JCHANGED
- Return 1 if the (?J) or (?-J) option setting is used in the pattern,
- otherwise 0. The fourth argument should point to an int variable. (?J)
+ Return 1 if the (?J) or (?-J) option setting is used in the pattern,
+ otherwise 0. The fourth argument should point to an int variable. (?J)
and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
PCRE_INFO_LASTLITERAL
- Return the value of the rightmost literal byte that must exist in any
- matched string, other than at its start, if such a byte has been
+ Return the value of the rightmost literal byte that must exist in any
+ matched string, other than at its start, if such a byte has been
recorded. The fourth argument should point to an int variable. If there
- is no such byte, -1 is returned. For anchored patterns, a last literal
- byte is recorded only if it follows something of variable length. For
+ is no such byte, -1 is returned. For anchored patterns, a last literal
+ byte is recorded only if it follows something of variable length. For
example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
/^a\dz\d/ the returned value is -1.
PCRE_INFO_NAMEENTRYSIZE
PCRE_INFO_NAMETABLE
- PCRE supports the use of named as well as numbered capturing parenthe-
- ses. The names are just an additional way of identifying the parenthe-
+ PCRE supports the use of named as well as numbered capturing parenthe-
+ ses. The names are just an additional way of identifying the parenthe-
ses, which still acquire numbers. Several convenience functions such as
- pcre_get_named_substring() are provided for extracting captured sub-
- strings by name. It is also possible to extract the data directly, by
- first converting the name to a number in order to access the correct
+ pcre_get_named_substring() are provided for extracting captured sub-
+ strings by name. It is also possible to extract the data directly, by
+ first converting the name to a number in order to access the correct
pointers in the output vector (described with pcre_exec() below). To do
- the conversion, you need to use the name-to-number map, which is
+ the conversion, you need to use the name-to-number map, which is
described by these three values.
The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
- of each entry; both of these return an int value. The entry size
- depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
- a pointer to the first entry of the table (a pointer to char). The
+ of each entry; both of these return an int value. The entry size
+ depends on the length of the longest name. PCRE_INFO_NAMETABLE returns
+ a pointer to the first entry of the table (a pointer to char). The
first two bytes of each entry are the number of the capturing parenthe-
- sis, most significant byte first. The rest of the entry is the corre-
- sponding name, zero terminated. The names are in alphabetical order.
+ sis, most significant byte first. The rest of the entry is the corre-
+ sponding name, zero terminated. The names are in alphabetical order.
When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
- theses numbers. For example, consider the following pattern (assume
- PCRE_EXTENDED is set, so white space - including newlines - is
+ theses numbers. For example, consider the following pattern (assume
+ PCRE_EXTENDED is set, so white space - including newlines - is
ignored):
(?<date> (?<year>(\d\d)?\d\d) -
(?<month>\d\d) - (?<day>\d\d) )
- There are four named subpatterns, so the table has four entries, and
- each entry in the table is eight bytes long. The table is as follows,
+ There are four named subpatterns, so the table has four entries, and
+ each entry in the table is eight bytes long. The table is as follows,
with non-printing bytes shows in hexadecimal, and undefined bytes shown
as ??:
00 04 m o n t h 00
00 02 y e a r 00 ??
- When writing code to extract data from named subpatterns using the
- name-to-number map, remember that the length of the entries is likely
+ When writing code to extract data from named subpatterns using the
+ name-to-number map, remember that the length of the entries is likely
to be different for each compiled pattern.
PCRE_INFO_OKPARTIAL
- Return 1 if the pattern can be used for partial matching, otherwise 0.
- The fourth argument should point to an int variable. The pcrepartial
- documentation lists the restrictions that apply to patterns when par-
+ Return 1 if the pattern can be used for partial matching, otherwise 0.
+ The fourth argument should point to an int variable. The pcrepartial
+ documentation lists the restrictions that apply to patterns when par-
tial matching is used.
PCRE_INFO_OPTIONS
- Return a copy of the options with which the pattern was compiled. The
- fourth argument should point to an unsigned long int variable. These
+ Return a copy of the options with which the pattern was compiled. The
+ fourth argument should point to an unsigned long int variable. These
option bits are those specified in the call to pcre_compile(), modified
by any top-level option settings at the start of the pattern itself. In
- other words, they are the options that will be in force when matching
- starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
- the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
+ other words, they are the options that will be in force when matching
+ starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with
+ the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
and PCRE_EXTENDED.
- A pattern is automatically anchored by PCRE if all of its top-level
+ A pattern is automatically anchored by PCRE if all of its top-level
alternatives begin with one of the following:
^ unless PCRE_MULTILINE is set
PCRE_INFO_SIZE
- Return the size of the compiled pattern, that is, the value that was
+ Return the size of the compiled pattern, that is, the value that was
passed as the argument to pcre_malloc() when PCRE was getting memory in
which to place the compiled data. The fourth argument should point to a
size_t variable.
PCRE_INFO_STUDYSIZE
Return the size of the data block pointed to by the study_data field in
- a pcre_extra block. That is, it is the value that was passed to
+ a pcre_extra block. That is, it is the value that was passed to
pcre_malloc() when PCRE was getting memory into which to place the data
- created by pcre_study(). The fourth argument should point to a size_t
+ created by pcre_study(). The fourth argument should point to a size_t
variable.
int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
- The pcre_info() function is now obsolete because its interface is too
- restrictive to return all the available data about a compiled pattern.
- New programs should use pcre_fullinfo() instead. The yield of
- pcre_info() is the number of capturing subpatterns, or one of the fol-
+ The pcre_info() function is now obsolete because its interface is too
+ restrictive to return all the available data about a compiled pattern.
+ New programs should use pcre_fullinfo() instead. The yield of
+ pcre_info() is the number of capturing subpatterns, or one of the fol-
lowing negative numbers:
PCRE_ERROR_NULL the argument code was NULL
PCRE_ERROR_BADMAGIC the "magic number" was not found
- If the optptr argument is not NULL, a copy of the options with which
- the pattern was compiled is placed in the integer it points to (see
+ If the optptr argument is not NULL, a copy of the options with which
+ the pattern was compiled is placed in the integer it points to (see
PCRE_INFO_OPTIONS above).
- If the pattern is not anchored and the firstcharptr argument is not
- NULL, it is used to pass back information about the first character of
+ If the pattern is not anchored and the firstcharptr argument is not
+ NULL, it is used to pass back information about the first character of
any matched string (see PCRE_INFO_FIRSTBYTE above).
int pcre_refcount(pcre *code, int adjust);
- The pcre_refcount() function is used to maintain a reference count in
+ The pcre_refcount() function is used to maintain a reference count in
the data block that contains a compiled pattern. It is provided for the
- benefit of applications that operate in an object-oriented manner,
+ benefit of applications that operate in an object-oriented manner,
where different parts of the application may be using the same compiled
pattern, but you want to free the block when they are all done.
When a pattern is compiled, the reference count field is initialized to
- zero. It is changed only by calling this function, whose action is to
- add the adjust value (which may be positive or negative) to it. The
+ zero. It is changed only by calling this function, whose action is to
+ add the adjust value (which may be positive or negative) to it. The
yield of the function is the new value. However, the value of the count
- is constrained to lie between 0 and 65535, inclusive. If the new value
+ is constrained to lie between 0 and 65535, inclusive. If the new value
is outside these limits, it is forced to the appropriate limit value.
- Except when it is zero, the reference count is not correctly preserved
- if a pattern is compiled on one host and then transferred to a host
+ Except when it is zero, the reference count is not correctly preserved
+ if a pattern is compiled on one host and then transferred to a host
whose byte-order is different. (This seems a highly unlikely scenario.)
const char *subject, int length, int startoffset,
int options, int *ovector, int ovecsize);
- The function pcre_exec() is called to match a subject string against a
- compiled pattern, which is passed in the code argument. If the pattern
+ The function pcre_exec() is called to match a subject string against a
+ compiled pattern, which is passed in the code argument. If the pattern
has been studied, the result of the study should be passed in the extra
- argument. This function is the main matching facility of the library,
+ argument. This function is the main matching facility of the library,
and it operates in a Perl-like manner. For specialist use there is also
- an alternative matching function, which is described below in the sec-
+ an alternative matching function, which is described below in the sec-
tion about the pcre_dfa_exec() function.
- In most applications, the pattern will have been compiled (and option-
- ally studied) in the same process that calls pcre_exec(). However, it
+ In most applications, the pattern will have been compiled (and option-
+ ally studied) in the same process that calls pcre_exec(). However, it
is possible to save compiled patterns and study data, and then use them
- later in different processes, possibly even on different hosts. For a
+ later in different processes, possibly even on different hosts. For a
discussion about this, see the pcreprecompile documentation.
Here is an example of a simple call to pcre_exec():
Extra data for pcre_exec()
- If the extra argument is not NULL, it must point to a pcre_extra data
- block. The pcre_study() function returns such a block (when it doesn't
- return NULL), but you can also create one for yourself, and pass addi-
- tional information in it. The pcre_extra block contains the following
+ If the extra argument is not NULL, it must point to a pcre_extra data
+ block. The pcre_study() function returns such a block (when it doesn't
+ return NULL), but you can also create one for yourself, and pass addi-
+ tional information in it. The pcre_extra block contains the following
fields (not necessarily in this order):
unsigned long int flags;
void *callout_data;
const unsigned char *tables;
- The flags field is a bitmap that specifies which of the other fields
+ The flags field is a bitmap that specifies which of the other fields
are set. The flag bits are:
PCRE_EXTRA_STUDY_DATA
PCRE_EXTRA_CALLOUT_DATA
PCRE_EXTRA_TABLES
- Other flag bits should be set to zero. The study_data field is set in
- the pcre_extra block that is returned by pcre_study(), together with
+ Other flag bits should be set to zero. The study_data field is set in
+ the pcre_extra block that is returned by pcre_study(), together with
the appropriate flag bit. You should not set this yourself, but you may
- add to the block by setting the other fields and their corresponding
+ add to the block by setting the other fields and their corresponding
flag bits.
The match_limit field provides a means of preventing PCRE from using up
- a vast amount of resources when running patterns that are not going to
- match, but which have a very large number of possibilities in their
- search trees. The classic example is the use of nested unlimited
+ a vast amount of resources when running patterns that are not going to
+ match, but which have a very large number of possibilities in their
+ search trees. The classic example is the use of nested unlimited
repeats.
- Internally, PCRE uses a function called match() which it calls repeat-
- edly (sometimes recursively). The limit set by match_limit is imposed
- on the number of times this function is called during a match, which
- has the effect of limiting the amount of backtracking that can take
+ Internally, PCRE uses a function called match() which it calls repeat-
+ edly (sometimes recursively). The limit set by match_limit is imposed
+ on the number of times this function is called during a match, which
+ has the effect of limiting the amount of backtracking that can take
place. For patterns that are not anchored, the count restarts from zero
for each position in the subject string.
- The default value for the limit can be set when PCRE is built; the
- default default is 10 million, which handles all but the most extreme
- cases. You can override the default by suppling pcre_exec() with a
- pcre_extra block in which match_limit is set, and
- PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
+ The default value for the limit can be set when PCRE is built; the
+ default default is 10 million, which handles all but the most extreme
+ cases. You can override the default by suppling pcre_exec() with a
+ pcre_extra block in which match_limit is set, and
+ PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is
exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
- The match_limit_recursion field is similar to match_limit, but instead
+ The match_limit_recursion field is similar to match_limit, but instead
of limiting the total number of times that match() is called, it limits
- the depth of recursion. The recursion depth is a smaller number than
- the total number of calls, because not all calls to match() are recur-
+ the depth of recursion. The recursion depth is a smaller number than
+ the total number of calls, because not all calls to match() are recur-
sive. This limit is of use only if it is set smaller than match_limit.
- Limiting the recursion depth limits the amount of stack that can be
+ Limiting the recursion depth limits the amount of stack that can be
used, or, when PCRE has been compiled to use memory on the heap instead
of the stack, the amount of heap memory that can be used.
- The default value for match_limit_recursion can be set when PCRE is
- built; the default default is the same value as the default for
- match_limit. You can override the default by suppling pcre_exec() with
- a pcre_extra block in which match_limit_recursion is set, and
- PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
+ The default value for match_limit_recursion can be set when PCRE is
+ built; the default default is the same value as the default for
+ match_limit. You can override the default by suppling pcre_exec() with
+ a pcre_extra block in which match_limit_recursion is set, and
+ PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the
limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
- The pcre_callout field is used in conjunction with the "callout" fea-
+ The pcre_callout field is used in conjunction with the "callout" fea-
ture, which is described in the pcrecallout documentation.
