for (1..25) {
    warn "File Exists: $_.txt\n" and next if -f "$_.txt";
    print 'My prompt message: ';
    chomp(my $input = <STDIN>);
    open my $fh, '>', "$_.txt"     or warn $! and next;
    open my $ph, '-|', $cmd, $input or warn $! and next;
    {
        local $_;
        while {<$ph>) {
            do_your_processing($_);
            print $fh $_ or die $!;
        }
    }
}