Scripting id3 tags with id3v2 and sed

Question

I am trying to write a script to automatically add track and title info to an mp3 file's id3 tag.

At this point, I have sed grabbing the info from the filename and formatting it to fit the id3v2 command, but upon hitting a multi-word title, I get the error Couldn't stat file '<second word of title>'. If I just echo the id3v2 command that is being run, I see the command in this format:

id3v2 -t Title\ Of\ Track -T 1 1_-_Title_Of_Track.mp3

Copy/pasting that text into the terminal executes tagging properly, but of course lacks the intended automation of scripting. So here's what the script intending to automate the process looks like:

#!/bin/bash

for track in *.mp3 ; do
    id3v2 $(echo ${track} | sed -e 's/^\([1-9][0-9]*\)_-_\(.*\).mp3/-t \2 -T \1/' -e 's/_/\\ /g') ${track}
done

Any insight as to why the title is treated as a single argument when manually typed but not when scripted?

Answer 1

Based on the comments from Valentin B and mueh, I ditched sed for the parsing in the script and instead used bash's string manipulation. While sed was good for parsing multiple data and ordering it in a single command, the command-expansion to use the result would split the output up into "words" that would be delimited by spaces even if the spaces were preceded by backslash or surrounded by quotes.

So instead of trying to construct all of the arguments to id3v2 in a single pass with sed, it was broken up into parsing out the track number and title separately using bash's string manipulation. The end result:

for track in *.mp3 ; do
    track_num=${track%_-_*}
    title=${track#*_} ; title=${title%.mp3} ; title=${title//_/ }
    id3v2 -t "${title}" -T ${track_num} ${track}
done

Thanks to mueh for explaining exactly why my approach in the question was not working, and Valentin B for introducing bash's string manipulation.