- The tables field is used to pass a character tables pointer to
- pcre_exec(); this overrides the value that is stored with the compiled
- pattern. A non-NULL value is stored with the compiled pattern only if
- custom tables were supplied to pcre_compile() via its tableptr argu-
+ The tables field is used to pass a character tables pointer to
+ pcre_exec(); this overrides the value that is stored with the compiled
+ pattern. A non-NULL value is stored with the compiled pattern only if
+ custom tables were supplied to pcre_compile() via its tableptr argu-
ment. If NULL is passed to pcre_exec() using this mechanism, it forces
- PCRE's internal tables to be used. This facility is helpful when re-
- using patterns that have been saved after compiling with an external
- set of tables, because the external tables might be at a different
- address when pcre_exec() is called. See the pcreprecompile documenta-
+ PCRE's internal tables to be used. This facility is helpful when re-
+ using patterns that have been saved after compiling with an external
+ set of tables, because the external tables might be at a different
+ address when pcre_exec() is called. See the pcreprecompile documenta-
tion for a discussion of saving compiled patterns for later use.
Option bits for pcre_exec()
- The unused bits of the options argument for pcre_exec() must be zero.
- The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
+ The unused bits of the options argument for pcre_exec() must be zero.
+ The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and
PCRE_PARTIAL.
PCRE_ANCHORED
- The PCRE_ANCHORED option limits pcre_exec() to matching at the first
- matching position. If a pattern was compiled with PCRE_ANCHORED, or
- turned out to be anchored by virtue of its contents, it cannot be made
+ The PCRE_ANCHORED option limits pcre_exec() to matching at the first
+ matching position. If a pattern was compiled with PCRE_ANCHORED, or
+ turned out to be anchored by virtue of its contents, it cannot be made
unachored at matching time.
PCRE_BSR_ANYCRLF
PCRE_BSR_UNICODE
These options (which are mutually exclusive) control what the \R escape
- sequence matches. The choice is either to match only CR, LF, or CRLF,
- or to match any Unicode newline sequence. These options override the
+ sequence matches. The choice is either to match only CR, LF, or CRLF,
+ or to match any Unicode newline sequence. These options override the
choice that was made or defaulted when the pattern was compiled.
PCRE_NEWLINE_CR
PCRE_NEWLINE_ANYCRLF
PCRE_NEWLINE_ANY
- These options override the newline definition that was chosen or
- defaulted when the pattern was compiled. For details, see the descrip-
- tion of pcre_compile() above. During matching, the newline choice
- affects the behaviour of the dot, circumflex, and dollar metacharac-
- ters. It may also alter the way the match position is advanced after a
+ These options override the newline definition that was chosen or
+ defaulted when the pattern was compiled. For details, see the descrip-
+ tion of pcre_compile() above. During matching, the newline choice
+ affects the behaviour of the dot, circumflex, and dollar metacharac-
+ ters. It may also alter the way the match position is advanced after a
match failure for an unanchored pattern.
- When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
- set, and a match attempt for an unanchored pattern fails when the cur-
- rent position is at a CRLF sequence, and the pattern contains no
- explicit matches for CR or LF characters, the match position is
+ When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is
+ set, and a match attempt for an unanchored pattern fails when the cur-
+ rent position is at a CRLF sequence, and the pattern contains no
+ explicit matches for CR or LF characters, the match position is
advanced by two characters instead of one, in other words, to after the
CRLF.
The above rule is a compromise that makes the most common cases work as
- expected. For example, if the pattern is .+A (and the PCRE_DOTALL
+ expected. For example, if the pattern is .+A (and the PCRE_DOTALL
option is not set), it does not match the string "\r\nA" because, after
- failing at the start, it skips both the CR and the LF before retrying.
- However, the pattern [\r\n]A does match that string, because it con-
+ failing at the start, it skips both the CR and the LF before retrying.
+ However, the pattern [\r\n]A does match that string, because it con-
tains an explicit CR or LF reference, and so advances only by one char-
acter after the first failure.
An explicit match for CR of LF is either a literal appearance of one of
- those characters, or one of the \r or \n escape sequences. Implicit
- matches such as [^X] do not count, nor does \s (which includes CR and
+ those characters, or one of the \r or \n escape sequences. Implicit
+ matches such as [^X] do not count, nor does \s (which includes CR and
LF in the characters that it matches).
- Notwithstanding the above, anomalous effects may still occur when CRLF
+ Notwithstanding the above, anomalous effects may still occur when CRLF
is a valid newline sequence and explicit \r or \n escapes appear in the
pattern.
PCRE_NOTBOL
This option specifies that first character of the subject string is not
- the beginning of a line, so the circumflex metacharacter should not
- match before it. Setting this without PCRE_MULTILINE (at compile time)
- causes circumflex never to match. This option affects only the behav-
+ the beginning of a line, so the circumflex metacharacter should not
+ match before it. Setting this without PCRE_MULTILINE (at compile time)
+ causes circumflex never to match. This option affects only the behav-
iour of the circumflex metacharacter. It does not affect \A.
PCRE_NOTEOL
This option specifies that the end of the subject string is not the end
- of a line, so the dollar metacharacter should not match it nor (except
- in multiline mode) a newline immediately before it. Setting this with-
+ of a line, so the dollar metacharacter should not match it nor (except
+ in multiline mode) a newline immediately before it. Setting this with-
out PCRE_MULTILINE (at compile time) causes dollar never to match. This
- option affects only the behaviour of the dollar metacharacter. It does
+ option affects only the behaviour of the dollar metacharacter. It does
not affect \Z or \z.
PCRE_NOTEMPTY
An empty string is not considered to be a valid match if this option is
- set. If there are alternatives in the pattern, they are tried. If all
- the alternatives match the empty string, the entire match fails. For
+ set. If there are alternatives in the pattern, they are tried. If all
+ the alternatives match the empty string, the entire match fails. For
example, if the pattern
a?b?
- is applied to a string not beginning with "a" or "b", it matches the
- empty string at the start of the subject. With PCRE_NOTEMPTY set, this
+ is applied to a string not beginning with "a" or "b", it matches the
+ empty string at the start of the subject. With PCRE_NOTEMPTY set, this
match is not valid, so PCRE searches further into the string for occur-
rences of "a" or "b".
Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
- cial case of a pattern match of the empty string within its split()
- function, and when using the /g modifier. It is possible to emulate
+ cial case of a pattern match of the empty string within its split()
+ function, and when using the /g modifier. It is possible to emulate
Perl's behaviour after matching a null string by first trying the match
again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
- if that fails by advancing the starting offset (see below) and trying
+ if that fails by advancing the starting offset (see below) and trying
an ordinary match again. There is some code that demonstrates how to do
this in the pcredemo.c sample program.
PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set at compile time, the validity of the subject as a
- UTF-8 string is automatically checked when pcre_exec() is subsequently
- called. The value of startoffset is also checked to ensure that it
- points to the start of a UTF-8 character. There is a discussion about
- the validity of UTF-8 strings in the section on UTF-8 support in the
- main pcre page. If an invalid UTF-8 sequence of bytes is found,
- pcre_exec() returns the error PCRE_ERROR_BADUTF8. If startoffset con-
+ UTF-8 string is automatically checked when pcre_exec() is subsequently
+ called. The value of startoffset is also checked to ensure that it
+ points to the start of a UTF-8 character. There is a discussion about
+ the validity of UTF-8 strings in the section on UTF-8 support in the
+ main pcre page. If an invalid UTF-8 sequence of bytes is found,
+ pcre_exec() returns the error PCRE_ERROR_BADUTF8. If startoffset con-
tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
- If you already know that your subject is valid, and you want to skip
- these checks for performance reasons, you can set the
- PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
- do this for the second and subsequent calls to pcre_exec() if you are
- making repeated calls to find all the matches in a single subject
- string. However, you should be sure that the value of startoffset
- points to the start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
- set, the effect of passing an invalid UTF-8 string as a subject, or a
- value of startoffset that does not point to the start of a UTF-8 char-
+ If you already know that your subject is valid, and you want to skip
+ these checks for performance reasons, you can set the
+ PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to
+ do this for the second and subsequent calls to pcre_exec() if you are
+ making repeated calls to find all the matches in a single subject
+ string. However, you should be sure that the value of startoffset
+ points to the start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
+ set, the effect of passing an invalid UTF-8 string as a subject, or a
+ value of startoffset that does not point to the start of a UTF-8 char-
acter, is undefined. Your program may crash.
PCRE_PARTIAL
- This option turns on the partial matching feature. If the subject
- string fails to match the pattern, but at some point during the match-
- ing process the end of the subject was reached (that is, the subject
- partially matches the pattern and the failure to match occurred only
- because there were not enough subject characters), pcre_exec() returns
- PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
- used, there are restrictions on what may appear in the pattern. These
+ This option turns on the partial matching feature. If the subject
+ string fails to match the pattern, but at some point during the match-
+ ing process the end of the subject was reached (that is, the subject
+ partially matches the pattern and the failure to match occurred only
+ because there were not enough subject characters), pcre_exec() returns
+ PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
+ used, there are restrictions on what may appear in the pattern. These
are discussed in the pcrepartial documentation.
The string to be matched by pcre_exec()
- The subject string is passed to pcre_exec() as a pointer in subject, a
- length in length, and a starting byte offset in startoffset. In UTF-8
- mode, the byte offset must point to the start of a UTF-8 character.
- Unlike the pattern string, the subject may contain binary zero bytes.
- When the starting offset is zero, the search for a match starts at the
+ The subject string is passed to pcre_exec() as a pointer in subject, a
+ length in length, and a starting byte offset in startoffset. In UTF-8
+ mode, the byte offset must point to the start of a UTF-8 character.
+ Unlike the pattern string, the subject may contain binary zero bytes.
+ When the starting offset is zero, the search for a match starts at the
beginning of the subject, and this is by far the most common case.
- A non-zero starting offset is useful when searching for another match
- in the same subject by calling pcre_exec() again after a previous suc-
- cess. Setting startoffset differs from just passing over a shortened
- string and setting PCRE_NOTBOL in the case of a pattern that begins
+ A non-zero starting offset is useful when searching for another match
+ in the same subject by calling pcre_exec() again after a previous suc-
+ cess. Setting startoffset differs from just passing over a shortened
+ string and setting PCRE_NOTBOL in the case of a pattern that begins
with any kind of lookbehind. For example, consider the pattern
\Biss\B
- which finds occurrences of "iss" in the middle of words. (\B matches
- only if the current position in the subject is not a word boundary.)
- When applied to the string "Mississipi" the first call to pcre_exec()
- finds the first occurrence. If pcre_exec() is called again with just
- the remainder of the subject, namely "issipi", it does not match,
+ which finds occurrences of "iss" in the middle of words. (\B matches
+ only if the current position in the subject is not a word boundary.)
+ When applied to the string "Mississipi" the first call to pcre_exec()
+ finds the first occurrence. If pcre_exec() is called again with just
+ the remainder of the subject, namely "issipi", it does not match,
because \B is always false at the start of the subject, which is deemed
- to be a word boundary. However, if pcre_exec() is passed the entire
+ to be a word boundary. However, if pcre_exec() is passed the entire
string again, but with startoffset set to 4, it finds the second occur-
- rence of "iss" because it is able to look behind the starting point to
+ rence of "iss" because it is able to look behind the starting point to
discover that it is preceded by a letter.
- If a non-zero starting offset is passed when the pattern is anchored,
+ If a non-zero starting offset is passed when the pattern is anchored,
one attempt to match at the given offset is made. This can only succeed
- if the pattern does not require the match to be at the start of the
+ if the pattern does not require the match to be at the start of the
subject.
How pcre_exec() returns captured substrings
- In general, a pattern matches a certain portion of the subject, and in
- addition, further substrings from the subject may be picked out by
- parts of the pattern. Following the usage in Jeffrey Friedl's book,
- this is called "capturing" in what follows, and the phrase "capturing
- subpattern" is used for a fragment of a pattern that picks out a sub-
- string. PCRE supports several other kinds of parenthesized subpattern
+ In general, a pattern matches a certain portion of the subject, and in
+ addition, further substrings from the subject may be picked out by
+ parts of the pattern. Following the usage in Jeffrey Friedl's book,
+ this is called "capturing" in what follows, and the phrase "capturing
+ subpattern" is used for a fragment of a pattern that picks out a sub-
+ string. PCRE supports several other kinds of parenthesized subpattern
that do not cause substrings to be captured.
