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. Likewise, the ? has a different
meaning in globbing than as part of an RE.
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.
Examples of globbing
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
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
Note: 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.
See also TODO Example 11-5.
Caution: Filenames with embedded whitespace can cause globbing to choke.
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.