my $pattern = q/(...)(...)/;
my $replace = q/$2-$1/;
s/$pattern/$replace/g;
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However, if you trust your invoker, you could try something like:

my $pattern = q/(...)(...)/;
my $replace = q/$2-$1/;
s/$pattern/qq{$replace}/eeg;
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-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

Thank you for your help. I think I'm still having a problem with the line:

s/$pattern/qq{$replace}/eeg;

Here's the snippet that's failing:


# get strings from GUI.  
my $old = my $new = $_->children->get; # get old filename
my $pattern = $form->{'entry2'}->get_text();
# e.g. $pattern == "^(\d{2})\. (.*)$" after this
my $replace = $form->{'entry1'}->get_text();
# e.g. $replace == "two-$2, one-$1" after this

# is the following match necessary? $1, etc
# need to be assigned somehow...
if($old =~ /$pattern/) {
    $new =~ s/$pattern/qq{$replace}/eeg;
    print STDERR $old." => ".$new."\n";
}
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After the $new =~ line, $new is empty, every time. Am I missing something? Thanks again

$new = $old;
$new =~ s/$pattern/qq{$replace}/eeg;
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But you're scaring me here. I said that the string had to be from a trusted source. As soon as you start talking "GUI", that makes me think that the user-ID of the person typing the string is not necessarily the user-ID of the person running the code.

Let me reemphasize. Using this code as-is will allow any arbitrary Perl code to be executed, including shelling out to execute arbitrary system commands. Clear? It's not just about mangling a string. You must either trust the invoker, or not use this code.

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

There's no easy way to do this save for parsing the replace-with string yourself. There's a rename script which comes with Perl, that allows you to pass Perl code as the first parameter, which it then executes for every file, passing the filename in $_ and moving the file if the code modified $_.

Note that $1 et al are most likely subject to parsing by the shell on Unixoid systems, as are parens and the backslash, so if you want to use them, you'll need to enclose the parameters in single quotes to prevent those characters from being interpreted by the shell.

Probably the sanest solution would be to use a printfish syntax for the right side, composing a new string from the captured bits for every match. Something like this (untested; esp. the pattern).

my ($re, $fmt) = @ARGV;

function reformat {
    local $_ = $fmt;
    s/%(?:(\d+)|.)/$_[$1] if defined $1/ge;
    return $_;
}

# ...

$re = qr/$re/; # precompile

for(@list_of_files) {
    next unless (my @capture = /$re/);
    rename $_, reformat(@capture);
}
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Makeshifts last the longest.