Handle names with spaces when iterating recursively over files

Question

I am trying to recursively convert all .mkv files in a folder structure with subfolders to .mp4.

I got a standard line that works in just the present folder

for video in *.mkv; do ffmpeg -i "$video" -acodec aac -ac 2 "${video%.*}".mp4; rm "$video"; done

So I thought I would make something like

for video in $(find . -name *.mp4); do ffmpeg -i "$video" -acodec aac -ac 2 "${video%.*}".mkv; rm "$video"; done

But this seems to fail on folders with spaces in them. Can anyone point out my error?

Check out BashFAQ #20: "How can I find and safely handle file names containing newlines, spaces or both?" Note that ffmpeg consumes its input, so you need to work around that (see BashFAQ #89: "I'm reading a file line by line and running ssh or ffmpeg, only the first line gets processed!"). — Gordon Davisson, Apr 29 '22 at 19:15

Kusalananda · Accepted Answer · 2022-04-29T19:59:21.200

Your error lies in using find in a command substitution. A command substitution always results in a single string. If you leave the substitution unquoted, that string will undergo splitting on spaces, tabs and newlines (by default). The split-up words will be processed for filename globbing. The resulting strings are what your loop will iterate over, which is not what you want.

Your loop that works for the current directory (fixing the issue with filenames starting with a dash):

for video in ./*.mkv; do
    ffmpeg -i "$video" -acodec aac -ac 2 "${video%.*}".mp4
    rm "$video"
done

Changed to work recursively, by enabling the ** globbing pattern (and using nullglob to avoid running the loop at all if there are no matches):

shopt -s globstar nullglob
for video in ./*/.mkv; do
    ffmpeg -i "$video" -acodec aac -ac 2 "${video%.*}".mp4
    rm "$video"
done

The two loops above would not care about the filetype and would happily feed ffmpeg with symbolic links, directories, or any other non-regular type of file, as long as the name matched the given pattern.

Alternatively, delegating the recursive generation of pathnames to find (also only selecting regular files):

find . -name '*.mkv' -type f -exec sh -c '
    for video do
        ffmpeg -i "$video" -acodec aac -ac 2 "${video%.*}".mp4
        rm "$video"
    done' sh {} +

The above would also find hidden names matching the pattern, which the first two shell loops would not do (unless you enable the dotglob shell option).

Handle names with spaces when iterating recursively over files

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