[SOLVED] Technique - alternatives to tell if directory empty or not

grail · 07-13-2011, 08:17 PM

So this is just a query on personal preferences about what method you would use in a bash script to tell if a directory contained any (this needs to include hidden) files or directories?
The current method I am using is:

Code:

anyford=$(ls -A | wc -l)
if (( anyford > 0 ))
then
    <do stuff here>
fi

I am normally abhorred to use ls if I can help it so would appreciate any feedback on what others would use in this scenario?

Cheers
grail

Sergei Steshenko · 07-13-2011, 09:00 PM

Quote:

Originally Posted by grail

So this is just a query on personal preferences about what method you would use in a bash script to tell if a directory contained any (this needs to include hidden) files or directories?
The current method I am using is:

Code:

anyford=$(ls -A | wc -l)
if (( anyford > 0 ))
then
    <do stuff here>
fi

I am normally abhorred to use ls if I can help it so would appreciate any feedback on what others would use in this scenario?

Cheers
grail

Maybe 'stat', specifically, "Links: 2":

Code:

sergei@amdam2:~/junk> /usr/bin/stat .
  File: `.'
  Size: 233472          Blocks: 464        IO Block: 4096   directory
Device: 803h/2051d      Inode: 5325145     Links: 78
Access: (0755/drwxr-xr-x)  Uid: ( 1000/  sergei)   Gid: (  100/   users)
Access: 2011-07-14 04:53:22.000000000 +0300
Modify: 2011-07-14 04:52:40.000000000 +0300
Change: 2011-07-14 04:52:40.000000000 +0300
sergei@amdam2:~/junk> cd empty_dir/
sergei@amdam2:~/junk/empty_dir> /usr/bin/stat .
  File: `.'
  Size: 4096            Blocks: 8          IO Block: 4096   directory
Device: 803h/2051d      Inode: 5382458     Links: 2
Access: (0755/drwxr-xr-x)  Uid: ( 1000/  sergei)   Gid: (  100/   users)
Access: 2011-07-14 04:52:43.000000000 +0300
Modify: 2011-07-14 04:52:40.000000000 +0300
Change: 2011-07-14 04:52:40.000000000 +0300
sergei@amdam2:~/junk/empty_dir> ls -ltrA
total 0
sergei@amdam2:~/junk/empty_dir>

?

Though I've never studied internals of Linux file systems and can't tell whether "Links: 2" is correct/portable.

ta0kira · 07-13-2011, 09:16 PM

Quote:

Originally Posted by Sergei Steshenko

Though I've never studied internals of Linux file systems and can't tell whether "Links: 2" is correct/portable.

Each directory contains 2 hard-linked directories: . and .. (I'm not sure if this is technically true for the base of a filesystem, but at least the kernel pretends it's that way). If a directory has 2 links that only means it has no subdirectories; it could still have files.

ls might be the way to go, except it will fail if your user has --x access and not r-x. Then again, why would you need to know that if you had --x?
Kevin Barry

grail · 07-13-2011, 09:40 PM

I have reviewed options for stat and confirmed ta0kira's information is correct that Links: only refers to the number of
directories (or hard links) within a directory, when used in this manner, so not appropriate for my current task.

Thanks for the feedback though

Sergei Steshenko · 07-13-2011, 09:51 PM

Quote:

Originally Posted by grail

I have reviewed options for stat and confirmed ta0kira's information is correct that Links: only refers to the number of
directories (or hard links) within a directory, when used in this manner, so not appropriate for my current task.

Thanks for the feedback though

Then you have "Blocks: 8" too.

ta0kira · 07-13-2011, 10:10 PM

Quote:

Originally Posted by Sergei Steshenko

Then you have "Blocks: 8" too.

This will stay the same up to a certain limit of number of contained files. It also might differ with filesystem type.
Kevin Barry

grail · 07-13-2011, 10:10 PM

hmmm ... now I think you are stretching. I ran stat on an empty directory and one with files in it and the Blocks count
is the same ... so no real value to that measurement

ntubski · 07-13-2011, 10:13 PM

Code:

shopt -s dotglob nullglob
dir_or_files=(*)
if ((${#dir_or_files[@]} > 0))

Unfortunately it requires specific globbing options.

ntubski · 07-27-2011, 07:04 AM

find can also identify empty directories:

Code:

find . -type d -empty

grail · 07-27-2011, 10:59 AM

Thanks for the new idea

I would probably have to add maxdepth as well as only interested i current directory.

the idea I am trying to use it for is when a user removes an application I need to test a directory that may need to be removed as other applications
may also have installed files in the directory and hence it should not be removed so as to not break the other applications.

ta0kira · 07-27-2011, 01:36 PM

Quote:

Originally Posted by grail

Thanks for the new idea

I would probably have to add maxdepth as well as only interested i current directory.

the idea I am trying to use it for is when a user removes an application I need to test a directory that may need to be removed as other applications
may also have installed files in the directory and hence it should not be removed so as to not break the other applications.

Maybe you just need to rmdir /path || true.
Kevin Barry

grail · 07-27-2011, 02:23 PM

Thanks for the suggestion Kevin. May I ask what purpose the '|| true' serves here? It does not seem to alleviate any error messages (which of course I can through to /dev/null).

ta0kira · 07-27-2011, 03:22 PM

Quote:

Originally Posted by grail

Thanks for the suggestion Kevin. May I ask what purpose the '|| true' serves here? It does not seem to alleviate any error messages (which of course I can through to /dev/null).

Just a habbit from writing makefiles and controlling the return value of shell functions, I suppose.
Kevin Barry

gnashley · 07-27-2011, 03:31 PM

Here's a pure-shell version:

Code:

set $(echo .* *)
[ $3 ] # non-empty or maybe you'd like `[ -n $3 ]` better

colucix · 07-27-2011, 03:58 PM

Another bash approach:

Code:

[ dir/* == "dir/*" ] 2> /dev/null && echo empty

This is true only if the directory is empty, otherwise you get an error. Single square brackets are mandatory, since filename expansion doesn't take place inside double square brackets.