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

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

     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 Example 11-4.

      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.

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.
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.