18.2. Globbing
Bash itself cannot recognize Regular Expressions. Inside scripts, it is commands and utilities — such as sed and awk — that interpret RE’s.
Bash does carry out filename expansion [1] — a process known as globbing — but this does not use the standard RE set. Instead, globbing recognizes and expands wild cards. Globbing interprets the standard wild card characters [2] — * and ?, character lists in square brackets, and certain other special characters (such as ^ for negating the sense of a match). There are important limitations on wild card characters in globbing, however. Strings containing * will not match filenames that start with a dot, as, for example, .bashrc. [3] Likewise, the ? has a different meaning in globbing than as part of an RE.
bash$ ls -l total 2 -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 a.1 -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1 -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1 -rw-rw-r-- 1 bozo bozo 466 Aug 6 17:48 t2.sh -rw-rw-r-- 1 bozo bozo 758 Jul 30 09:02 test1.txt bash$ ls -l t?.sh -rw-rw-r-- 1 bozo bozo 466 Aug 6 17:48 t2.sh bash$ ls -l [ab]* -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 a.1 -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1 bash$ ls -l [a-c]* -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 a.1 -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1 -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1 bash$ ls -l [^ab]* -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1 -rw-rw-r-- 1 bozo bozo 466 Aug 6 17:48 t2.sh -rw-rw-r-- 1 bozo bozo 758 Jul 30 09:02 test1.txt bash$ ls -l {b*,c*,*est*} -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 b.1 -rw-rw-r-- 1 bozo bozo 0 Aug 6 18:42 c.1 -rw-rw-r-- 1 bozo bozo 758 Jul 30 09:02 test1.txt |
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Bash performs filename expansion on unquoted command-line arguments. The echo command demonstrates this.
bash$ echo * a.1 b.1 c.1 t2.sh test1.txt bash$ echo t* t2.sh test1.txt bash$ echo t?.sh t2.sh |
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| It is possible to modify the way Bash interprets special characters in globbing. A set -f command disables globbing, and the nocaseglob and nullglob options to shopt change globbing behavior. |
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See also Example 11-5.
| | Filenames with embedded whitespace can cause globbing to choke. David Wheeler shows how to avoid many such pitfalls. | IFS="$(printf '\n\t')" # Remove space. # Correct glob use: # Always use for-loop, prefix glob, check if exists file. for file in ./* ; do # Use ./* ... NEVER bare * if [ -e "$file" ] ; then # Check whether file exists. COMMAND ... "$file" ... fi done # This example taken from David Wheeler's site, with permission. | | --- | |
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Notes
| [1] | Filename expansion means expanding filename patterns or templates containing special characters. For example, example.??? might expand to example.001 and/or example.txt. |
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| [2] | A wild card character, analogous to a wild card in poker, can represent (almost) any other character. |
| [3] | Filename expansion can match dotfiles, but only if the pattern explicitly includes the dot as a literal character. | ~/[.]bashrc # Will not expand to ~/.bashrc ~/?bashrc # Neither will this. # Wild cards and metacharacters will NOT #+ expand to a dot in globbing. ~/.[b]ashrc # Will expand to ~/.bashrc ~/.ba?hrc # Likewise. ~/.bashr* # Likewise. # Setting the "dotglob" option turns this off. # Thanks, S.C. | | --- | |