I assume this is the entire body of the script, and not just a snippet. I also assume you are running perl with the -i switch. If you simply modify that to be perl -i.bak ..., your issue will be solved. See perlrun.

If you have your -i switch in your hashbang, just modify it there instead.

Update: If all you are doing is appending "\n##Copyright (C) 2012 by firstName lastName\n" to the tail of the file, why are you using switches when you could just open the file for appending, and append? e.g.

use File::Copy;

for my $file (@ARGV) {
    -e $file or warn("File not found: $file\n"), next;
    
    copy($file, "$file.bak") or die "Copy failed ($file): $!";
    open my $fh, '>>', $file or die "Open failed ($file): $!";
    print $fh "\n##Copyright (C) 2012 by firstName lastName\n";
}
[download]

I'm not that advanced, I just started playing with perl a couple weeks ago so I'm still learning how it works.

I would argue that's exactly why you should adopt this approach. As a new user, you should avoid using classic Perl "magic", and make sure your code is straight-forward and readable. The script, as I've presented it, loops over the passed file names (@ARGV), tests to make sure you've passed file names that can be found (-e), copies the files using a CORE module (File::Copy) and then modifies the file with an append (perlopentut). It tests if operations succeed and is warnings and strict compliant. I never use command line switches in any of my code unless I'm writing one-liners, and half that time it would have been faster just to write a proper script.

---

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

#! /usr/bin/perl -i.bak

Nevermind, it was in the wrong format. Should be this:

#! /usr/bin/perl -i[.bak]
[download]

but now it still doesn't make a copy, or at least I don't see it in my directory.

I added that to the top and now at the command line, I run the file...

~$ fileName textfile.txt

it returns this:

Unrecognized switch: -.bak (-h will show valid options).

I checked out the valid options and -i should work but for some reasons it isnt.

I tried this but it doesn't work. It clears the original file and prints the copywrite line to the command line. Seems that it has to do with the way <> works with the -i option. See my node below.

From How can I use Perl's i option from within a program? the -i option changes $^I which in turn changes how <> works. That means the magic only works inside a while loop that uses <>. Your code with -i added on for me made a .bak copy but cleared the original and printed to the command line. The following code does what you requested.

#!/perl -i.bak

while(<>) {
    print;
    if(eof) {
        print "\n";
        print "##Copyright (C) 2012 by firstName lastName\n" ;
    }
}
[download]

Script works great thanks a lot! Is it possible to have the backup get modified instead of the original? Only the original gets the modification. Thanks again.

You could use kennethk's updated solution but open the newly created backup in append mode instead of the original.