How can I use two bash commands in -exec of find command? WITH GREP

Question

I would like to do the same as How can I use two bash commands in -exec of find command? but with grep as the second command. The solutions posted for that prior solution don't work when grep is the second command. Another question Combination of find and grep command with exec option inquires about using grep, but all the answers don't use grep. I think I need grep.

For example,

sudo find -D exec . -maxdepth 1 -type f -iname "*" -exec file -N '{}' \; -exec echo 'asdf' \;

works fine, but

sudo find -D exec . -maxdepth 1 -type f -iname "*" -exec file -N '{}' \; -exec grep "JPEG" {} \;

shows no evidence of grep doing anything. How can I force the stdout of the first command to stdin for grep? If I instead, pipe the file command output to a file and run grep separately on the file it works great:

dell@DELL-E6440:~$ rm junk.txt
dell@DELL-E6440:~$ sudo find -D exec . -maxdepth 1 -type f -iname "*" -exec file -N '{}' >> junk.txt \;
dell@DELL-E6440:~$ grep "JPEG" junk.txt
./150120-ssc-proxy~20190508-061623.jpg: JPEG image data, JFIF standard 1.01, resolution (DPI), density 150x150, segment length 16, baseline, precision 8, 1018x1426, frames 3
./avoid-powered-overfight~20190508-061623.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, comment: "Intel(R) JPEG Library, version [2.0.16.48]", baseline, precision 8, 1048x659, frames 3
dell@DELL-E6440:~$

but the point is I want to do it on one bash line, and >> doesn't properly flush the file between runs anyhow.

Answer 1

If you want to run file on every file and then grep the output from file for the string JPEG:

find . -maxdepth 1 -type f -exec file {} + | grep JPEG

This runs file on batches of regular files, producing a stream of result output. This stream is then filtered by grep for lines containing the particular string JPEG. Note that filenames containing newlines would be misrepresented in the output of this pipeline.

Your command in the question would run grep on the files themselves, not on the output of the file command. Your find command also uses -iname "*" which is a no-op since all filenames matches that predicate.

Alternatively, using bash to loop over the files in the current directory:

shopt -s dotglob nullglob

for name in ./*; do
    mimetype=$( file --brief --mime-type "$name" )
    if [[ $mimetype == */jpeg ]]; then
        printf '"%s" is a JPEG file\n' "$name"
    fi
done

This would use the MIME-type reported for each file in the current directory by file to filter out the names that correspond to JPEG files.

A slightly expanded example:

shopt -s dotglob nullglob

for name in ./*; do
    mimetype=$( file --brief --mime-type "$name" )
    case $mimetype in
        */jpeg)   printf '"%s" is a JPEG file\n'             "$name" ;;
        */png)    printf '"%s" is a PNG file\n'              "$name" ;;
        image/*)  printf '"%s" is some form of image file\n' "$name" ;;
        *)        printf '"%s" is not an image file\n'       "$name"
    esac
done

And finally, using the MIME-type directly in find:

find . -maxdepth 1 -exec bash -c '[[ $(file -b --mime-type "$1") == */jpeg ]]' bash {} \; -print

or, more efficiently,

find . -maxdepth 1 -exec bash -c '
    for pathname do
        [[ $(file -b --mime-type "$pathname") == */jpeg ]] && printf "%s\n" "$pathname"
    done' bash {} +

These last two commands will just print out the pathnames corresponding to JPEG images.

Answer 2

Wrapping two commands into the find command wasn't the best idea. Instead, I unwrapped the two operations from within find and instead sequenced them through pipes.

$ sudo find . -type f | file -Nz -f - | grep -f ~/badtypes.txt

This now gives me a way of recursing with the file command, and find any types of file that do not belong on the computer, regardless of whether they've been renamed or compressed. I wonder why the file command doesn't naturally have a recurse option.

Answer 3

Kusa's ...-exec file {} + | grep ...

Your find | file -f - | grep

And also this:

]# cat fhs.sh 
#/bin/bash
file -Nz * | grep "magic"

]# find . -exec ./fhs.sh {} +
uout: very short file (no magic)

All seem to work, using the same amount of time. Some other variations also work, but they take longer.

---

Normally, the find ... -exec grep xxx {} + construct is very efficient (the + instead of \;). But here, with file, you "interfere" with the filenames.

So here, your "flat" (pipeline) approach is OK.