- Captured substrings are returned to the caller via a vector of integer
- offsets whose address is passed in ovector. The number of elements in
- the vector is passed in ovecsize, which must be a non-negative number.
+ Captured substrings are returned to the caller via a vector of integer
+ offsets whose address is passed in ovector. The number of elements in
+ the vector is passed in ovecsize, which must be a non-negative number.
Note: this argument is NOT the size of ovector in bytes.
- The first two-thirds of the vector is used to pass back captured sub-
- strings, each substring using a pair of integers. The remaining third
- of the vector is used as workspace by pcre_exec() while matching cap-
- turing subpatterns, and is not available for passing back information.
- The length passed in ovecsize should always be a multiple of three. If
+ The first two-thirds of the vector is used to pass back captured sub-
+ strings, each substring using a pair of integers. The remaining third
+ of the vector is used as workspace by pcre_exec() while matching cap-
+ turing subpatterns, and is not available for passing back information.
+ The length passed in ovecsize should always be a multiple of three. If
it is not, it is rounded down.
- When a match is successful, information about captured substrings is
- returned in pairs of integers, starting at the beginning of ovector,
- and continuing up to two-thirds of its length at the most. The first
+ When a match is successful, information about captured substrings is
+ returned in pairs of integers, starting at the beginning of ovector,
+ and continuing up to two-thirds of its length at the most. The first
element of a pair is set to the offset of the first character in a sub-
- string, and the second is set to the offset of the first character
- after the end of a substring. The first pair, ovector[0] and ovec-
- tor[1], identify the portion of the subject string matched by the
- entire pattern. The next pair is used for the first capturing subpat-
+ string, and the second is set to the offset of the first character
+ after the end of a substring. The first pair, ovector[0] and ovec-
+ tor[1], identify the portion of the subject string matched by the
+ entire pattern. The next pair is used for the first capturing subpat-
tern, and so on. The value returned by pcre_exec() is one more than the
highest numbered pair that has been set. For example, if two substrings
- have been captured, the returned value is 3. If there are no capturing
- subpatterns, the return value from a successful match is 1, indicating
+ have been captured, the returned value is 3. If there are no capturing
+ subpatterns, the return value from a successful match is 1, indicating
that just the first pair of offsets has been set.
If a capturing subpattern is matched repeatedly, it is the last portion
of the string that it matched that is returned.
- If the vector is too small to hold all the captured substring offsets,
+ If the vector is too small to hold all the captured substring offsets,
it is used as far as possible (up to two-thirds of its length), and the
- function returns a value of zero. In particular, if the substring off-
+ function returns a value of zero. In particular, if the substring off-
sets are not of interest, pcre_exec() may be called with ovector passed
- as NULL and ovecsize as zero. However, if the pattern contains back
- references and the ovector is not big enough to remember the related
- substrings, PCRE has to get additional memory for use during matching.
+ as NULL and ovecsize as zero. However, if the pattern contains back
+ references and the ovector is not big enough to remember the related
+ substrings, PCRE has to get additional memory for use during matching.
Thus it is usually advisable to supply an ovector.
- The pcre_info() function can be used to find out how many capturing
- subpatterns there are in a compiled pattern. The smallest size for
- ovector that will allow for n captured substrings, in addition to the
+ The pcre_info() function can be used to find out how many capturing
+ subpatterns there are in a compiled pattern. The smallest size for
+ ovector that will allow for n captured substrings, in addition to the
offsets of the substring matched by the whole pattern, is (n+1)*3.
- It is possible for capturing subpattern number n+1 to match some part
+ It is possible for capturing subpattern number n+1 to match some part
of the subject when subpattern n has not been used at all. For example,
- if the string "abc" is matched against the pattern (a|(z))(bc) the
+ if the string "abc" is matched against the pattern (a|(z))(bc) the
return from the function is 4, and subpatterns 1 and 3 are matched, but
- 2 is not. When this happens, both values in the offset pairs corre-
+ 2 is not. When this happens, both values in the offset pairs corre-
sponding to unused subpatterns are set to -1.
- Offset values that correspond to unused subpatterns at the end of the
- expression are also set to -1. For example, if the string "abc" is
- matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
- matched. The return from the function is 2, because the highest used
+ Offset values that correspond to unused subpatterns at the end of the
+ expression are also set to -1. For example, if the string "abc" is
+ matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
+ matched. The return from the function is 2, because the highest used
capturing subpattern number is 1. However, you can refer to the offsets
- for the second and third capturing subpatterns if you wish (assuming
+ for the second and third capturing subpatterns if you wish (assuming
the vector is large enough, of course).
- Some convenience functions are provided for extracting the captured
+ Some convenience functions are provided for extracting the captured
substrings as separate strings. These are described below.
Error return values from pcre_exec()
- If pcre_exec() fails, it returns a negative number. The following are
+ If pcre_exec() fails, it returns a negative number. The following are
defined in the header file:
PCRE_ERROR_NOMATCH (-1)
PCRE_ERROR_NULL (-2)
- Either code or subject was passed as NULL, or ovector was NULL and
+ Either code or subject was passed as NULL, or ovector was NULL and
ovecsize was not zero.
PCRE_ERROR_BADOPTION (-3)
PCRE_ERROR_BADMAGIC (-4)
- PCRE stores a 4-byte "magic number" at the start of the compiled code,
+ PCRE stores a 4-byte "magic number" at the start of the compiled code,
to catch the case when it is passed a junk pointer and to detect when a
pattern that was compiled in an environment of one endianness is run in
- an environment with the other endianness. This is the error that PCRE
+ an environment with the other endianness. This is the error that PCRE
gives when the magic number is not present.
PCRE_ERROR_UNKNOWN_OPCODE (-5)
While running the pattern match, an unknown item was encountered in the
- compiled pattern. This error could be caused by a bug in PCRE or by
+ compiled pattern. This error could be caused by a bug in PCRE or by
overwriting of the compiled pattern.
PCRE_ERROR_NOMEMORY (-6)
- If a pattern contains back references, but the ovector that is passed
+ If a pattern contains back references, but the ovector that is passed
to pcre_exec() is not big enough to remember the referenced substrings,
- PCRE gets a block of memory at the start of matching to use for this
- purpose. If the call via pcre_malloc() fails, this error is given. The
+ PCRE gets a block of memory at the start of matching to use for this
+ purpose. If the call via pcre_malloc() fails, this error is given. The
memory is automatically freed at the end of matching.
PCRE_ERROR_NOSUBSTRING (-7)
- This error is used by the pcre_copy_substring(), pcre_get_substring(),
+ This error is used by the pcre_copy_substring(), pcre_get_substring(),
and pcre_get_substring_list() functions (see below). It is never
returned by pcre_exec().
PCRE_ERROR_MATCHLIMIT (-8)
- The backtracking limit, as specified by the match_limit field in a
- pcre_extra structure (or defaulted) was reached. See the description
+ The backtracking limit, as specified by the match_limit field in a
+ pcre_extra structure (or defaulted) was reached. See the description
above.
PCRE_ERROR_CALLOUT (-9)
This error is never generated by pcre_exec() itself. It is provided for
- use by callout functions that want to yield a distinctive error code.
+ use by callout functions that want to yield a distinctive error code.
See the pcrecallout documentation for details.
PCRE_ERROR_BADUTF8 (-10)
- A string that contains an invalid UTF-8 byte sequence was passed as a
+ A string that contains an invalid UTF-8 byte sequence was passed as a
subject.
PCRE_ERROR_BADUTF8_OFFSET (-11)
The UTF-8 byte sequence that was passed as a subject was valid, but the
- value of startoffset did not point to the beginning of a UTF-8 charac-
+ value of startoffset did not point to the beginning of a UTF-8 charac-
ter.
PCRE_ERROR_PARTIAL (-12)
- The subject string did not match, but it did match partially. See the
+ The subject string did not match, but it did match partially. See the
pcrepartial documentation for details of partial matching.
PCRE_ERROR_BADPARTIAL (-13)
- The PCRE_PARTIAL option was used with a compiled pattern containing
- items that are not supported for partial matching. See the pcrepartial
+ The PCRE_PARTIAL option was used with a compiled pattern containing
+ items that are not supported for partial matching. See the pcrepartial
documentation for details of partial matching.
PCRE_ERROR_INTERNAL (-14)
- An unexpected internal error has occurred. This error could be caused
+ An unexpected internal error has occurred. This error could be caused
by a bug in PCRE or by overwriting of the compiled pattern.
PCRE_ERROR_BADCOUNT (-15)
- This error is given if the value of the ovecsize argument is negative.
+ This error is given if the value of the ovecsize argument is negative.
PCRE_ERROR_RECURSIONLIMIT (-21)
The internal recursion limit, as specified by the match_limit_recursion
- field in a pcre_extra structure (or defaulted) was reached. See the
+ field in a pcre_extra structure (or defaulted) was reached. See the
description above.
PCRE_ERROR_BADNEWLINE (-23)
int pcre_get_substring_list(const char *subject,
int *ovector, int stringcount, const char ***listptr);
- Captured substrings can be accessed directly by using the offsets
- returned by pcre_exec() in ovector. For convenience, the functions
+ Captured substrings can be accessed directly by using the offsets
+ returned by pcre_exec() in ovector. For convenience, the functions
pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub-
- string_list() are provided for extracting captured substrings as new,
- separate, zero-terminated strings. These functions identify substrings
- by number. The next section describes functions for extracting named
+ string_list() are provided for extracting captured substrings as new,
+ separate, zero-terminated strings. These functions identify substrings
+ by number. The next section describes functions for extracting named
substrings.
- A substring that contains a binary zero is correctly extracted and has
- a further zero added on the end, but the result is not, of course, a C
- string. However, you can process such a string by referring to the
- length that is returned by pcre_copy_substring() and pcre_get_sub-
+ A substring that contains a binary zero is correctly extracted and has
+ a further zero added on the end, but the result is not, of course, a C
+ string. However, you can process such a string by referring to the
+ length that is returned by pcre_copy_substring() and pcre_get_sub-
string(). Unfortunately, the interface to pcre_get_substring_list() is
- not adequate for handling strings containing binary zeros, because the
+ not adequate for handling strings containing binary zeros, because the
end of the final string is not independently indicated.
- The first three arguments are the same for all three of these func-
- tions: subject is the subject string that has just been successfully
+ The first three arguments are the same for all three of these func-
+ tions: subject is the subject string that has just been successfully
matched, ovector is a pointer to the vector of integer offsets that was
passed to pcre_exec(), and stringcount is the number of substrings that
- were captured by the match, including the substring that matched the
+ were captured by the match, including the substring that matched the
entire regular expression. This is the value returned by pcre_exec() if
- it is greater than zero. If pcre_exec() returned zero, indicating that
- it ran out of space in ovector, the value passed as stringcount should
+ it is greater than zero. If pcre_exec() returned zero, indicating that
+ it ran out of space in ovector, the value passed as stringcount should
be the number of elements in the vector divided by three.
- The functions pcre_copy_substring() and pcre_get_substring() extract a
- single substring, whose number is given as stringnumber. A value of
- zero extracts the substring that matched the entire pattern, whereas
- higher values extract the captured substrings. For pcre_copy_sub-
- string(), the string is placed in buffer, whose length is given by
- buffersize, while for pcre_get_substring() a new block of memory is
- obtained via pcre_malloc, and its address is returned via stringptr.
- The yield of the function is the length of the string, not including
+ The functions pcre_copy_substring() and pcre_get_substring() extract a
+ single substring, whose number is given as stringnumber. A value of
+ zero extracts the substring that matched the entire pattern, whereas
+ higher values extract the captured substrings. For pcre_copy_sub-
+ string(), the string is placed in buffer, whose length is given by
+ buffersize, while for pcre_get_substring() a new block of memory is
+ obtained via pcre_malloc, and its address is returned via stringptr.
+ The yield of the function is the length of the string, not including
the terminating zero, or one of these error codes:
PCRE_ERROR_NOMEMORY (-6)
- The buffer was too small for pcre_copy_substring(), or the attempt to
+ The buffer was too small for pcre_copy_substring(), or the attempt to
get memory failed for pcre_get_substring().
PCRE_ERROR_NOSUBSTRING (-7)
There is no substring whose number is stringnumber.
