-This is the Bash FAQ, version 3.34, for Bash version 3.2.
+This is the Bash FAQ, version 3.36, for Bash version 3.2.
This document contains a set of frequently-asked questions concerning
Bash, the GNU Bourne-Again Shell. Bash is a freely-available command
notice the change?
E12) Why don't negative offsets in substring expansion work like I expect?
E13) Why does filename completion misbehave if a colon appears in the filename?
+E14) Why does quoting the pattern argument to the regular expression matching
+ conditional operator (=~) cause matching to stop working?
Section F: Things to watch out for on certain Unix versions
On many systems, `which' is actually a csh script that assumes
you're running csh. In tcsh, `which' and its cousin `where'
are builtins. On other Unix systems, `which' is a perl script
-that uses the PATH environment variable.
+that uses the PATH environment variable. Many Linux distributions
+use GNU `which', which is a C program that can understand shell
+aliases.
The csh script version reads the csh startup files from your
home directory and uses those to determine which `command' will
You can also quote the colon with a backslash to achieve the same result
temporarily.
+E14) Why does quoting the pattern argument to the regular expression matching
+ conditional operator (=~) cause regexp matching to stop working?
+
+In versions of bash prior to bash-3.2, the effect of quoting the regular
+expression argument to the [[ command's =~ operator was not specified.
+The practical effect was that double-quoting the pattern argument required
+backslashes to quote special pattern characters, which interfered with the
+backslash processing performed by double-quoted word expansion and was
+inconsistent with how the == shell pattern matching operator treated
+quoted characters.
+
+In bash-3.2, the shell was changed to internally quote characters in single-
+and double-quoted string arguments to the =~ operator, which suppresses the
+special meaning of the characters special to regular expression processing
+(`.', `[', `\', `(', `), `*', `+', `?', `{', `|', `^', and `$') and forces
+them to be matched literally. This is consistent with how the `==' pattern
+matching operator treats quoted portions of its pattern argument.
+
+Since the treatment of quoted string arguments was changed, several issues
+have arisen, chief among them the problem of white space in pattern arguments
+and the differing treatment of quoted strings between bash-3.1 and bash-3.2.
+Both problems may be solved by using a shell variable to hold the pattern.
+Since word splitting is not performed when expanding shell variables in all
+operands of the [[ command, this allows users to quote patterns as they wish
+when assigning the variable, then expand the values to a single string that
+may contain whitespace. The first problem may be solved by using backslashes
+or any other quoting mechanism to escape the white space in the patterns.
+
Section F: Things to watch out for on certain Unix versions
F1) Why can't I use command line editing in my `cmdtool'?
echo .!(.|) *
A solution that works without extended globbing is given in the Unix Shell
-FAQ, posted periodically to comp.unix.shell.
+FAQ, posted periodically to comp.unix.shell. It's a variant of
+
+ echo .[!.]* ..?* *
+
+(The ..?* catches files with names of three or more characters beginning
+with `..')
Section H: Where do I go from here?
to cover bash-3.0.
The GNU Bash Reference Manual has been published as a printed book by
-Network Theory Ltd (Paperback, ISBN: 0-9541617-7-7, Feb 2003). It covers
-bash-2.0 and is available from most online bookstores (see
+Network Theory Ltd (Paperback, ISBN: 0-9541617-7-7, Nov. 2006). It covers
+bash-3.2 and is available from most online bookstores (see
http://www.network-theory.co.uk/bash/manual/ for details). The publisher
will donate $1 to the Free Software Foundation for each copy sold.
projects / platform / upstream / bash.git / blobdiff