Imported from ../bash-4.0-rc1.tar.gz.

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Jari Aalto 2009-01-12 13:36:28 +00:00
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doc/FAQ
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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
@ -79,6 +79,8 @@ E11) If I resize my xterm while another program is running, why doesn't bash
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
@ -908,7 +910,9 @@ D1) Why does bash run a different version of `command' than
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
@ -1425,6 +1429,34 @@ COMP_WORDBREAKS=${COMP_WORDBREAKS//:}
You can also quote the colon with a backslash to achieve the same result
temporarily.
E14) Why does quoting the pattern argument to the regular expression matching
conditional operator (=~) cause regexp matching to stop working?
In versions of bash prior to bash-3.2, the effect of quoting the regular
expression argument to the [[ command's =~ operator was not specified.
The practical effect was that double-quoting the pattern argument required
backslashes to quote special pattern characters, which interfered with the
backslash processing performed by double-quoted word expansion and was
inconsistent with how the == shell pattern matching operator treated
quoted characters.
In bash-3.2, the shell was changed to internally quote characters in single-
and double-quoted string arguments to the =~ operator, which suppresses the
special meaning of the characters special to regular expression processing
(`.', `[', `\', `(', `), `*', `+', `?', `{', `|', `^', and `$') 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'?
@ -1742,7 +1774,12 @@ this:
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?
@ -1791,8 +1828,8 @@ it in fine bookstores near you. This edition of the book has been updated
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.