The Perl regular expression syntax is based on that used by the
programming language Perl . Perl regular expressions are the
-default behavior in Boost.Regex or you can pass the flag =perl= to the
+default behavior in Boost.Regex or you can pass the flag [^perl] to the
[basic_regex] constructor, for example:
// e1 is a case sensitive Perl regular expression:
any single character except:
* The NULL character when the [link boost_regex.ref.match_flag_type flag
- =match_not_dot_null=] is passed to the matching algorithms.
+ [^match_not_dot_null]] is passed to the matching algorithms.
* The newline character when the [link boost_regex.ref.match_flag_type
- flag =match_not_dot_newline=] is passed to
+ flag [^match_not_dot_newline]] is passed to
the matching algorithms.
[h4 Anchors]
[h4 Marked sub-expressions]
-A section beginning =(= and ending =)= acts as a marked sub-expression.
+A section beginning [^(] and ending [^)] acts as a marked sub-expression.
Whatever matched the sub-expression is split out in a separate field by
the matching algorithms. Marked sub-expressions can also repeated, or
referred to by a back-reference.
expression, but has the side-effect of spitting out an extra field in
the result. As an alternative you can lexically group part of a
regular expression, without generating a marked sub-expression by using
-=(?:= and =)= , for example =(?:ab)+= will repeat =ab= without splitting
+[^(?:] and [^)] , for example [^(?:ab)+] will repeat [^ab] without splitting
out any separate sub-expressions.
[h4 Repeats]
Any atom (a single character, a marked sub-expression, or a character class)
-can be repeated with the =*=, =+=, =?=, and ={}= operators.
+can be repeated with the [^*], [^+], [^?], and [^{}] operators.
-The =*= operator will match the preceding atom zero or more times,
-for example the expression =a*b= will match any of the following:
+The [^*] operator will match the preceding atom zero or more times,
+for example the expression [^a*b] will match any of the following:
b
ab
aaaaaaaab
-The =+= operator will match the preceding atom one or more times, for
-example the expression =a+b= will match any of the following:
+The [^+] operator will match the preceding atom one or more times, for
+example the expression [^a+b] will match any of the following:
ab
aaaaaaaab
b
-The =?= operator will match the preceding atom zero or one times, for
+The [^?] operator will match the preceding atom zero or one times, for
example the expression ca?b will match any of the following:
cb
An atom can also be repeated with a bounded repeat:
-=a{n}= Matches 'a' repeated exactly n times.
+[^a{n}] Matches 'a' repeated exactly n times.
-=a{n,}= Matches 'a' repeated n or more times.
+[^a{n,}] Matches 'a' repeated n or more times.
-=a{n, m}= Matches 'a' repeated between n and m times inclusive.
+[^a{n, m}] Matches 'a' repeated between n and m times inclusive.
For example:
a
aaaa
+Note that the "{" and "}" characters will treated as ordinary literals when used
+in a context that is not a repeat: this matches Perl 5.x behavior. For example in
+the expressions "ab{1", "ab1}" and "a{b}c" the curly brackets are all treated as
+literals and ['no error will be raised].
+
It is an error to use a repeat operator, if the preceding construct can not
be repeated, for example:
a(*)
-Will raise an error, as there is nothing for the =*= operator to be applied to.
+Will raise an error, as there is nothing for the [^*] operator to be applied to.
[h4 Non greedy repeats]
much input as possible. There are non-greedy versions available that will
consume as little input as possible while still producing a match.
-=*?= Matches the previous atom zero or more times, while consuming as little
+[^*?] Matches the previous atom zero or more times, while consuming as little
input as possible.
-=+?= Matches the previous atom one or more times, while consuming as
+[^+?] Matches the previous atom one or more times, while consuming as
little input as possible.
-=??= Matches the previous atom zero or one times, while consuming
+[^??] Matches the previous atom zero or one times, while consuming
as little input as possible.
-={n,}?= Matches the previous atom n or more times, while consuming as
+[^{n,}?] Matches the previous atom n or more times, while consuming as
little input as possible.
-={n,m}?= Matches the previous atom between n and m times, while
+[^{n,m}?] Matches the previous atom between n and m times, while
consuming as little input as possible.