- The pcre_get_substring_list() function extracts all available sub-
- strings and builds a list of pointers to them. All this is done in a
+ The pcre_get_substring_list() function extracts all available sub-
+ strings and builds a list of pointers to them. All this is done in a
single block of memory that is obtained via pcre_malloc. The address of
- the memory block is returned via listptr, which is also the start of
- the list of string pointers. The end of the list is marked by a NULL
- pointer. The yield of the function is zero if all went well, or the
+ the memory block is returned via listptr, which is also the start of
+ the list of string pointers. The end of the list is marked by a NULL
+ pointer. The yield of the function is zero if all went well, or the
error code
PCRE_ERROR_NOMEMORY (-6)
if the attempt to get the memory block failed.
- When any of these functions encounter a substring that is unset, which
- can happen when capturing subpattern number n+1 matches some part of
- the subject, but subpattern n has not been used at all, they return an
+ When any of these functions encounter a substring that is unset, which
+ can happen when capturing subpattern number n+1 matches some part of
+ the subject, but subpattern n has not been used at all, they return an
empty string. This can be distinguished from a genuine zero-length sub-
- string by inspecting the appropriate offset in ovector, which is nega-
+ string by inspecting the appropriate offset in ovector, which is nega-
tive for unset substrings.
- The two convenience functions pcre_free_substring() and pcre_free_sub-
- string_list() can be used to free the memory returned by a previous
+ The two convenience functions pcre_free_substring() and pcre_free_sub-
+ string_list() can be used to free the memory returned by a previous
call of pcre_get_substring() or pcre_get_substring_list(), respec-
- tively. They do nothing more than call the function pointed to by
- pcre_free, which of course could be called directly from a C program.
- However, PCRE is used in some situations where it is linked via a spe-
- cial interface to another programming language that cannot use
- pcre_free directly; it is for these cases that the functions are pro-
+ tively. They do nothing more than call the function pointed to by
+ pcre_free, which of course could be called directly from a C program.
+ However, PCRE is used in some situations where it is linked via a spe-
+ cial interface to another programming language that cannot use
+ pcre_free directly; it is for these cases that the functions are pro-
vided.
int stringcount, const char *stringname,
const char **stringptr);
- To extract a substring by name, you first have to find associated num-
+ To extract a substring by name, you first have to find associated num-
ber. For example, for this pattern
(a+)b(?<xxx>\d+)...
be unique (PCRE_DUPNAMES was not set), you can find the number from the
name by calling pcre_get_stringnumber(). The first argument is the com-
piled pattern, and the second is the name. The yield of the function is
- the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
+ the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no
subpattern of that name.
Given the number, you can extract the substring directly, or use one of
the functions described in the previous section. For convenience, there
are also two functions that do the whole job.
- Most of the arguments of pcre_copy_named_substring() and
- pcre_get_named_substring() are the same as those for the similarly
- named functions that extract by number. As these are described in the
- previous section, they are not re-described here. There are just two
+ Most of the arguments of pcre_copy_named_substring() and
+ pcre_get_named_substring() are the same as those for the similarly
+ named functions that extract by number. As these are described in the
+ previous section, they are not re-described here. There are just two
differences:
- First, instead of a substring number, a substring name is given. Sec-
+ First, instead of a substring number, a substring name is given. Sec-
ond, there is an extra argument, given at the start, which is a pointer
- to the compiled pattern. This is needed in order to gain access to the
+ to the compiled pattern. This is needed in order to gain access to the
name-to-number translation table.
- These functions call pcre_get_stringnumber(), and if it succeeds, they
- then call pcre_copy_substring() or pcre_get_substring(), as appropri-
- ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
+ These functions call pcre_get_stringnumber(), and if it succeeds, they
+ then call pcre_copy_substring() or pcre_get_substring(), as appropri-
+ ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the
behaviour may not be what you want (see the next section).
int pcre_get_stringtable_entries(const pcre *code,
const char *name, char **first, char **last);
- When a pattern is compiled with the PCRE_DUPNAMES option, names for
- subpatterns are not required to be unique. Normally, patterns with
- duplicate names are such that in any one match, only one of the named
- subpatterns participates. An example is shown in the pcrepattern docu-
+ When a pattern is compiled with the PCRE_DUPNAMES option, names for
+ subpatterns are not required to be unique. Normally, patterns with
+ duplicate names are such that in any one match, only one of the named
+ subpatterns participates. An example is shown in the pcrepattern docu-
mentation.
- When duplicates are present, pcre_copy_named_substring() and
- pcre_get_named_substring() return the first substring corresponding to
- the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
- (-7) is returned; no data is returned. The pcre_get_stringnumber()
- function returns one of the numbers that are associated with the name,
+ When duplicates are present, pcre_copy_named_substring() and
+ pcre_get_named_substring() return the first substring corresponding to
+ the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING
+ (-7) is returned; no data is returned. The pcre_get_stringnumber()
+ function returns one of the numbers that are associated with the name,
but it is not defined which it is.
- If you want to get full details of all captured substrings for a given
- name, you must use the pcre_get_stringtable_entries() function. The
+ If you want to get full details of all captured substrings for a given
+ name, you must use the pcre_get_stringtable_entries() function. The
first argument is the compiled pattern, and the second is the name. The
- third and fourth are pointers to variables which are updated by the
+ third and fourth are pointers to variables which are updated by the
function. After it has run, they point to the first and last entries in
- the name-to-number table for the given name. The function itself
- returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
- there are none. The format of the table is described above in the sec-
- tion entitled Information about a pattern. Given all the relevant
- entries for the name, you can extract each of their numbers, and hence
+ the name-to-number table for the given name. The function itself
+ returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
+ there are none. The format of the table is described above in the sec-
+ tion entitled Information about a pattern. Given all the relevant
+ entries for the name, you can extract each of their numbers, and hence
the captured data, if any.
FINDING ALL POSSIBLE MATCHES
- The traditional matching function uses a similar algorithm to Perl,
+ The traditional matching function uses a similar algorithm to Perl,
which stops when it finds the first match, starting at a given point in
- the subject. If you want to find all possible matches, or the longest
- possible match, consider using the alternative matching function (see
- below) instead. If you cannot use the alternative function, but still
- need to find all possible matches, you can kludge it up by making use
+ the subject. If you want to find all possible matches, or the longest
+ possible match, consider using the alternative matching function (see
+ below) instead. If you cannot use the alternative function, but still
+ need to find all possible matches, you can kludge it up by making use
of the callout facility, which is described in the pcrecallout documen-
tation.
What you have to do is to insert a callout right at the end of the pat-
- tern. When your callout function is called, extract and save the cur-
- rent matched substring. Then return 1, which forces pcre_exec() to
- backtrack and try other alternatives. Ultimately, when it runs out of
+ tern. When your callout function is called, extract and save the cur-
+ rent matched substring. Then return 1, which forces pcre_exec() to
+ backtrack and try other alternatives. Ultimately, when it runs out of
matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
int options, int *ovector, int ovecsize,
int *workspace, int wscount);
- The function pcre_dfa_exec() is called to match a subject string
- against a compiled pattern, using a matching algorithm that scans the
- subject string just once, and does not backtrack. This has different
- characteristics to the normal algorithm, and is not compatible with
- Perl. Some of the features of PCRE patterns are not supported. Never-
- theless, there are times when this kind of matching can be useful. For
+ The function pcre_dfa_exec() is called to match a subject string
+ against a compiled pattern, using a matching algorithm that scans the
+ subject string just once, and does not backtrack. This has different
+ characteristics to the normal algorithm, and is not compatible with
+ Perl. Some of the features of PCRE patterns are not supported. Never-
+ theless, there are times when this kind of matching can be useful. For
a discussion of the two matching algorithms, see the pcrematching docu-
mentation.
- The arguments for the pcre_dfa_exec() function are the same as for
+ The arguments for the pcre_dfa_exec() function are the same as for
pcre_exec(), plus two extras. The ovector argument is used in a differ-
- ent way, and this is described below. The other common arguments are
- used in the same way as for pcre_exec(), so their description is not
+ ent way, and this is described below. The other common arguments are
+ used in the same way as for pcre_exec(), so their description is not
repeated here.
- The two additional arguments provide workspace for the function. The
- workspace vector should contain at least 20 elements. It is used for
+ The two additional arguments provide workspace for the function. The
+ workspace vector should contain at least 20 elements. It is used for
keeping track of multiple paths through the pattern tree. More
- workspace will be needed for patterns and subjects where there are a
+ workspace will be needed for patterns and subjects where there are a
lot of potential matches.
Here is an example of a simple call to pcre_dfa_exec():
Option bits for pcre_dfa_exec()
- The unused bits of the options argument for pcre_dfa_exec() must be
- zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
- LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
+ The unused bits of the options argument for pcre_dfa_exec() must be
+ zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW-
+ LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
three of these are the same as for pcre_exec(), so their description is
not repeated here.
PCRE_PARTIAL
- This has the same general effect as it does for pcre_exec(), but the
- details are slightly different. When PCRE_PARTIAL is set for
- pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is converted into
- PCRE_ERROR_PARTIAL if the end of the subject is reached, there have
+ This has the same general effect as it does for pcre_exec(), but the
+ details are slightly different. When PCRE_PARTIAL is set for
+ pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is converted into
+ PCRE_ERROR_PARTIAL if the end of the subject is reached, there have
been no complete matches, but there is still at least one matching pos-
- sibility. The portion of the string that provided the partial match is
+ sibility. The portion of the string that provided the partial match is
set as the first matching string.
PCRE_DFA_SHORTEST
- Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
+ Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to
stop as soon as it has found one match. Because of the way the alterna-
- tive algorithm works, this is necessarily the shortest possible match
+ tive algorithm works, this is necessarily the shortest possible match
at the first possible matching point in the subject string.
PCRE_DFA_RESTART
- When pcre_dfa_exec() is called with the PCRE_PARTIAL option, and
- returns a partial match, it is possible to call it again, with addi-
- tional subject characters, and have it continue with the same match.
- The PCRE_DFA_RESTART option requests this action; when it is set, the
- workspace and wscount options must reference the same vector as before
- because data about the match so far is left in them after a partial
- match. There is more discussion of this facility in the pcrepartial
+ When pcre_dfa_exec() is called with the PCRE_PARTIAL option, and
+ returns a partial match, it is possible to call it again, with addi-
+ tional subject characters, and have it continue with the same match.
+ The PCRE_DFA_RESTART option requests this action; when it is set, the
+ workspace and wscount options must reference the same vector as before
+ because data about the match so far is left in them after a partial
+ match. There is more discussion of this facility in the pcrepartial
documentation.
Successful returns from pcre_dfa_exec()
- When pcre_dfa_exec() succeeds, it may have matched more than one sub-
+ When pcre_dfa_exec() succeeds, it may have matched more than one sub-
string in the subject. Note, however, that all the matches from one run
- of the function start at the same point in the subject. The shorter
- matches are all initial substrings of the longer matches. For example,
+ of the function start at the same point in the subject. The shorter
+ matches are all initial substrings of the longer matches. For example,
if the pattern
<.*>
<something> <something else>
<something> <something else> <something further>
- On success, the yield of the function is a number greater than zero,
- which is the number of matched substrings. The substrings themselves
- are returned in ovector. Each string uses two elements; the first is
- the offset to the start, and the second is the offset to the end. In
- fact, all the strings have the same start offset. (Space could have
- been saved by giving this only once, but it was decided to retain some
- compatibility with the way pcre_exec() returns data, even though the
+ On success, the yield of the function is a number greater than zero,
+ which is the number of matched substrings. The substrings themselves
+ are returned in ovector. Each string uses two elements; the first is
+ the offset to the start, and the second is the offset to the end. In
+ fact, all the strings have the same start offset. (Space could have
+ been saved by giving this only once, but it was decided to retain some
+ compatibility with the way pcre_exec() returns data, even though the
meaning of the strings is different.)
The strings are returned in reverse order of length; that is, the long-
- est matching string is given first. If there were too many matches to
- fit into ovector, the yield of the function is zero, and the vector is
+ est matching string is given first. If there were too many matches to
+ fit into ovector, the yield of the function is zero, and the vector is
filled with the longest matches.
Error returns from pcre_dfa_exec()
- The pcre_dfa_exec() function returns a negative number when it fails.
- Many of the errors are the same as for pcre_exec(), and these are
- described above. There are in addition the following errors that are
+ The pcre_dfa_exec() function returns a negative number when it fails.
+ Many of the errors are the same as for pcre_exec(), and these are
+ described above. There are in addition the following errors that are
specific to pcre_dfa_exec():
PCRE_ERROR_DFA_UITEM (-16)
- This return is given if pcre_dfa_exec() encounters an item in the pat-
- tern that it does not support, for instance, the use of \C or a back
+ This return is given if pcre_dfa_exec() encounters an item in the pat-
+ tern that it does not support, for instance, the use of \C or a back
reference.
