#! /usr/bin/perl open (INPUT, "userlog.txt") or die "Couldn't open input file!"; open (OUTPUT, ">userlog.out") or die "Couldn't open output file!"; while ($line = ) { if ($line =~ m/^Password: (.*)/) { $result = `./encryptString $1`; if ($? != 0) { exit(-1) } print OUTPUT "Password: $result\n"; } else { print OUTPUT "$line"; } } close (INPUT); close (OUTPUT);