[h4 Possessive repeats]
By default when a repeated pattern does not match then the engine will backtrack until
-a match is found. However, this behaviour can sometime be undesireable so there are
+a match is found. However, this behaviour can sometime be undesireble so there are
also "possessive" repeats: these match as much as possible and do not then allow
backtracking if the rest of the expression fails to match.
-=*+= Matches the previous atom zero or more times, while giving nothing back.
+[^*+] Matches the previous atom zero or more times, while giving nothing back.
-=++= Matches the previous atom one or more times, while giving nothing back.
+[^++] Matches the previous atom one or more times, while giving nothing back.
-=?+= Matches the previous atom zero or one times, while giving nothing back.
+[^?+] Matches the previous atom zero or one times, while giving nothing back.
-={n,}+= Matches the previous atom n or more times, while giving nothing back.
+[^{n,}+] Matches the previous atom n or more times, while giving nothing back.
-={n,m}+= Matches the previous atom between n and m times, while giving nothing back.
+[^{n,m}+] Matches the previous atom between n and m times, while giving nothing back.
[h4 Back references]
[table
[[Escape][Meaning]]
-[[=\g1=][Match whatever matched sub-expression 1]]
-[[=\g{1}=][Match whatever matched sub-expression 1: this form allows for safer
- parsing of the expression in cases like =\g{1}2= or for indexes higher than 9 as in =\g{1234}=]]
-[[=\g-1=][Match whatever matched the last opened sub-expression]]
-[[=\g{-2}=][Match whatever matched the last but one opened sub-expression]]
-[[=\g{one}=][Match whatever matched the sub-expression named "one"]]
+[[[^\g1]][Match whatever matched sub-expression 1]]
+[[[^\g{1}]][Match whatever matched sub-expression 1: this form allows for safer
+ parsing of the expression in cases like [^\g{1}2] or for indexes higher than 9 as in [^\g{1234}]]]
+[[[^\g-1]][Match whatever matched the last opened sub-expression]]
+[[[^\g{-2}]][Match whatever matched the last but one opened sub-expression]]
+[[[^\g{one}]][Match whatever matched the sub-expression named "one"]]
]
Finally the \k escape can be used to refer to named subexpressions, for example [^\k<two>] will match
[h4 Alternation]
-The =|= operator will match either of its arguments, so for example:
-=abc|def= will match either "abc" or "def".
+The [^|] operator will match either of its arguments, so for example:
+[^abc|def] will match either "abc" or "def".
-Parenthesis can be used to group alternations, for example: =ab(d|ef)=
+Parenthesis can be used to group alternations, for example: [^ab(d|ef)]
will match either of "abd" or "abef".
Empty alternatives are not allowed (these are almost always a mistake), but
-if you really want an empty alternative use =(?:)= as a placeholder, for example:
+if you really want an empty alternative use [^(?:)] as a placeholder, for example:
-=|abc= is not a valid expression, but
+[^|abc] is not a valid expression, but
-=(?:)|abc= is and is equivalent, also the expression:
+[^(?:)|abc] is and is equivalent, also the expression:
-=(?:abc)??= has exactly the same effect.
+[^(?:abc)??] has exactly the same effect.
[h4 Character sets]
-A character set is a bracket-expression starting with =[= and ending with =]=,
+A character set is a bracket-expression starting with [^[] and ending with [^]],
it defines a set of characters, and matches any single character that is a
member of that set.
[h5 Single characters]
-For example =[abc]=, will match any of the characters 'a', 'b', or 'c'.
+For example [^\[abc\]], will match any of the characters 'a', 'b', or 'c'.
[h5 Character ranges]
-For example =[a-c]= will match any single character in the range 'a' to 'c'.
+For example [^\[a-c\]] will match any single character in the range 'a' to 'c'.
By default, for Perl regular expressions, a character x is within the
range y to z, if the code point of the character lies within the codepoints of
the endpoints of the range. Alternatively, if you set the
-[link boost_regex.ref.syntax_option_type.syntax_option_type_perl =collate= flag]
+[link boost_regex.ref.syntax_option_type.syntax_option_type_perl [^collate] flag]
when constructing the regular expression, then ranges are locale sensitive.
