#!/usr/bin/perl
# usage: ./script.pl filename search replacement

$^I = '.orig'; # create backup of file at file.orig

my $search = $ARGV[1];
my $replace = $ARGV[2];
my $difference = length $search - length $replace;

@ARGV = ($ARGV[0]);
while (<>) {
    s~s:([0-9]+):"$search([^"]*)~"s:".($1-$difference).":\"$replace$2"~ge;
    print;
}