Making a bash script apply to only selected files (Nautilus)

Question

I'm trying to learn (with no programming background) to create some custom bash scripts for converting selected files from Nautilus, but I hit an issue I can't understand.

For reference, this is a script that DOES work. It converts selected .MP4 files to .mkv, copies the time stamp and prints some feedback to the user.

#!/bin/bash

for i in $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS
do 
    ffmpeg -i "$i" -movflags use_metadata_tags -c:v libx265 -crf 26 -preset slow -c:a aac -b:a 160k "${i%.*}.mkv" && touch -r "$i" "${i%.*}.mkv" && notify-send "Converted '$(basename "$i")'" || notify-send "Failed converting '$(basename "$i")'"
done

notify-send "Conversion finished"

Now, this is a script that DOESN'T work. It should convert selected .m4a files to .mp3, add a cover image and some tags, copy the time stamp and give some feedback to the user.

#!/bin/bash

for i in $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS
do 
    ffmpeg -i "$i" "${i%.*}.mp3" && eyeD3 -a "Author" -A "Album" --add-image="cover.jpg":FRONT_COVER "${i%.*}.mp3" && touch -r "$i" "${i%.*}.mp3" && notify-send "Converted '$(basename "$i")'" || notify-send "Failed converting '$(basename "$i")'"
done

notify-send "Conversion finished"

When I run this one, I get multiple errors that say "Failed converting (a part of the path to the file)"... for some parts of the path to the file, like parts of folder and file names.

I'm not sure what I'm doing differently here. I'm using the same $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS parameter, but it doesn't work the same in the second script.

As a reference, this other script, which is the same as the second one but applies to all the files in the folder, does work perfectly, so I'm sure the commands inside do do work.

#!/bin/bash

for i in *.m4a
do 
    ffmpeg -i "$i" "${i%.*}.mp3" && eyeD3 -a "Author" -A "Album" --add-image="cover.jpg":FRONT_COVER "${i%.*}.mp3" && touch -r "$i" "${i%.*}.mp3" && notify-send "Converted '$(basename "$i")'" || notify-send "Failed converting '$(basename "$i")'"
done

notify-send "Conversion finished"

What am I missing? Can the $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS only work with certain file types? Is the issue somewhere else?

Answer 1

This is how I would rewrite the failing script. I cannot test it but the concern I have is that there's no clarity regarding the directory in which the script runs. Does cover.jpg really exist?

It would be worth adding a notify-send "$PWD" near the top to check that the script is running from the expected directory. If it's not, then perhaps the relevant directory can be inferred from the value being processed from $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS (you might need to change "cover.jpg" to "${src%/*}/cover.jpg").

#!/bin/bash
count=0 success=0

# Transform command line arguments (if provided)
[[ -z "$NAUTILUS_SCRIPT_SELECTED_FILE_PATHS" ]] &&
    NAUTILUS_SCRIPT_SELECTED_FILE_PATHS=$(printf "%s\n" "$@")

# Process each file in turn
while IFS= read -r src
do
    # Target
    dst="${i%.*}.mp3"

    # Primary conversion to mp3
    step=0
    ffmpeg -i "$src" "$dst" && ((step++))

    # Add album cover (if available)
    if [[ step -eq 1 ]]
    then
        if [[ -f "cover.jpg" ]]
        then
            eyeD3 -a "Author" -A "Album" --add-image="cover.jpg":FRONT_COVER "$dst" && ((step++))
        else
            ((step++))
        fi
    fi

    # Reset the timestamp
    if [[ step -eq 2 ]]
    then
        touch -r "$src" "$dst" && ((step++))
    fi

    # Notify the user
    if [[ step -eq 3 ]]
    then
        notify-send "Converted '${src##*/}'"
        ((success++))
    else
        notify-send "Failed converting '${src##*/}' at step $step"
    fi

    # Count it
    ((count++))

done <<<"$NAUTILUS_SCRIPT_SELECTED_FILE_PATHS"

[[ count -gt 1 ]] &&
    notify-send "Conversion finished ($success files of $count)"

exit $((count - success))

You could probably protect the notify-send calls with something like [[ -n "$DISPLAY" ]] && notify-send … but I can't be totally sure. This would then allow you to run the script from batch (at, for example) with command-line arguments.