#!/usr/local/bin/perl -w
use strict;
use warnings;
print "Enter the output file you would like to analyze: ";
chomp (my $filename = <STDIN>);
print "Enter the isotope you want to extract (ex: Am-241): ";
chomp (my $iso= <STDIN>);

open(IN, "<", $filename) or die("Can't read the source:$!");

open(OUT, ">Comp_$filename");
select (OUT);

$/ = '0AVERAGE COMPOSITION IN PINS.';

while (<IN>) {
    next if ! /$iso/;
    
    chomp;
    print "$/$_";
}