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So I'm trying to make a simple script that takes a source dir, and a destination dir as arguments, and creates an identical directory structure at the destination, then converts every file in the source, and puts it in the corresponding destination directory using the GNU parallel command.

My script looks like this:

#!/bin/bash
SOURCE=$1
DEST=$2
find $SOURCE -type f -name '*.flac' -printf "%P\n" | parallel --dry-run mkdir -p $DEST{//}
find $SOURCE -type f -name '*.flac' -printf "%P\n" | parallel --dry-run ffmpeg -loglevel info -i {} -codec:a libmp3lame -qscale:a 3 $DEST{/.}.mp3

Huzzah! The mkdir works as expected (yes, mkdir will try to make a directory for every file, and I'm OK with that, for now).

However, on the ffmpeg line, the output doesn't end up at $DEST. In fact, it appears that the $DEST is null, as it doesn't show up in my --dry-run output.

So as I was writing this, I had a thought, and used this simplified replacement for the ffmpeg line just to play around with it:

find $SOURCE -type f -name '*.flac' -printf "%P\n" | parallel --dry-run echo {} $DEST{/.}.mp3

The same behavior was seen. Cool. Then I moved where $DEST is, like this:

find $SOURCE -type f -name '*.flac' -printf "%P\n" | parallel --dry-run echo {} {$DEST/.}.mp3

And amazingly, moving the $DEST inside the {/.} works! However, trying the same trick in the MKDIR case, like {$DEST//}, doesn't work.

So why does the MKDIR case only work using $DEST{//}, and the simplified case only work using {$DEST/.}?

Thanks!

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So I kept playing with this script, and it felt like I was aiming at a moving target. I wasn't keeping super close track of my changes and what-not, so there may have been other issues going on.

However, I think I've fixed my script to work correctly.

The goal of this script, is to take an arbitrary source directory, that contains *.flac and *.jpg files, create an identical directory structure at the destination, then re-encode all the *.flac files in that source, and write the *.mp3 in the destination directory. Finally, copy all the *.jpg (cover art) in the source directory to the corresponding destination directory. Use GNU parallel as much as possible.

TL;DR - Convert a FLAC directory tree, to an MP3 directory tree, using parallel.

Here's what I finally came up with

#!/bin/sh
SOURCE=$1
DEST=$2
find $SOURCE -type f -name '*.flac' -printf "%h\n" | uniq | parallel --dry-run mkdir -p {=s:$SOURCE:$DEST:g=}
find $SOURCE -type f -name '*.flac' -printf "%P\n" | parallel --dry-run ffmpeg -loglevel info -i $SOURCE{} -codec:a libmp3lame -qscale:a 3 $DEST{.}.mp3
find $SOURCE -type f -name '*.jpg' -printf "%P\n" | parallel --dry-run cp $SOURCE{} $DEST{}

It seems to work, at least for the --dry-run output, as above. Feel free to (re-)use this.

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