PCRE_ERROR_DFA_UCOND (-17)
- This return is given if pcre_dfa_exec() encounters a condition item
- that uses a back reference for the condition, or a test for recursion
+ This return is given if pcre_dfa_exec() encounters a condition item
+ that uses a back reference for the condition, or a test for recursion
in a specific group. These are not supported.
PCRE_ERROR_DFA_UMLIMIT (-18)
- This return is given if pcre_dfa_exec() is called with an extra block
+ This return is given if pcre_dfa_exec() is called with an extra block
that contains a setting of the match_limit field. This is not supported
(it is meaningless).
PCRE_ERROR_DFA_WSSIZE (-19)
- This return is given if pcre_dfa_exec() runs out of space in the
+ This return is given if pcre_dfa_exec() runs out of space in the
workspace vector.
PCRE_ERROR_DFA_RECURSE (-20)
- When a recursive subpattern is processed, the matching function calls
- itself recursively, using private vectors for ovector and workspace.
- This error is given if the output vector is not large enough. This
+ When a recursive subpattern is processed, the matching function calls
+ itself recursively, using private vectors for ovector and workspace.
+ This error is given if the output vector is not large enough. This
should be extremely rare, as a vector of size 1000 is used.
SEE ALSO
- pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
- tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
+ pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
+ tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
AUTHOR
REVISION
- Last updated: 23 January 2008
+ Last updated: 12 April 2008
Copyright (c) 1997-2008 University of Cambridge.
------------------------------------------------------------------------------
The syntax and semantics of the regular expressions that are supported
by PCRE are described in detail below. There is a quick-reference syn-
- tax summary in the pcresyntax page. Perl's regular expressions are
- described in its own documentation, and regular expressions in general
- are covered in a number of books, some of which have copious examples.
- Jeffrey Friedl's "Mastering Regular Expressions", published by
- O'Reilly, covers regular expressions in great detail. This description
- of PCRE's regular expressions is intended as reference material.
+ tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
+ semantics as closely as it can. PCRE also supports some alternative
+ regular expression syntax (which does not conflict with the Perl syn-
+ tax) in order to provide some compatibility with regular expressions in
+ Python, .NET, and Oniguruma.
+
+ Perl's regular expressions are described in its own documentation, and
+ regular expressions in general are covered in a number of books, some
+ of which have copious examples. Jeffrey Friedl's "Mastering Regular
+ Expressions", published by O'Reilly, covers regular expressions in
+ great detail. This description of PCRE's regular expressions is
+ intended as reference material.
The original operation of PCRE was on strings of one-byte characters.
However, there is now also support for UTF-8 character strings. To use
named back reference can be coded as \g{name}. Back references are dis-
cussed later, following the discussion of parenthesized subpatterns.
+ Absolute and relative subroutine calls
+
+ For compatibility with Oniguruma, the non-Perl syntax \g followed by a
+ name or a number enclosed either in angle brackets or single quotes, is
+ an alternative syntax for referencing a subpattern as a "subroutine".
+ Details are discussed later. Note that \g{...} (Perl syntax) and
+ \g<...> (Oniguruma syntax) are not synonymous. The former is a back
+ reference; the latter is a subroutine call.
+
Generic character types
Another use of backslash is for specifying generic character types. The
\W any "non-word" character
Each pair of escape sequences partitions the complete set of characters
- into two disjoint sets. Any given character matches one, and only one,
+ into two disjoint sets. Any given character matches one, and only one,
of each pair.
These character type sequences can appear both inside and outside char-
- acter classes. They each match one character of the appropriate type.
- If the current matching point is at the end of the subject string, all
+ acter classes. They each match one character of the appropriate type.
+ If the current matching point is at the end of the subject string, all
of them fail, since there is no character to match.
- For compatibility with Perl, \s does not match the VT character (code
- 11). This makes it different from the the POSIX "space" class. The \s
- characters are HT (9), LF (10), FF (12), CR (13), and space (32). If
+ For compatibility with Perl, \s does not match the VT character (code
+ 11). This makes it different from the the POSIX "space" class. The \s
+ characters are HT (9), LF (10), FF (12), CR (13), and space (32). If
"use locale;" is included in a Perl script, \s may match the VT charac-
ter. In PCRE, it never does.
- In UTF-8 mode, characters with values greater than 128 never match \d,
+ In UTF-8 mode, characters with values greater than 128 never match \d,
\s, or \w, and always match \D, \S, and \W. This is true even when Uni-
- code character property support is available. These sequences retain
+ code character property support is available. These sequences retain
their original meanings from before UTF-8 support was available, mainly
for efficiency reasons.
The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
- the other sequences, these do match certain high-valued codepoints in
+ the other sequences, these do match certain high-valued codepoints in
UTF-8 mode. The horizontal space characters are:
U+0009 Horizontal tab
U+2029 Paragraph separator
A "word" character is an underscore or any character less than 256 that
- is a letter or digit. The definition of letters and digits is con-
- trolled by PCRE's low-valued character tables, and may vary if locale-
- specific matching is taking place (see "Locale support" in the pcreapi
- page). For example, in a French locale such as "fr_FR" in Unix-like
- systems, or "french" in Windows, some character codes greater than 128
- are used for accented letters, and these are matched by \w. The use of
+ is a letter or digit. The definition of letters and digits is con-
+ trolled by PCRE's low-valued character tables, and may vary if locale-
+ specific matching is taking place (see "Locale support" in the pcreapi
+ page). For example, in a French locale such as "fr_FR" in Unix-like
+ systems, or "french" in Windows, some character codes greater than 128
+ are used for accented letters, and these are matched by \w. The use of
locales with Unicode is discouraged.
Newline sequences
- Outside a character class, by default, the escape sequence \R matches
+ Outside a character class, by default, the escape sequence \R matches
any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
mode \R is equivalent to the following:
(?>\r\n|\n|\x0b|\f|\r|\x85)
- This is an example of an "atomic group", details of which are given
+ This is an example of an "atomic group", details of which are given
below. This particular group matches either the two-character sequence
- CR followed by LF, or one of the single characters LF (linefeed,
+ CR followed by LF, or one of the single characters LF (linefeed,
U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
return, U+000D), or NEL (next line, U+0085). The two-character sequence
is treated as a single unit that cannot be split.
- In UTF-8 mode, two additional characters whose codepoints are greater
+ In UTF-8 mode, two additional characters whose codepoints are greater
than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
- rator, U+2029). Unicode character property support is not needed for
+ rator, U+2029). Unicode character property support is not needed for
these characters to be recognized.
It is possible to restrict \R to match only CR, LF, or CRLF (instead of
- the complete set of Unicode line endings) by setting the option
+ the complete set of Unicode line endings) by setting the option
PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
(BSR is an abbrevation for "backslash R".) This can be made the default
- when PCRE is built; if this is the case, the other behaviour can be
- requested via the PCRE_BSR_UNICODE option. It is also possible to
- specify these settings by starting a pattern string with one of the
+ when PCRE is built; if this is the case, the other behaviour can be
+ requested via the PCRE_BSR_UNICODE option. It is also possible to
+ specify these settings by starting a pattern string with one of the
following sequences:
(*BSR_ANYCRLF) CR, LF, or CRLF only
These override the default and the options given to pcre_compile(), but
they can be overridden by options given to pcre_exec(). Note that these
special settings, which are not Perl-compatible, are recognized only at
- the very start of a pattern, and that they must be in upper case. If
- more than one of them is present, the last one is used. They can be
- combined with a change of newline convention, for example, a pattern
+ the very start of a pattern, and that they must be in upper case. If
+ more than one of them is present, the last one is used. They can be
+ combined with a change of newline convention, for example, a pattern
can start with:
(*ANY)(*BSR_ANYCRLF)
Unicode character properties
When PCRE is built with Unicode character property support, three addi-
- tional escape sequences that match characters with specific properties
- are available. When not in UTF-8 mode, these sequences are of course
- limited to testing characters whose codepoints are less than 256, but
+ tional escape sequences that match characters with specific properties
+ are available. When not in UTF-8 mode, these sequences are of course
+ limited to testing characters whose codepoints are less than 256, but
they do work in this mode. The extra escape sequences are:
\p{xx} a character with the xx property
\P{xx} a character without the xx property
\X an extended Unicode sequence
- The property names represented by xx above are limited to the Unicode
+ The property names represented by xx above are limited to the Unicode
script names, the general category properties, and "Any", which matches
any character (including newline). Other properties such as "InMusical-
- Symbols" are not currently supported by PCRE. Note that \P{Any} does
+ Symbols" are not currently supported by PCRE. Note that \P{Any} does
not match any characters, so always causes a match failure.
Sets of Unicode characters are defined as belonging to certain scripts.
- A character from one of these sets can be matched using a script name.
+ A character from one of these sets can be matched using a script name.
For example:
\p{Greek}
\P{Han}
- Those that are not part of an identified script are lumped together as
+ Those that are not part of an identified script are lumped together as
"Common". The current list of scripts is:
Arabic, Armenian, Balinese, Bengali, Bopomofo, Braille, Buginese,
- Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform,
+ Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform,
Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
- Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
- gana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin,
+ Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
+ gana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin,
Limbu, Linear_B, Malayalam, Mongolian, Myanmar, New_Tai_Lue, Nko,
- Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
+ Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
Runic, Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tagbanwa,
Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
- Each character has exactly one general category property, specified by
+ Each character has exactly one general category property, specified by
a two-letter abbreviation. For compatibility with Perl, negation can be
- specified by including a circumflex between the opening brace and the
+ specified by including a circumflex between the opening brace and the
property name. For example, \p{^Lu} is the same as \P{Lu}.
If only one letter is specified with \p or \P, it includes all the gen-
- eral category properties that start with that letter. In this case, in
- the absence of negation, the curly brackets in the escape sequence are
+ eral category properties that start with that letter. In this case, in
+ the absence of negation, the curly brackets in the escape sequence are
optional; these two examples have the same effect:
\p{L}
Zp Paragraph separator
Zs Space separator
- The special property L& is also supported: it matches a character that
- has the Lu, Ll, or Lt property, in other words, a letter that is not
+ The special property L& is also supported: it matches a character that
+ has the Lu, Ll, or Lt property, in other words, a letter that is not
classified as a modifier or "other".
- The Cs (Surrogate) property applies only to characters in the range
- U+D800 to U+DFFF. Such characters are not valid in UTF-8 strings (see
+ The Cs (Surrogate) property applies only to characters in the range
+ U+D800 to U+DFFF. Such characters are not valid in UTF-8 strings (see
RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
- ing has been turned off (see the discussion of PCRE_NO_UTF8_CHECK in
+ ing has been turned off (see the discussion of PCRE_NO_UTF8_CHECK in
the pcreapi page).
- The long synonyms for these properties that Perl supports (such as
- \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
+ The long synonyms for these properties that Perl supports (such as
+ \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
any of these properties with "Is".
No character that is in the Unicode table has the Cn (unassigned) prop-
erty. Instead, this property is assumed for any code point that is not
in the Unicode table.
- Specifying caseless matching does not affect these escape sequences.
+ Specifying caseless matching does not affect these escape sequences.
For example, \p{Lu} always matches only upper case letters.
- The \X escape matches any number of Unicode characters that form an
+ The \X escape matches any number of Unicode characters that form an
extended Unicode sequence. \X is equivalent to
(?>\PM\pM*)
- That is, it matches a character without the "mark" property, followed
- by zero or more characters with the "mark" property, and treats the
- sequence as an atomic group (see below). Characters with the "mark"
- property are typically accents that affect the preceding character.
- None of them have codepoints less than 256, so in non-UTF-8 mode \X
+ That is, it matches a character without the "mark" property, followed
+ by zero or more characters with the "mark" property, and treats the
+ sequence as an atomic group (see below). Characters with the "mark"
+ property are typically accents that affect the preceding character.
+ None of them have codepoints less than 256, so in non-UTF-8 mode \X
matches any one character.
- Matching characters by Unicode property is not fast, because PCRE has
- to search a structure that contains data for over fifteen thousand
+ Matching characters by Unicode property is not fast, because PCRE has
+ to search a structure that contains data for over fifteen thousand
characters. That is why the traditional escape sequences such as \d and
\w do not use Unicode properties in PCRE.
