use strict;
open sourcefile, '<', "source.cbl" or die "Can't open: $!";
open targetfile, '>', "source.ada" or die "Can't open: $!";

while (defined (my $line = <sourcefile>)) {
    if ($line =~ s/WORKING -STORAGE SECTION\./declare;/) {
        print targetfile $line;
    } elsif ($line =~ s/PROGRAM -BEGIN\./begin/) {
        print targetfile $line;