I've found the following script very useful for this task. This is the 'rename' script from Programming Perl, 1st Edition, updated a bit for perl5.

#!/usr/local/bin/perl

# Usage: rename <perlexpr> [files]

($op = shift) || die "Usage: $0 <perlexpr> [files]\n";

chomp(@ARGV = <STDIN>) unless @ARGV;

for (@ARGV) {
    $was = $_;
    eval $op;
    die $@ if $@;
    rename($was,$_) unless $was eq $_;
}
[download]

The book also includes some examples of using the script.

Rename files matching *.bak to strip the extension:   rename 's/\.bak$//' *.abc Add the extensions back on:

  rename '$_ .= ".bak"' *

  rename 's/$/.bak/' *
[download]

Translate uppercase names to lower:   rename 'tr/A-Z/a-z/' * And more:

  rename 's/foo/bar; $_ = $was if -e' *foo*

  find . -print | rename 's/readme/README/i'

  find . -print | rename 's/$/.old/ if -M $_ > 0.5'

  find . -name '*,v' -print | \
    rename 's#(.*)/#$1/RCS#, $x{$1}++ || mkdir("$1/RCS", 0777)'
[download]

It was sad that the later editions of Programming Perl didn't include the sample scripts, but fortunately the Perl CookBook has since filled that need.