Resetting the match start
The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
- ously matched characters not to be included in the final matched
+ ously matched characters not to be included in the final matched
sequence. For example, the pattern:
foo\Kbar
- matches "foobar", but reports that it has matched "bar". This feature
- is similar to a lookbehind assertion (described below). However, in
- this case, the part of the subject before the real match does not have
- to be of fixed length, as lookbehind assertions do. The use of \K does
- not interfere with the setting of captured substrings. For example,
+ matches "foobar", but reports that it has matched "bar". This feature
+ is similar to a lookbehind assertion (described below). However, in
+ this case, the part of the subject before the real match does not have
+ to be of fixed length, as lookbehind assertions do. The use of \K does
+ not interfere with the setting of captured substrings. For example,
when the pattern
(foo)\Kbar
Simple assertions
- The final use of backslash is for certain simple assertions. An asser-
- tion specifies a condition that has to be met at a particular point in
- a match, without consuming any characters from the subject string. The
- use of subpatterns for more complicated assertions is described below.
+ The final use of backslash is for certain simple assertions. An asser-
+ tion specifies a condition that has to be met at a particular point in
+ a match, without consuming any characters from the subject string. The
+ use of subpatterns for more complicated assertions is described below.
The backslashed assertions are:
\b matches at a word boundary
\z matches only at the end of the subject
\G matches at the first matching position in the subject
- These assertions may not appear in character classes (but note that \b
+ These assertions may not appear in character classes (but note that \b
has a different meaning, namely the backspace character, inside a char-
acter class).
- A word boundary is a position in the subject string where the current
- character and the previous character do not both match \w or \W (i.e.
- one matches \w and the other matches \W), or the start or end of the
+ A word boundary is a position in the subject string where the current
+ character and the previous character do not both match \w or \W (i.e.
+ one matches \w and the other matches \W), or the start or end of the
string if the first or last character matches \w, respectively.
- The \A, \Z, and \z assertions differ from the traditional circumflex
+ The \A, \Z, and \z assertions differ from the traditional circumflex
and dollar (described in the next section) in that they only ever match
- at the very start and end of the subject string, whatever options are
- set. Thus, they are independent of multiline mode. These three asser-
+ at the very start and end of the subject string, whatever options are
+ set. Thus, they are independent of multiline mode. These three asser-
tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
- affect only the behaviour of the circumflex and dollar metacharacters.
- However, if the startoffset argument of pcre_exec() is non-zero, indi-
+ affect only the behaviour of the circumflex and dollar metacharacters.
+ However, if the startoffset argument of pcre_exec() is non-zero, indi-
cating that matching is to start at a point other than the beginning of
- the subject, \A can never match. The difference between \Z and \z is
+ the subject, \A can never match. The difference between \Z and \z is
that \Z matches before a newline at the end of the string as well as at
the very end, whereas \z matches only at the end.
- The \G assertion is true only when the current matching position is at
- the start point of the match, as specified by the startoffset argument
- of pcre_exec(). It differs from \A when the value of startoffset is
- non-zero. By calling pcre_exec() multiple times with appropriate argu-
+ The \G assertion is true only when the current matching position is at
+ the start point of the match, as specified by the startoffset argument
+ of pcre_exec(). It differs from \A when the value of startoffset is
+ non-zero. By calling pcre_exec() multiple times with appropriate argu-
ments, you can mimic Perl's /g option, and it is in this kind of imple-
mentation where \G can be useful.
- Note, however, that PCRE's interpretation of \G, as the start of the
+ Note, however, that PCRE's interpretation of \G, as the start of the
current match, is subtly different from Perl's, which defines it as the
- end of the previous match. In Perl, these can be different when the
- previously matched string was empty. Because PCRE does just one match
+ end of the previous match. In Perl, these can be different when the
+ previously matched string was empty. Because PCRE does just one match
at a time, it cannot reproduce this behaviour.
- If all the alternatives of a pattern begin with \G, the expression is
+ If all the alternatives of a pattern begin with \G, the expression is
anchored to the starting match position, and the "anchored" flag is set
in the compiled regular expression.
CIRCUMFLEX AND DOLLAR
Outside a character class, in the default matching mode, the circumflex
- character is an assertion that is true only if the current matching
- point is at the start of the subject string. If the startoffset argu-
- ment of pcre_exec() is non-zero, circumflex can never match if the
- PCRE_MULTILINE option is unset. Inside a character class, circumflex
+ character is an assertion that is true only if the current matching
+ point is at the start of the subject string. If the startoffset argu-
+ ment of pcre_exec() is non-zero, circumflex can never match if the
+ PCRE_MULTILINE option is unset. Inside a character class, circumflex
has an entirely different meaning (see below).
- Circumflex need not be the first character of the pattern if a number
- of alternatives are involved, but it should be the first thing in each
- alternative in which it appears if the pattern is ever to match that
- branch. If all possible alternatives start with a circumflex, that is,
- if the pattern is constrained to match only at the start of the sub-
- ject, it is said to be an "anchored" pattern. (There are also other
+ Circumflex need not be the first character of the pattern if a number
+ of alternatives are involved, but it should be the first thing in each
+ alternative in which it appears if the pattern is ever to match that
+ branch. If all possible alternatives start with a circumflex, that is,
+ if the pattern is constrained to match only at the start of the sub-
+ ject, it is said to be an "anchored" pattern. (There are also other
constructs that can cause a pattern to be anchored.)
- A dollar character is an assertion that is true only if the current
- matching point is at the end of the subject string, or immediately
+ A dollar character is an assertion that is true only if the current
+ matching point is at the end of the subject string, or immediately
before a newline at the end of the string (by default). Dollar need not
- be the last character of the pattern if a number of alternatives are
- involved, but it should be the last item in any branch in which it
+ be the last character of the pattern if a number of alternatives are
+ involved, but it should be the last item in any branch in which it
appears. Dollar has no special meaning in a character class.
- The meaning of dollar can be changed so that it matches only at the
- very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
+ The meaning of dollar can be changed so that it matches only at the
+ very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
compile time. This does not affect the \Z assertion.
The meanings of the circumflex and dollar characters are changed if the
- PCRE_MULTILINE option is set. When this is the case, a circumflex
- matches immediately after internal newlines as well as at the start of
- the subject string. It does not match after a newline that ends the
- string. A dollar matches before any newlines in the string, as well as
- at the very end, when PCRE_MULTILINE is set. When newline is specified
- as the two-character sequence CRLF, isolated CR and LF characters do
+ PCRE_MULTILINE option is set. When this is the case, a circumflex
+ matches immediately after internal newlines as well as at the start of
+ the subject string. It does not match after a newline that ends the
+ string. A dollar matches before any newlines in the string, as well as
+ at the very end, when PCRE_MULTILINE is set. When newline is specified
+ as the two-character sequence CRLF, isolated CR and LF characters do
not indicate newlines.
- For example, the pattern /^abc$/ matches the subject string "def\nabc"
- (where \n represents a newline) in multiline mode, but not otherwise.
- Consequently, patterns that are anchored in single line mode because
- all branches start with ^ are not anchored in multiline mode, and a
- match for circumflex is possible when the startoffset argument of
- pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
+ For example, the pattern /^abc$/ matches the subject string "def\nabc"
+ (where \n represents a newline) in multiline mode, but not otherwise.
+ Consequently, patterns that are anchored in single line mode because
+ all branches start with ^ are not anchored in multiline mode, and a
+ match for circumflex is possible when the startoffset argument of
+ pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
PCRE_MULTILINE is set.
- Note that the sequences \A, \Z, and \z can be used to match the start
- and end of the subject in both modes, and if all branches of a pattern
- start with \A it is always anchored, whether or not PCRE_MULTILINE is
+ Note that the sequences \A, \Z, and \z can be used to match the start
+ and end of the subject in both modes, and if all branches of a pattern
+ start with \A it is always anchored, whether or not PCRE_MULTILINE is
set.
FULL STOP (PERIOD, DOT)
Outside a character class, a dot in the pattern matches any one charac-
- ter in the subject string except (by default) a character that signi-
- fies the end of a line. In UTF-8 mode, the matched character may be
+ ter in the subject string except (by default) a character that signi-
+ fies the end of a line. In UTF-8 mode, the matched character may be
more than one byte long.
- When a line ending is defined as a single character, dot never matches
- that character; when the two-character sequence CRLF is used, dot does
- not match CR if it is immediately followed by LF, but otherwise it
- matches all characters (including isolated CRs and LFs). When any Uni-
- code line endings are being recognized, dot does not match CR or LF or
+ When a line ending is defined as a single character, dot never matches
+ that character; when the two-character sequence CRLF is used, dot does
+ not match CR if it is immediately followed by LF, but otherwise it
+ matches all characters (including isolated CRs and LFs). When any Uni-
+ code line endings are being recognized, dot does not match CR or LF or
any of the other line ending characters.
- The behaviour of dot with regard to newlines can be changed. If the
- PCRE_DOTALL option is set, a dot matches any one character, without
+ The behaviour of dot with regard to newlines can be changed. If the
+ PCRE_DOTALL option is set, a dot matches any one character, without
exception. If the two-character sequence CRLF is present in the subject
string, it takes two dots to match it.
- The handling of dot is entirely independent of the handling of circum-
- flex and dollar, the only relationship being that they both involve
+ The handling of dot is entirely independent of the handling of circum-
+ flex and dollar, the only relationship being that they both involve
newlines. Dot has no special meaning in a character class.
MATCHING A SINGLE BYTE
Outside a character class, the escape sequence \C matches any one byte,
- both in and out of UTF-8 mode. Unlike a dot, it always matches any
- line-ending characters. The feature is provided in Perl in order to
- match individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
- acters into individual bytes, what remains in the string may be a mal-
- formed UTF-8 string. For this reason, the \C escape sequence is best
+ both in and out of UTF-8 mode. Unlike a dot, it always matches any
+ line-ending characters. The feature is provided in Perl in order to
+ match individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
+ acters into individual bytes, what remains in the string may be a mal-
+ formed UTF-8 string. For this reason, the \C escape sequence is best
avoided.
- PCRE does not allow \C to appear in lookbehind assertions (described
- below), because in UTF-8 mode this would make it impossible to calcu-
+ PCRE does not allow \C to appear in lookbehind assertions (described
+ below), because in UTF-8 mode this would make it impossible to calcu-
late the length of the lookbehind.
An opening square bracket introduces a character class, terminated by a
closing square bracket. A closing square bracket on its own is not spe-
cial. If a closing square bracket is required as a member of the class,
- it should be the first data character in the class (after an initial
+ it should be the first data character in the class (after an initial
circumflex, if present) or escaped with a backslash.
- A character class matches a single character in the subject. In UTF-8
- mode, the character may occupy more than one byte. A matched character
+ A character class matches a single character in the subject. In UTF-8
+ mode, the character may occupy more than one byte. A matched character
must be in the set of characters defined by the class, unless the first
- character in the class definition is a circumflex, in which case the
- subject character must not be in the set defined by the class. If a
- circumflex is actually required as a member of the class, ensure it is
+ character in the class definition is a circumflex, in which case the
+ subject character must not be in the set defined by the class. If a
+ circumflex is actually required as a member of the class, ensure it is
not the first character, or escape it with a backslash.
- For example, the character class [aeiou] matches any lower case vowel,
- while [^aeiou] matches any character that is not a lower case vowel.
+ For example, the character class [aeiou] matches any lower case vowel,
+ while [^aeiou] matches any character that is not a lower case vowel.
Note that a circumflex is just a convenient notation for specifying the
- characters that are in the class by enumerating those that are not. A
- class that starts with a circumflex is not an assertion: it still con-
- sumes a character from the subject string, and therefore it fails if
+ characters that are in the class by enumerating those that are not. A
+ class that starts with a circumflex is not an assertion: it still con-
+ sumes a character from the subject string, and therefore it fails if
the current pointer is at the end of the string.
- In UTF-8 mode, characters with values greater than 255 can be included
- in a class as a literal string of bytes, or by using the \x{ escaping
+ In UTF-8 mode, characters with values greater than 255 can be included
+ in a class as a literal string of bytes, or by using the \x{ escaping
mechanism.
- When caseless matching is set, any letters in a class represent both
- their upper case and lower case versions, so for example, a caseless
- [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
- match "A", whereas a caseful version would. In UTF-8 mode, PCRE always
- understands the concept of case for characters whose values are less
- than 128, so caseless matching is always possible. For characters with
- higher values, the concept of case is supported if PCRE is compiled
- with Unicode property support, but not otherwise. If you want to use
- caseless matching for characters 128 and above, you must ensure that
- PCRE is compiled with Unicode property support as well as with UTF-8
+ When caseless matching is set, any letters in a class represent both
+ their upper case and lower case versions, so for example, a caseless
+ [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
+ match "A", whereas a caseful version would. In UTF-8 mode, PCRE always
+ understands the concept of case for characters whose values are less
+ than 128, so caseless matching is always possible. For characters with
+ higher values, the concept of case is supported if PCRE is compiled
+ with Unicode property support, but not otherwise. If you want to use
+ caseless matching for characters 128 and above, you must ensure that
+ PCRE is compiled with Unicode property support as well as with UTF-8
support.
