use strict;

open (IN, "<$ARGV[0]") || die "Could not open source file!\n";
my @content = <IN>;
close IN;
open (OUT, ">$ARGV[0]") || die "Could not write to file!\n";
foreach (@content)
{
	if (/^\Q$ARGV[1]/)
	{
		print OUT "$ARGV[2]\n";
	}
	else
	{
		print OUT $_;
	}
}
