I think this might be something along the lines of what you want ...

use strict;
use File::Copy;

my $dest_file = "email.lst";
my $searchstr = 'blue';
my $repstr    = 'foo';

open(FL, $dest_file) or die("Doh - $!");

# turn on inplace edit flag (see. man perlvar)
$^I = '~';
s/$searchstr/$repstr/g while <FL>;

close(FL);

move($dest_file, $repstr);
[download]

This just opens a file, does a search and replace within the file (see. the $^I variable), then renames it to the new file. This could probably be done in a line or two of shell and perl, but this is nice'n'pure :o)
HTH

broquaint