BASH: Filter list of files by return value of another command - linux

Question

I have series of directories with (mostly) video files in them, say
test1
1.mpg
2.avi
3.mpeg
junk.sh
test2
123.avi
432.avi
432.srt
test3
asdf.mpg
qwerty.mpeg
I create a variable (video_dir) with the directory names (based on other parameters) and use that with find to generate the basic list. I then filter based on another variable (video_type) for file types (because there is sometimes non-video files in the dirs) piping it through egrep. Then I shuffle the list around and save it out to a file. That file is later used by mplayer to slideshow through the list.
I currently use the following command to accomplish that. I'm sure it's a horrible way to do it, but it works for me and it's quite fast even on big directories.
video_dir="/test1 /test2"
video_types=".mpg$|.avi$|.mpeg$"
find ${video_dir} -type f |
egrep -i "${video_types}" |
shuf > "$TEMP_OUT"
I now would like to add the ability to filter out files based on the resolution height of the video file. I can get that from.
mediainfo --Output='Video;%Height%' filename
Which just returns a number. I have tried using the -exec functionality of find to run that command on each file.
find ${video_dir} -type f -exec mediainfo --Output='Video;%Height%' {} \;
but that just returns the list of heights, not the filenames and I can't figure out how to reject ones based on a comparison, like <480.
I could do a for next loop but that seems like a bad (slow) idea.
Using info from #mark-setchell I modified it to,
video_dir="test1"
find ${video_dir} -type f \
-exec bash -c 'h=$(mediainfo --Output="Video;%Height%" "$1"); [[ $h -gt 480 ]]' _ {} \; -print
Which works.

Answer 1

You can replace your egrep with the following so you are still inside the find command (-iname is case insensitive and -o represents a logical OR):
find test1 test2 -type f \
\( -iname "*.mpg" -o -iname "*.avi" -o -iname "*.mpeg" \) \
NEXT_BIT
The NEXT_BIT can then -exec bash and exit with status 0 or 1 depending on whether you want the current file included or excluded. So it will look like this:
-exec bash -c 'H=$(mediainfo -output ... "$1"); [ $H -lt 480 ] && exit 1; exit 0' _ {} \;
So, taking note of #tripleee advice in comments about superfluous exit statements, I get this:
find test1 test2 -type f \
\( -iname "*.mpg" -o -iname "*.avi" -o -iname "*.mpeg" \) \
-exec bash -c 'h=$(mediainfo ...options... "$1"); [ $h -lt 480 ]' _ {} \; -print

Answer 2

This Q&A was focused on one particular case, so the accepted answer is not as general as it could be.
find
If the list of files comes from find, one can use its filtering facilities, e.g. -exec:
find ${video_dir} -type f \
-exec COMMAND \; \
-print
Here
COMMAND is not enclosed in quotes -- find reads everything after -exec and up to a \;
find will expand {} to the current file name (including path -- you might find -execdir helpful, which will cd to the file's directory and replace {} with the leaf file name)
The exit code of COMMAND is treated as follows:
0 -> true
non-0 -> false
Note that you can build more complex expressions (e.g. -not -exec ...), which will be evaluated "from left to right, according to the rules of precedence ... -and is assumed where the operator is omitted." (per man find)
xargs
If the list of files comes from elsewhere (and is available on stdin), you can use xargs as follows (from
If xargs is map, what is filter? )
ls | xargs -I{} bash -c "COMMAND '{}' && echo '{}'"

Answer 3

Here is my solution.
#!/bin/bash
shopt -s nullglob
video_dir=(/test1 /test2)
while IFS= read -rd '' file; do
if [[ $file = *.#(mpg|avi|mpeg|mp4) ]]; then
h=$(mediainfo --Output="Video;%Height%" "$file")
(( h >= 480 )) && echo "$file"
fi
done < <(find "${video_dir[#]}" -type f -print0)
This solution you can process everything inside the while read loop.