Test whether a glob has any matches in Bash
If I want to check for the existence of a single file, I can test for it using test -e filename
or [ -e filename ]
.
Supposing I have a glob and I want to know whether any files exist whose names match the glob. The glob can match 0 files (in which case I need to do nothing), or it can match 1 or more files (in which case I need to do something). How can I test whether a glob has any matches? (I don't care how many matches there are, and it would be best if I could do this with one if
statement and no loops (simply because I find that most readable).
(test -e glob*
fails if the glob matches more than one file.)
Bash-specific solution:
compgen -G "<glob-pattern>"
Escape the pattern or it'll get pre-expanded into matches.
Exit status is:
- 1 for no-match,
- 0 for 'one or more matches'
stdout
is a list of files matching the glob.
I think this is the best option in terms of conciseness and minimizing potential side effects.
Example:
if compgen -G "/tmp/someFiles*" > /dev/null; then
echo "Some files exist."
fi
The nullglob shell option is indeed a bashism.
To avoid the need for a tedious save and restore of the nullglob state, I'd only set it inside the subshell that expands the glob:
if test -n "$(shopt -s nullglob; echo glob*)"
then
echo found
else
echo not found
fi
For better portability and more flexible globbing, use find:
if test -n "$(find . -maxdepth 1 -name 'glob*' -print -quit)"
then
echo found
else
echo not found
fi
Explicit -print -quit actions are used for find instead of the default implicit -print action so that find will quit as soon as it finds the first file matching the search criteria. Where lots of files match, this should run much faster than echo glob*
or ls glob*
and it also avoids the possibility of overstuffing the expanded command line (some shells have a 4K length limit).
If find feels like overkill and the number of files likely to match is small, use stat:
if stat -t glob* >/dev/null 2>&1
then
echo found
else
echo not found
fi
#!/usr/bin/env bash
# If it is set, then an unmatched glob is swept away entirely --
# replaced with a set of zero words --
# instead of remaining in place as a single word.
shopt -s nullglob
M=(*px)
if [ "${#M[*]}" -ge 1 ]; then
echo "${#M[*]} matches."
else
echo "No such files."
fi
I like
exists() {
[ -e "$1" ]
}
if exists glob*; then
echo found
else
echo not found
fi
This is both readable and efficient (unless there are a huge number of files).
The main drawback is that it's much more subtle than it looks, and I sometimes feel compelled to add a long comment.
If there's a match, "glob*"
is expanded by the shell and all the matches are passed to exists()
, which checks the first one and ignores the rest.
If there's no match, "glob*"
is passed to exists()
and found not to exist there either.
Edit: there may be a false positive, see comment
If you have globfail set you can use this crazy (which you really should not)
shopt -s failglob # exit if * does not match
( : * ) && echo 0 || echo 1
or
q=( * ) && echo 0 || echo 1