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| == How can I check whether a directory is empty or not? == ''I just deleted three completely '''wrong''' answers from this question. Please, people, make sure that when you add to the FAQ, your answers'' * answer the question that was asked, and * actually '''work''' ''Thanks. -- GreyCat'' |
== How can I check whether a directory is empty or not? How do I check for any *.mpg files? == |
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| Most modern systems have an "ls -A" which explicitly omits "." and ".." from the directory listing: | In Bash, you can do this safely and easily with the nullglob and dotglob options (which change the behaviour of [:glob:globbing]), and arrays: |
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| if [ -n "$(ls -A somedir)" ] then echo directory is non-empty fi |
# Bash shopt -s nullglob dotglob files=(*) (( ${#files[*]} )) || echo directory is empty shopt -u nullglob dotglob |
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| This can be shortened to: | As you can see we unset the nullglob after using it, to prevent it affecting other globs in the script in unexpected ways. `nullglob` also simplifies various other operations: |
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| if [ "$(ls -A somedir)" ] then echo directory is non-empty fi }}} Another way, using Bash features, involves setting the special shell option which changes the behavior of globbing. Some people prefer to avoid this approach, because it's so drastically different and could severely alter the behavior of scripts. Nevertheless, if you're willing to use this approach, it does greatly simplify this particular task: {{{ shopt -s nullglob if [[ -z $(echo *) ]]; then echo directory is empty fi }}} It also simplifies various other operations: {{{ |
# Bash |
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| shopt -u nullglob | |
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| Without the {{{shopt}}}, that would have to be: | Without the {{{nullglob}}}, that would have to be: |
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| # Bash | |
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| Finally, you may wish to avoid the ''direct'' question altogether. Usually people want to know whether a directory is empty... ''because'' they want to do something involving the files therein, etc. Look to the larger question. For example, something like this may be an appropriate solution: | In fact, you may wish to avoid the ''direct'' question altogether. Usually people want to know whether a directory is empty... ''because'' they want to do something involving the files therein, etc. Look to the larger question. For example, one of these [:UsingFind:find-based examples] may be an appropriate solution: |
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| # Bourne | |
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| find "$somedir" -maxdepth 0 -empty -exec echo {} is empty. \; # GNU/BSD find "$somedir" -type d -empty -exec cp /my/configfile {} \; # GNU/BSD |
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| It's all a matter of addressing the program's actual requirements. | If your script needs to run with various shell implementations, you can try using an external program like python, perl, or find as indicated above, or you can try something like: {{{ # Bourne # (Of course, the system must have printf(1).) cd foo || exit 1 if test "$(printf '%s %s %s' .* *)" = '. .. *' && ! test -f '*' then echo "directory is empty" fi }}} Yes, it's extremely ugly, but it should be more portable than anything depending on `ls` output. Even `ls -A` solutions can break (HPUX for one, if you are root). |
How can I check whether a directory is empty or not? How do I check for any *.mpg files?
In Bash, you can do this safely and easily with the nullglob and dotglob options (which change the behaviour of [:glob:globbing]), and arrays:
# Bash
shopt -s nullglob dotglob
files=(*)
(( ${#files[*]} )) || echo directory is empty
shopt -u nullglob dotglobAs you can see we unset the nullglob after using it, to prevent it affecting other globs in the script in unexpected ways. nullglob also simplifies various other operations:
# Bash
shopt -s nullglob
for i in *.zip; do
blah blah "$i" # No need to check $i is a file.
done
shopt -u nullglobWithout the nullglob, that would have to be:
# Bash
for i in *.zip; do
[[ -f $i ]] || continue # If no .zip files, i becomes *.zip
blah blah "$i"
done(You may want to use the latter anyway, if there's a possibility that the glob may match directories in addition to files.)
In fact, you may wish to avoid the direct question altogether. Usually people want to know whether a directory is empty... because they want to do something involving the files therein, etc. Look to the larger question. For example, one of these [:UsingFind:find-based examples] may be an appropriate solution:
# Bourne
find "$somedir" -type f -exec echo Found unexpected file {} \;
find "$somedir" -maxdepth 0 -empty -exec echo {} is empty. \; # GNU/BSD
find "$somedir" -type d -empty -exec cp /my/configfile {} \; # GNU/BSDIf your script needs to run with various shell implementations, you can try using an external program like python, perl, or find as indicated above, or you can try something like:
# Bourne
# (Of course, the system must have printf(1).)
cd foo || exit 1
if test "$(printf '%s %s %s' .* *)" = '. .. *' && ! test -f '*'
then
echo "directory is empty"
fiYes, it's extremely ugly, but it should be more portable than anything depending on ls output. Even ls -A solutions can break (HPUX for one, if you are root).