- Characters that might indicate line breaks are never treated in any
- special way when matching character classes, whatever line-ending
- sequence is in use, and whatever setting of the PCRE_DOTALL and
+ Characters that might indicate line breaks are never treated in any
+ special way when matching character classes, whatever line-ending
+ sequence is in use, and whatever setting of the PCRE_DOTALL and
PCRE_MULTILINE options is used. A class such as [^a] always matches one
of these characters.
- The minus (hyphen) character can be used to specify a range of charac-
- ters in a character class. For example, [d-m] matches any letter
- between d and m, inclusive. If a minus character is required in a
- class, it must be escaped with a backslash or appear in a position
- where it cannot be interpreted as indicating a range, typically as the
+ The minus (hyphen) character can be used to specify a range of charac-
+ ters in a character class. For example, [d-m] matches any letter
+ between d and m, inclusive. If a minus character is required in a
+ class, it must be escaped with a backslash or appear in a position
+ where it cannot be interpreted as indicating a range, typically as the
first or last character in the class.
It is not possible to have the literal character "]" as the end charac-
- ter of a range. A pattern such as [W-]46] is interpreted as a class of
- two characters ("W" and "-") followed by a literal string "46]", so it
- would match "W46]" or "-46]". However, if the "]" is escaped with a
- backslash it is interpreted as the end of range, so [W-\]46] is inter-
- preted as a class containing a range followed by two other characters.
- The octal or hexadecimal representation of "]" can also be used to end
+ ter of a range. A pattern such as [W-]46] is interpreted as a class of
+ two characters ("W" and "-") followed by a literal string "46]", so it
+ would match "W46]" or "-46]". However, if the "]" is escaped with a
+ backslash it is interpreted as the end of range, so [W-\]46] is inter-
+ preted as a class containing a range followed by two other characters.
+ The octal or hexadecimal representation of "]" can also be used to end
a range.
- Ranges operate in the collating sequence of character values. They can
- also be used for characters specified numerically, for example
- [\000-\037]. In UTF-8 mode, ranges can include characters whose values
+ Ranges operate in the collating sequence of character values. They can
+ also be used for characters specified numerically, for example
+ [\000-\037]. In UTF-8 mode, ranges can include characters whose values
are greater than 255, for example [\x{100}-\x{2ff}].
If a range that includes letters is used when caseless matching is set,
it matches the letters in either case. For example, [W-c] is equivalent
- to [][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if
- character tables for a French locale are in use, [\xc8-\xcb] matches
- accented E characters in both cases. In UTF-8 mode, PCRE supports the
- concept of case for characters with values greater than 128 only when
+ to [][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if
+ character tables for a French locale are in use, [\xc8-\xcb] matches
+ accented E characters in both cases. In UTF-8 mode, PCRE supports the
+ concept of case for characters with values greater than 128 only when
it is compiled with Unicode property support.
- The character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
- in a character class, and add the characters that they match to the
+ The character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
+ in a character class, and add the characters that they match to the
class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
- flex can conveniently be used with the upper case character types to
- specify a more restricted set of characters than the matching lower
- case type. For example, the class [^\W_] matches any letter or digit,
+ flex can conveniently be used with the upper case character types to
+ specify a more restricted set of characters than the matching lower
+ case type. For example, the class [^\W_] matches any letter or digit,
but not underscore.
- The only metacharacters that are recognized in character classes are
- backslash, hyphen (only where it can be interpreted as specifying a
- range), circumflex (only at the start), opening square bracket (only
- when it can be interpreted as introducing a POSIX class name - see the
- next section), and the terminating closing square bracket. However,
+ The only metacharacters that are recognized in character classes are
+ backslash, hyphen (only where it can be interpreted as specifying a
+ range), circumflex (only at the start), opening square bracket (only
+ when it can be interpreted as introducing a POSIX class name - see the
+ next section), and the terminating closing square bracket. However,
escaping other non-alphanumeric characters does no harm.
POSIX CHARACTER CLASSES
Perl supports the POSIX notation for character classes. This uses names
- enclosed by [: and :] within the enclosing square brackets. PCRE also
+ enclosed by [: and :] within the enclosing square brackets. PCRE also
supports this notation. For example,
[01[:alpha:]%]
word "word" characters (same as \w)
xdigit hexadecimal digits
- The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
- and space (32). Notice that this list includes the VT character (code
+ The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
+ and space (32). Notice that this list includes the VT character (code
11). This makes "space" different to \s, which does not include VT (for
Perl compatibility).
- The name "word" is a Perl extension, and "blank" is a GNU extension
- from Perl 5.8. Another Perl extension is negation, which is indicated
+ The name "word" is a Perl extension, and "blank" is a GNU extension
+ from Perl 5.8. Another Perl extension is negation, which is indicated
by a ^ character after the colon. For example,
[12[:^digit:]]
- matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
+ matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the
POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
these are not supported, and an error is given if they are encountered.
VERTICAL BAR
- Vertical bar characters are used to separate alternative patterns. For
+ Vertical bar characters are used to separate alternative patterns. For
example, the pattern
gilbert|sullivan
- matches either "gilbert" or "sullivan". Any number of alternatives may
- appear, and an empty alternative is permitted (matching the empty
+ matches either "gilbert" or "sullivan". Any number of alternatives may
+ appear, and an empty alternative is permitted (matching the empty
string). The matching process tries each alternative in turn, from left
- to right, and the first one that succeeds is used. If the alternatives
- are within a subpattern (defined below), "succeeds" means matching the
- rest of the main pattern as well as the alternative in the subpattern.
+ to right, and the first one that succeeds is used. If the alternatives
+ are within a subpattern (defined below), "succeeds" means matching the
+ rest of the main pattern as well as the alternative in the subpattern.
INTERNAL OPTION SETTING
- The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
- PCRE_EXTENDED options (which are Perl-compatible) can be changed from
- within the pattern by a sequence of Perl option letters enclosed
+ The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
+ PCRE_EXTENDED options (which are Perl-compatible) can be changed from
+ within the pattern by a sequence of Perl option letters enclosed
between "(?" and ")". The option letters are
i for PCRE_CASELESS
For example, (?im) sets caseless, multiline matching. It is also possi-
ble to unset these options by preceding the letter with a hyphen, and a
- combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
- LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
- is also permitted. If a letter appears both before and after the
+ combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
+ LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
+ is also permitted. If a letter appears both before and after the
hyphen, the option is unset.
- The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
- can be changed in the same way as the Perl-compatible options by using
+ The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
+ can be changed in the same way as the Perl-compatible options by using
the characters J, U and X respectively.
- When an option change occurs at top level (that is, not inside subpat-
- tern parentheses), the change applies to the remainder of the pattern
+ When an option change occurs at top level (that is, not inside subpat-
+ tern parentheses), the change applies to the remainder of the pattern
that follows. If the change is placed right at the start of a pattern,
PCRE extracts it into the global options (and it will therefore show up
in data extracted by the pcre_fullinfo() function).
- An option change within a subpattern (see below for a description of
+ An option change within a subpattern (see below for a description of
subpatterns) affects only that part of the current pattern that follows
it, so
(a(?i)b)c
matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
- used). By this means, options can be made to have different settings
- in different parts of the pattern. Any changes made in one alternative
- do carry on into subsequent branches within the same subpattern. For
+ used). By this means, options can be made to have different settings
+ in different parts of the pattern. Any changes made in one alternative
+ do carry on into subsequent branches within the same subpattern. For
example,
(a(?i)b|c)
- matches "ab", "aB", "c", and "C", even though when matching "C" the
- first branch is abandoned before the option setting. This is because
- the effects of option settings happen at compile time. There would be
+ matches "ab", "aB", "c", and "C", even though when matching "C" the
+ first branch is abandoned before the option setting. This is because
+ the effects of option settings happen at compile time. There would be
some very weird behaviour otherwise.
- Note: There are other PCRE-specific options that can be set by the
- application when the compile or match functions are called. In some
- cases the pattern can contain special leading sequences to override
- what the application has set or what has been defaulted. Details are
+ Note: There are other PCRE-specific options that can be set by the
+ application when the compile or match functions are called. In some
+ cases the pattern can contain special leading sequences to override
+ what the application has set or what has been defaulted. Details are
given in the section entitled "Newline sequences" above.
cat(aract|erpillar|)
- matches one of the words "cat", "cataract", or "caterpillar". Without
- the parentheses, it would match "cataract", "erpillar" or an empty
+ matches one of the words "cat", "cataract", or "caterpillar". Without
+ the parentheses, it would match "cataract", "erpillar" or an empty
string.
- 2. It sets up the subpattern as a capturing subpattern. This means
- that, when the whole pattern matches, that portion of the subject
+ 2. It sets up the subpattern as a capturing subpattern. This means
+ that, when the whole pattern matches, that portion of the subject
string that matched the subpattern is passed back to the caller via the
- ovector argument of pcre_exec(). Opening parentheses are counted from
- left to right (starting from 1) to obtain numbers for the capturing
+ ovector argument of pcre_exec(). Opening parentheses are counted from
+ left to right (starting from 1) to obtain numbers for the capturing
subpatterns.
- For example, if the string "the red king" is matched against the pat-
+ For example, if the string "the red king" is matched against the pat-
tern
the ((red|white) (king|queen))
the captured substrings are "red king", "red", and "king", and are num-
bered 1, 2, and 3, respectively.
- The fact that plain parentheses fulfil two functions is not always
- helpful. There are often times when a grouping subpattern is required
- without a capturing requirement. If an opening parenthesis is followed
- by a question mark and a colon, the subpattern does not do any captur-
- ing, and is not counted when computing the number of any subsequent
- capturing subpatterns. For example, if the string "the white queen" is
+ The fact that plain parentheses fulfil two functions is not always
+ helpful. There are often times when a grouping subpattern is required
+ without a capturing requirement. If an opening parenthesis is followed
+ by a question mark and a colon, the subpattern does not do any captur-
+ ing, and is not counted when computing the number of any subsequent
+ capturing subpatterns. For example, if the string "the white queen" is
matched against the pattern
the ((?:red|white) (king|queen))
the captured substrings are "white queen" and "queen", and are numbered
1 and 2. The maximum number of capturing subpatterns is 65535.
- As a convenient shorthand, if any option settings are required at the
- start of a non-capturing subpattern, the option letters may appear
+ As a convenient shorthand, if any option settings are required at the
+ start of a non-capturing subpattern, the option letters may appear
between the "?" and the ":". Thus the two patterns
(?i:saturday|sunday)
(?:(?i)saturday|sunday)
match exactly the same set of strings. Because alternative branches are
- tried from left to right, and options are not reset until the end of
- the subpattern is reached, an option setting in one branch does affect
- subsequent branches, so the above patterns match "SUNDAY" as well as
+ tried from left to right, and options are not reset until the end of
+ the subpattern is reached, an option setting in one branch does affect
+ subsequent branches, so the above patterns match "SUNDAY" as well as
"Saturday".
DUPLICATE SUBPATTERN NUMBERS
Perl 5.10 introduced a feature whereby each alternative in a subpattern
- uses the same numbers for its capturing parentheses. Such a subpattern
- starts with (?| and is itself a non-capturing subpattern. For example,
+ uses the same numbers for its capturing parentheses. Such a subpattern
+ starts with (?| and is itself a non-capturing subpattern. For example,
consider this pattern:
(?|(Sat)ur|(Sun))day
- Because the two alternatives are inside a (?| group, both sets of cap-
- turing parentheses are numbered one. Thus, when the pattern matches,
- you can look at captured substring number one, whichever alternative
- matched. This construct is useful when you want to capture part, but
+ Because the two alternatives are inside a (?| group, both sets of cap-
+ turing parentheses are numbered one. Thus, when the pattern matches,
+ you can look at captured substring number one, whichever alternative
+ matched. This construct is useful when you want to capture part, but
not all, of one of a number of alternatives. Inside a (?| group, paren-
- theses are numbered as usual, but the number is reset at the start of
- each branch. The numbers of any capturing buffers that follow the sub-
- pattern start after the highest number used in any branch. The follow-
- ing example is taken from the Perl documentation. The numbers under-
+ theses are numbered as usual, but the number is reset at the start of
+ each branch. The numbers of any capturing buffers that follow the sub-
+ pattern start after the highest number used in any branch. The follow-
+ ing example is taken from the Perl documentation. The numbers under-
neath show in which buffer the captured content will be stored.
