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По какой-то причине мой find -foo не был на должном уровне, поэтому я взломал один ответ stackexchange на замену find и придумал это.

#!/bin/bash
# mytime is the number of seconds of the mp3 that you want to delete,
# in this case 3 minutes
mytime=180
files="$(find -L "<put your top level directory here>" -type f -name  "*.mp3")";
# are there any files at all?
if [[ "$files" == "" ]]; then
    echo "No files";
    return 0;
fi
echo "$files" | while read file; do 
    # take the file, find the time, convert to seconds
    times="$(mp3info -p "%m:%s\n" "$file" |awk -F':' '{print ($1*60)+$2}')"
    # if that is greater than 3*60, we delete the file, which is $file.
    if [[ "$times" -lt "mytime" ]]
    then
        # WARNING, there be dragons here... 
        echo "We are removing $file from the system..."
        rm "$file"
    fi 
done