diff options
author | Jari Aalto <jari.aalto@cante.net> | 2009-01-12 13:36:28 +0000 |
---|---|---|
committer | Jari Aalto <jari.aalto@cante.net> | 2009-09-12 16:47:00 +0000 |
commit | 3185942a5234e26ab13fa02f9c51d340cec514f8 (patch) | |
tree | 2c6fcd01779faef1f91c5d84d63981ca3479137d /doc/FAQ | |
parent | f1be666c7d78939ad775078d290bec2758fa29a2 (diff) | |
download | android_external_bash-3185942a5234e26ab13fa02f9c51d340cec514f8.tar.gz android_external_bash-3185942a5234e26ab13fa02f9c51d340cec514f8.tar.bz2 android_external_bash-3185942a5234e26ab13fa02f9c51d340cec514f8.zip |
Imported from ../bash-4.0-rc1.tar.gz.
Diffstat (limited to 'doc/FAQ')
-rw-r--r-- | doc/FAQ | 47 |
1 files changed, 42 insertions, 5 deletions
@@ -1,4 +1,4 @@ -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. |