Trying to do arithmetic in Perl rename tool (Debian)

Question

Supposed I have five mp3 files:

01-trackfoo.mp3
02-trackbar.mp3
03-trackbaz.mp3
04-trackabc.mp3
05-trackxyz.mp3

Now I give a quick listen to the files (just mplayer on console will do the trick) and I find out that the order is wrong. 05 is actually 02 and the rest will have to be renamed. So first I will do a temp rename:

01-trackfoo.mp3

02-trackbar.mp3
03-trackbaz.mp3
04-trackabc.mp3
00-trackxyz.mp3

Now we need a "shift": 02 should become 03, 03 should become 04 and 04 should become 05. To minimize confusion, ex-05 (now 00) will just be mved later.

My approach was this: (perl rename, by Larry Wall, default here on Debian)

rename 's/0([2-4])([\s\S]+)/0($1+1)$2/' *

as well as (later, after some more RTFM'ing)

rename 's/0([2-4])([\s\S]+)/0($1+1)$2/e' *

None of them worked, especially because the /e[val] modifier does not accept anything else but evaluations, and will throw an error once you attempt to combine the evaluations with strings. Bash can do it just fine, e. g. foo$((1+6)) will be evaluated to foo7.

So how can I do this (one-liner preferred, not intending to write a whole standalone script just for this)?

Answer 1

You almost had it. You just need to make literal strings and string concatenation explicit within the /e-modified substitution, using quotes and the dot operator.

rename 's/0([2-4])([\s\S]+)/"0".($1+1).$2/e' *

Answer 2

one-liner preferred, not intending to write a whole standalone script just for this

When things get so complicated, I don't see any reason not to write a script. You're never going to remember how to do this from one run to the next, so you're going to end up either reinventing it each time, or wrapping it up in a script anyway.

For a small thing like this, I generally start trying to solve it in Bash:

#!/bin/bash
if [ -z "$1" ] ; then echo Need arguments. ; exit 1 ; fi

typeset -i i=1
for f in "$*"
do
    tailbits=`echo "$f" | sed -e 's/^[0-9]+//'`
    mv "$f" sertmp-`printf %02d $i`"$tailbits"
    i=i+1
done

for f in "sertmp-*"
do
    mv "$f" `echo "$f" | sed -e s/^sertmp-//` 
done

Basically, this script strips off any leading digits, then puts a zero-padded increasing serial number on the front, with the files numbered according to the order you pass them to the script.

It does this in two stages, with sertmp- prefixes for the first pass to avoid any risk of name collisions. If you call this script mp3-renamer and call it like:

$ mp3-renamer 01-foo.mp3 03-bar.mp3 04-qux.mp3

you run into a trivial collision on the first rename if you don't use 2 passes to do the renaming. (01-foo.mp3 -> 01-foo.mp3.)

If you call it like this, though:

$ mp3-renamer 02-foo.mp3 01-foo.mp3

you accidentally erase 01-foo.mp3 in the first rename with a 1-pass rename.

If the problem gets more complicated, I'd rewrite it in Perl. At that point, you could then use a hash to hold the old->new name mapping, and use a bit of clever code to work out the proper order to do the renamings in order to avoid the need for 2 passes.