[h5 Negation]
If the bracket-expression begins with the ^ character, then it matches the
-complement of the characters it contains, for example =[^a-c]= matches
-any character that is not in the range =a-c=.
+complement of the characters it contains, for example [^\[^a-c\]] matches
+any character that is not in the range [^a-c].
[h5 Character classes]
[[.NUL.]]
-matches a =\0= character.
+matches a [^\0] character.
[h5 Equivalence classes]
[table
[[Escape][Character]]
-[[=\a=][=\a=]]
-[[=\e=][=0x1B=]]
-[[=\f=][=\f=]]
-[[=\n=][=\n=]]
-[[=\r=][=\r=]]
-[[=\t=][=\t=]]
-[[=\v=][=\v=]]
-[[=\b=][=\b= (but only inside a character class declaration).]]
-[[=\cX=][An ASCII escape sequence - the character whose code point is X % 32]]
-[[=\xdd=][A hexadecimal escape sequence - matches the single character whose
+[[[^\a]][[^\a]]]
+[[[^\e]][[^0x1B]]]
+[[[^\f]][[^\f]]]
+[[[^\n]][[^\n]]]
+[[[^\r]][[^\r]]]
+[[[^\t]][[^\t]]]
+[[[^\v]][[^\v]]]
+[[[^\b]][[^\b] (but only inside a character class declaration).]]
+[[[^\cX]][An ASCII escape sequence - the character whose code point is X % 32]]
+[[[^\xdd]][A hexadecimal escape sequence - matches the single character whose
code point is 0xdd.]]
-[[=\x{dddd}=][A hexadecimal escape sequence - matches the single character whose
+[[[^\x{dddd}]][A hexadecimal escape sequence - matches the single character whose
code point is 0xdddd.]]
-[[=\0ddd=][An octal escape sequence - matches the single character whose
+[[[^\0ddd]][An octal escape sequence - matches the single character whose
code point is 0ddd.]]
-[[=\N{name}=][Matches the single character which has the
+[[[^\N{name}]][Matches the single character which has the
[link boost_regex.syntax.collating_names symbolic name] /name/.
- For example =\N{newline}= matches the single character \\n.]]
+ For example [^\N{newline}] matches the single character \\n.]]
]
[h5 "Single character" character classes:]
[[`\P{Name}`][Matches any character that does not have the property Name.][`[^[:Name:]]`]]
]
-For example =\pd= matches any "digit" character, as does =\p{digit}=.
+For example [^\pd] matches any "digit" character, as does [^\p{digit}].
[h5 Word Boundaries]
The following escape sequences match the boundaries of words:
-=\<= Matches the start of a word.
+[^\<] Matches the start of a word.
-=\>= Matches the end of a word.
+[^\>] Matches the end of a word.
-=\b= Matches a word boundary (the start or end of a word).
+[^\b] Matches a word boundary (the start or end of a word).
-=\B= Matches only when not at a word boundary.
+[^\B] Matches only when not at a word boundary.
[h5 Buffer boundaries]
\\' Matches at the end of a buffer only.
-\\A Matches at the start of a buffer only (the same as =\\\`=).
+\\A Matches at the start of a buffer only (the same as [^\\\`]).
-\\z Matches at the end of a buffer only (the same as =\\'=).
+\\z Matches at the end of a buffer only (the same as [^\\']).
\\Z Matches a zero-width assertion consisting of an optional sequence of newlines at the end of a buffer:
equivalent to the regular expression [^(?=\\v*\\z)]. Note that this is subtly different from Perl which
[h5 Continuation Escape]
-The sequence =\G= matches only at the end of the last match found, or at
+The sequence [^\G] matches only at the end of the last match found, or at
the start of the text being matched if no previous match was found.
This escape useful if you're iterating over the matches contained within a
text, and you want each subsequence match to start where the last one ended.
[h5 Quoting escape]
-The escape sequence =\Q= begins a "quoted sequence": all the subsequent characters
+The escape sequence [^\Q] begins a "quoted sequence": all the subsequent characters
are treated as literals, until either the end of the regular expression or \\E
-is found. For example the expression: =\Q\*+\Ea+= would match either of:
+is found. For example the expression: [^\Q\*+\Ea+] would match either of:
\*+a
\*+aaa
[h5 Unicode escapes]
-=\C= Matches a single code point: in Boost regex this has exactly the
+[^\C] Matches a single code point: in Boost regex this has exactly the
same effect as a "." operator.