# before ---------------branch-reset----------- after
/ ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
# 1 2 2 3 2 3 4
- A backreference or a recursive call to a numbered subpattern always
+ A backreference or a recursive call to a numbered subpattern always
refers to the first one in the pattern with the given number.
- An alternative approach to using this "branch reset" feature is to use
+ An alternative approach to using this "branch reset" feature is to use
duplicate named subpatterns, as described in the next section.
NAMED SUBPATTERNS
- Identifying capturing parentheses by number is simple, but it can be
- very hard to keep track of the numbers in complicated regular expres-
- sions. Furthermore, if an expression is modified, the numbers may
- change. To help with this difficulty, PCRE supports the naming of sub-
+ Identifying capturing parentheses by number is simple, but it can be
+ very hard to keep track of the numbers in complicated regular expres-
+ sions. Furthermore, if an expression is modified, the numbers may
+ change. To help with this difficulty, PCRE supports the naming of sub-
patterns. This feature was not added to Perl until release 5.10. Python
- had the feature earlier, and PCRE introduced it at release 4.0, using
- the Python syntax. PCRE now supports both the Perl and the Python syn-
+ had the feature earlier, and PCRE introduced it at release 4.0, using
+ the Python syntax. PCRE now supports both the Perl and the Python syn-
tax.
- In PCRE, a subpattern can be named in one of three ways: (?<name>...)
- or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
+ In PCRE, a subpattern can be named in one of three ways: (?<name>...)
+ or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
to capturing parentheses from other parts of the pattern, such as back-
- references, recursion, and conditions, can be made by name as well as
+ references, recursion, and conditions, can be made by name as well as
by number.
- Names consist of up to 32 alphanumeric characters and underscores.
- Named capturing parentheses are still allocated numbers as well as
- names, exactly as if the names were not present. The PCRE API provides
+ Names consist of up to 32 alphanumeric characters and underscores.
+ Named capturing parentheses are still allocated numbers as well as
+ names, exactly as if the names were not present. The PCRE API provides
function calls for extracting the name-to-number translation table from
a compiled pattern. There is also a convenience function for extracting
a captured substring by name.
- By default, a name must be unique within a pattern, but it is possible
+ By default, a name must be unique within a pattern, but it is possible
to relax this constraint by setting the PCRE_DUPNAMES option at compile
- time. This can be useful for patterns where only one instance of the
- named parentheses can match. Suppose you want to match the name of a
- weekday, either as a 3-letter abbreviation or as the full name, and in
+ time. This can be useful for patterns where only one instance of the
+ named parentheses can match. Suppose you want to match the name of a
+ weekday, either as a 3-letter abbreviation or as the full name, and in
both cases you want to extract the abbreviation. This pattern (ignoring
the line breaks) does the job:
(?<DN>Thu)(?:rsday)?|
(?<DN>Sat)(?:urday)?
- There are five capturing substrings, but only one is ever set after a
+ There are five capturing substrings, but only one is ever set after a
match. (An alternative way of solving this problem is to use a "branch
reset" subpattern, as described in the previous section.)
- The convenience function for extracting the data by name returns the
- substring for the first (and in this example, the only) subpattern of
- that name that matched. This saves searching to find which numbered
- subpattern it was. If you make a reference to a non-unique named sub-
- pattern from elsewhere in the pattern, the one that corresponds to the
- lowest number is used. For further details of the interfaces for han-
+ The convenience function for extracting the data by name returns the
+ substring for the first (and in this example, the only) subpattern of
+ that name that matched. This saves searching to find which numbered
+ subpattern it was. If you make a reference to a non-unique named sub-
+ pattern from elsewhere in the pattern, the one that corresponds to the
+ lowest number is used. For further details of the interfaces for han-
dling named subpatterns, see the pcreapi documentation.
REPETITION
- Repetition is specified by quantifiers, which can follow any of the
+ Repetition is specified by quantifiers, which can follow any of the
following items:
a literal data character
a back reference (see next section)
a parenthesized subpattern (unless it is an assertion)
- The general repetition quantifier specifies a minimum and maximum num-
- ber of permitted matches, by giving the two numbers in curly brackets
- (braces), separated by a comma. The numbers must be less than 65536,
+ The general repetition quantifier specifies a minimum and maximum num-
+ ber of permitted matches, by giving the two numbers in curly brackets
+ (braces), separated by a comma. The numbers must be less than 65536,
and the first must be less than or equal to the second. For example:
z{2,4}
- matches "zz", "zzz", or "zzzz". A closing brace on its own is not a
- special character. If the second number is omitted, but the comma is
- present, there is no upper limit; if the second number and the comma
- are both omitted, the quantifier specifies an exact number of required
+ matches "zz", "zzz", or "zzzz". A closing brace on its own is not a
+ special character. If the second number is omitted, but the comma is
+ present, there is no upper limit; if the second number and the comma
+ are both omitted, the quantifier specifies an exact number of required
matches. Thus
[aeiou]{3,}
\d{8}
- matches exactly 8 digits. An opening curly bracket that appears in a
- position where a quantifier is not allowed, or one that does not match
- the syntax of a quantifier, is taken as a literal character. For exam-
+ matches exactly 8 digits. An opening curly bracket that appears in a
+ position where a quantifier is not allowed, or one that does not match
+ the syntax of a quantifier, is taken as a literal character. For exam-
ple, {,6} is not a quantifier, but a literal string of four characters.
- In UTF-8 mode, quantifiers apply to UTF-8 characters rather than to
+ In UTF-8 mode, quantifiers apply to UTF-8 characters rather than to
individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
acters, each of which is represented by a two-byte sequence. Similarly,
when Unicode property support is available, \X{3} matches three Unicode
- extended sequences, each of which may be several bytes long (and they
+ extended sequences, each of which may be several bytes long (and they
may be of different lengths).
The quantifier {0} is permitted, causing the expression to behave as if
- the previous item and the quantifier were not present.
+ the previous item and the quantifier were not present. This may be use-
+ ful for subpatterns that are referenced as subroutines from elsewhere
+ in the pattern. Items other than subpatterns that have a {0} quantifier
+ are omitted from the compiled pattern.
For convenience, the three most common quantifiers have single-charac-
ter abbreviations:
processing option does not affect the called subpattern.
+ONIGURUMA SUBROUTINE SYNTAX
+
+ For compatibility with Oniguruma, the non-Perl syntax \g followed by a
+ name or a number enclosed either in angle brackets or single quotes, is
+ an alternative syntax for referencing a subpattern as a subroutine,
+ possibly recursively. Here are two of the examples used above, rewrit-
+ ten using this syntax:
+
+ (?<pn> \( ( (?>[^()]+) | \g<pn> )* \) )
+ (sens|respons)e and \g'1'ibility
+
+ PCRE supports an extension to Oniguruma: if a number is preceded by a
+ plus or a minus sign it is taken as a relative reference. For example:
+
+ (abc)(?i:\g<-1>)
+
+ Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not
+ synonymous. The former is a back reference; the latter is a subroutine
+ call.
+
+
CALLOUTS
Perl has a feature whereby using the sequence (?{...}) causes arbitrary
- Perl code to be obeyed in the middle of matching a regular expression.
+ Perl code to be obeyed in the middle of matching a regular expression.
This makes it possible, amongst other things, to extract different sub-
strings that match the same pair of parentheses when there is a repeti-
tion.
PCRE provides a similar feature, but of course it cannot obey arbitrary
Perl code. The feature is called "callout". The caller of PCRE provides
- an external function by putting its entry point in the global variable
- pcre_callout. By default, this variable contains NULL, which disables
+ an external function by putting its entry point in the global variable
+ pcre_callout. By default, this variable contains NULL, which disables
all calling out.
- Within a regular expression, (?C) indicates the points at which the
- external function is to be called. If you want to identify different
- callout points, you can put a number less than 256 after the letter C.
- The default value is zero. For example, this pattern has two callout
+ Within a regular expression, (?C) indicates the points at which the
+ external function is to be called. If you want to identify different
+ callout points, you can put a number less than 256 after the letter C.
+ The default value is zero. For example, this pattern has two callout
points:
(?C1)abc(?C2)def
If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are
- automatically installed before each item in the pattern. They are all
+ automatically installed before each item in the pattern. They are all
numbered 255.
During matching, when PCRE reaches a callout point (and pcre_callout is
- set), the external function is called. It is provided with the number
- of the callout, the position in the pattern, and, optionally, one item
- of data originally supplied by the caller of pcre_exec(). The callout
- function may cause matching to proceed, to backtrack, or to fail alto-
+ set), the external function is called. It is provided with the number
+ of the callout, the position in the pattern, and, optionally, one item
+ of data originally supplied by the caller of pcre_exec(). The callout
+ function may cause matching to proceed, to backtrack, or to fail alto-
gether. A complete description of the interface to the callout function
is given in the pcrecallout documentation.
BACKTRACKING CONTROL
- Perl 5.10 introduced a number of "Special Backtracking Control Verbs",
+ Perl 5.10 introduced a number of "Special Backtracking Control Verbs",
which are described in the Perl documentation as "experimental and sub-
- ject to change or removal in a future version of Perl". It goes on to
- say: "Their usage in production code should be noted to avoid problems
+ ject to change or removal in a future version of Perl". It goes on to
+ say: "Their usage in production code should be noted to avoid problems
during upgrades." The same remarks apply to the PCRE features described
in this section.
- Since these verbs are specifically related to backtracking, they can be
- used only when the pattern is to be matched using pcre_exec(), which
- uses a backtracking algorithm. They cause an error if encountered by
- pcre_dfa_exec().
+ Since these verbs are specifically related to backtracking, most of
+ them can be used only when the pattern is to be matched using
+ pcre_exec(), which uses a backtracking algorithm. With the exception of
+ (*FAIL), which behaves like a failing negative assertion, they cause an
+ error if encountered by pcre_dfa_exec().
The new verbs make use of what was previously invalid syntax: an open-
ing parenthesis followed by an asterisk. In Perl, they are generally of
REVISION
- Last updated: 17 September 2007
- Copyright (c) 1997-2007 University of Cambridge.
+ Last updated: 19 April 2008
+ Copyright (c) 1997-2008 University of Cambridge.
------------------------------------------------------------------------------
(?-n) call subpattern by relative number
(?&name) call subpattern by name (Perl)
(?P>name) call subpattern by name (Python)
+ \g<name> call subpattern by name (Oniguruma)
+ \g'name' call subpattern by name (Oniguruma)
+ \g<n> call subpattern by absolute number (Oniguruma)
+ \g'n' call subpattern by absolute number (Oniguruma)
+ \g<+n> call subpattern by relative number (PCRE extension)
+ \g'+n' call subpattern by relative number (PCRE extension)
+ \g<-n> call subpattern by relative number (PCRE extension)
+ \g'-n' call subpattern by relative number (PCRE extension)
CONDITIONAL PATTERNS
REVISION
- Last updated: 14 November 2007
- Copyright (c) 1997-2007 University of Cambridge.
+ Last updated: 09 April 2008
+ Copyright (c) 1997-2008 University of Cambridge.
------------------------------------------------------------------------------
MATCHING A PATTERN
The function regexec() is called to match a compiled pattern preg
- against a given string, which is terminated by a zero byte, subject to
- the options in eflags. These can be:
+ against a given string, which is by default terminated by a zero byte
+ (but see REG_STARTEND below), subject to the options in eflags. These
+ can be:
REG_NOTBOL
The PCRE_NOTEOL option is set when calling the underlying PCRE matching
function.
+ REG_STARTEND
+
+ The string is considered to start at string + pmatch[0].rm_so and to
+ have a terminating NUL located at string + pmatch[0].rm_eo (there need
+ not actually be a NUL at that location), regardless of the value of
+ nmatch. This is a BSD extension, compatible with but not specified by
+ IEEE Standard 1003.2 (POSIX.2), and should be used with caution in
+ software intended to be portable to other systems. Note that a non-zero
+ rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
+ of the string, not how it is matched.
+
If the pattern was compiled with the REG_NOSUB flag, no data about any
matched strings is returned. The nmatch and pmatch arguments of
regexec() are ignored.
REVISION
- Last updated: 06 March 2007
- Copyright (c) 1997-2007 University of Cambridge.
+ Last updated: 05 April 2008
+ Copyright (c) 1997-2008 University of Cambridge.
------------------------------------------------------------------------------
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