-=\X= Matches a combining character sequence: that is any non-combining
+[^\X] Matches a combining character sequence: that is any non-combining
character followed by a sequence of zero or more combining characters.
[h5 Matching Line Endings]
-The escape sequence =\R= matches any line ending character sequence, specifically it is identical to
+The escape sequence [^\R] matches any line ending character sequence, specifically it is identical to
the expression [^(?>\x0D\x0A?|\[\x0A-\x0C\x85\x{2028}\x{2029}\])].
[h5 Keeping back some text]
-=\K= Resets the start location of $0 to the current text position: in other words everything to the
+[^\K] Resets the start location of $0 to the current text position: in other words everything to the
left of \K is "kept back" and does not form part of the regular expression match. $` is updated
accordingly.
-For example =foo\Kbar= matched against the text "foobar" would return the match "bar" for $0 and "foo"
+For example [^foo\Kbar] matched against the text "foobar" would return the match "bar" for $0 and "foo"
for $`. This can be used to simulate variable width lookbehind assertions.
[h5 Any other escape]
[h4 Perl Extended Patterns]
-Perl-specific extensions to the regular expression syntax all start with =(?=.
+Perl-specific extensions to the regular expression syntax all start with [^(?].
[h5 Named Subexpressions]
(?<NAME>expression)
-Which can be then be refered to by the name /NAME/. Alternatively you can delimit the name
+Which can be then be referred to by the name /NAME/. Alternatively you can delimit the name
using 'NAME' as in:
(?'NAME'expression)
-These named subexpressions can be refered to in a backreference using either [^\g{NAME}] or [^\k<NAME>]
-and can also be refered to by name in a [perl_format] format string for search and replace operations, or in the
+These named subexpressions can be referred to in a backreference using either [^\g{NAME}] or [^\k<NAME>]
+and can also be referred to by name in a [perl_format] format string for search and replace operations, or in the
[match_results] member functions.
[h5 Comments]
-=(?# ... )= is treated as a comment, it's contents are ignored.
+[^(?# ... )] is treated as a comment, it's contents are ignored.
[h5 Modifiers]
-=(?imsx-imsx ... )= alters which of the perl modifiers are in effect within
+[^(?imsx-imsx ... )] alters which of the perl modifiers are in effect within
the pattern, changes take effect from the point that the block is first seen
-and extend to any enclosing =)=. Letters before a '-' turn that perl
+and extend to any enclosing [^)]. Letters before a '-' turn that perl
modifier on, letters afterward, turn it off.
-=(?imsx-imsx:pattern)= applies the specified modifiers to pattern only.
+[^(?imsx-imsx:pattern)] applies the specified modifiers to pattern only.
[h5 Non-marking groups]
-=(?:pattern)= lexically groups pattern, without generating an additional
+[^(?:pattern)] lexically groups pattern, without generating an additional
sub-expression.
[h5 Branch reset]
-=(?|pattern)= resets the subexpression count at the start of each "|" alternative within /pattern/.
+[^(?|pattern)] resets the subexpression count at the start of each "|" alternative within /pattern/.
The sub-expression count following this construct is that of whichever branch had the largest number of
sub-expressions. This construct is useful when you want to capture one of a number of alternative matches
[^(?=pattern)] consumes zero characters, only if pattern matches.
-=(?!pattern)= consumes zero characters, only if pattern does not match.
+[^(?!pattern)] consumes zero characters, only if pattern does not match.
Lookahead is typically used to create the logical AND of two regular
expressions, for example if a password must contain a lower case letter,
against the characters preceding the current position (pattern must be
of fixed length).
-=(?<!pattern)= consumes zero characters, only if pattern could not be
+[^(?<!pattern)] consumes zero characters, only if pattern could not be
matched against the characters preceding the current position (pattern must
be of fixed length).
[h5 Independent sub-expressions]
-=(?>pattern)= /pattern/ is matched independently of the surrounding patterns,
+[^(?>pattern)] /pattern/ is matched independently of the surrounding patterns,
the expression will never backtrack into /pattern/. Independent sub-expressions
are typically used to improve performance; only the best possible match
for pattern will be considered, if this doesn't allow the expression as a
[^(?['N]) (?-['N]) (?+['N]) (?R) (?0) (?&NAME)]
-=(?R)= and =(?0)= recurse to the start of the entire pattern.
+[^(?R)] and [^(?0)] recurse to the start of the entire pattern.
-[^(?['N])] executes sub-expression /N/ recursively, for example =(?2)= will recurse to sub-expression 2.
+[^(?['N])] executes sub-expression /N/ recursively, for example [^(?2)] will recurse to sub-expression 2.
-[^(?-['N])] and [^(?+['N])] are relative recursions, so for example =(?-1)= recurses to the last sub-expression to be declared,
-and =(?+1)= recurses to the next sub-expression to be declared.
+[^(?-['N])] and [^(?+['N])] are relative recursions, so for example [^(?-1)] recurses to the last sub-expression to be declared,
+and [^(?+1)] recurses to the next sub-expression to be declared.
[^(?&NAME)] recurses to named sub-expression ['NAME].
[h5 Conditional Expressions]
-=(?(condition)yes-pattern|no-pattern)= attempts to match /yes-pattern/ if
+[^(?(condition)yes-pattern|no-pattern)] attempts to match /yes-pattern/ if
the /condition/ is true, otherwise attempts to match /no-pattern/.
-=(?(condition)yes-pattern)= attempts to match /yes-pattern/ if the /condition/
+[^(?(condition)yes-pattern)] attempts to match /yes-pattern/ if the /condition/
is true, otherwise matches the NULL string.
/condition/ may be either: a forward lookahead assert, the index of
* [^(?(?\=assert)yes-pattern|no-pattern)] Executes /yes-pattern/ if the forward look-ahead assert matches, otherwise
executes /no-pattern/.
-* =(?(?!assert)yes-pattern|no-pattern)= Executes /yes-pattern/ if the forward look-ahead assert does not match, otherwise
+* [^(?(?!assert)yes-pattern|no-pattern)] Executes /yes-pattern/ if the forward look-ahead assert does not match, otherwise
executes /no-pattern/.
-* =(?(['N])yes-pattern|no-pattern)= Executes /yes-pattern/ if subexpression /N/ has been matched, otherwise
+* [^(?(['N])yes-pattern|no-pattern)] Executes /yes-pattern/ if subexpression /N/ has been matched, otherwise
executes /no-pattern/.
-* =(?(<['name]>)yes-pattern|no-pattern)= Executes /yes-pattern/ if named subexpression /name/ has been matched, otherwise
+* [^(?(<['name]>)yes-pattern|no-pattern)] Executes /yes-pattern/ if named subexpression /name/ has been matched, otherwise
executes /no-pattern/.
-* =(?('['name]')yes-pattern|no-pattern)= Executes /yes-pattern/ if named subexpression /name/ has been matched, otherwise
+* [^(?('['name]')yes-pattern|no-pattern)] Executes /yes-pattern/ if named subexpression /name/ has been matched, otherwise
executes /no-pattern/.
-* =(?(R)yes-pattern|no-pattern)= Executes /yes-pattern/ if we are executing inside a recursion, otherwise
+* [^(?(R)yes-pattern|no-pattern)] Executes /yes-pattern/ if we are executing inside a recursion, otherwise
executes /no-pattern/.
* [^(?(R['N])yes-pattern|no-pattern)] Executes /yes-pattern/ if we are executing inside a recursion to sub-expression /N/, otherwise
executes /no-pattern/.
* [^(?(R&['name])yes-pattern|no-pattern)] Executes /yes-pattern/ if we are executing inside a recursion to named sub-expression /name/, otherwise
executes /no-pattern/.
* [^(?(DEFINE)never-exectuted-pattern)] Defines a block of code that is never executed and matches no characters:
-this is usually used to define one or more named sub-expressions which are refered to from elsewhere in the pattern.
+this is usually used to define one or more named sub-expressions which are referred to from elsewhere in the pattern.
[h4 Operator precedence]
The order of precedence for of operators is as follows:
# Collation-related bracket symbols `[==] [::] [..]`
-# Escaped characters =\=
+# Escaped characters [^\]
# Character set (bracket expression) `[]`
-# Grouping =()=
-# Single-character-ERE duplication =* + ? {m,n}=
+# Grouping [^()]
+# Single-character-ERE duplication [^* + ? {m,n}]
# Concatenation
# Anchoring ^$
# Alternation |
[table
[[Construct][What gets matched]]
-[[=AtomA AtomB=][Locates the best match for /AtomA/ that has a following match for /AtomB/.]]
-[[=Expression1 | Expression2=][If /Expresion1/ can be matched then returns that match,
+[[[^AtomA AtomB]][Locates the best match for /AtomA/ that has a following match for /AtomB/.]]
+[[[^Expression1 | Expression2]][If /Expresion1/ can be matched then returns that match,
otherwise attempts to match /Expression2/.]]
-[[=S{N}=][Matches /S/ repeated exactly N times.]]
-[[=S{N,M}=][Matches S repeated between N and M times, and as many times as possible.]]
-[[=S{N,M}?=][Matches S repeated between N and M times, and as few times as possible.]]
-[[=S?, S*, S+=][The same as =S{0,1}=, =S{0,UINT_MAX}=, =S{1,UINT_MAX}= respectively.]]
-[[=S??, S*?, S+?=][The same as =S{0,1}?=, =S{0,UINT_MAX}?=, =S{1,UINT_MAX}?= respectively.]]
-[[=(?>S)=][Matches the best match for /S/, and only that.]]
+[[[^S{N}]][Matches /S/ repeated exactly N times.]]
+[[[^S{N,M}]][Matches S repeated between N and M times, and as many times as possible.]]
+[[[^S{N,M}?]][Matches S repeated between N and M times, and as few times as possible.]]
+[[[^S?, S*, S+]][The same as [^S{0,1}], [^S{0,UINT_MAX}], [^S{1,UINT_MAX}] respectively.]]
+[[[^S??, S*?, S+?]][The same as [^S{0,1}?], [^S{0,UINT_MAX}?], [^S{1,UINT_MAX}?] respectively.]]
+[[[^(?>S)]][Matches the best match for /S/, and only that.]]
[[[^(?=S), (?<=S)]][Matches only the best match for /S/ (this is only
visible if there are capturing parenthesis within /S/).]]
-[[=(?!S), (?<!S)=][Considers only whether a match for S exists or not.]]
-[[=(?(condition)yes-pattern | no-pattern)=][If condition is true, then
+[[[^(?!S), (?<!S)]][Considers only whether a match for S exists or not.]]
+[[[^(?(condition)yes-pattern | no-pattern)]][If condition is true, then
only yes-pattern is considered, otherwise only no-pattern is considered.]]
]
[h3 Variations]
-The [link boost_regex.ref.syntax_option_type.syntax_option_type_perl options =normal=,
-=ECMAScript=, =JavaScript= and =JScript=] are all synonyms for
-=perl=.
+The [link boost_regex.ref.syntax_option_type.syntax_option_type_perl options [^normal],
+[^ECMAScript], [^JavaScript] and [^JScript]] are all synonyms for
+[^perl].
[h3 Options]
There are a [link boost_regex.ref.syntax_option_type.syntax_option_type_perl
-variety of flags] that may be combined with the =perl= option when
+variety of flags] that may be combined with the [^perl] option when
constructing the regular expression, in particular note that the
-=newline_alt= option alters the syntax, while the =collate=, =nosubs= and
-=icase= options modify how the case and locale sensitivity are to be applied.
+[^newline_alt] option alters the syntax, while the [^collate], [^nosubs] and
+[^icase] options modify how the case and locale sensitivity are to be applied.
[h3 Pattern Modifiers]
-The perl =smix= modifiers can either be applied using a =(?smix-smix)=
+The perl [^smix] modifiers can either be applied using a [^(?smix-smix)]
prefix to the regular expression, or with one of the
[link boost_regex.ref.syntax_option_type.syntax_option_type_perl regex-compile time
-flags =no_mod_m=, =mod_x=, =mod_s=, and =no_mod_s=].
+flags [^no_mod_m], [^mod_x], [^mod_s], and [^no_mod_s]].
[h3 References]
projects / platform / upstream / boost.git / blobdiff