Re^4: Prepending to a file

[afoken]

or die "Could not open file ", $file, ": $!";

Looks good. It seems you found a bug.

Because filenames may contain spaces and other "invisible" characters, especially when the code generating the filename has a bug (e.g missing chomp), you may want to quote it in the error message. And you could use string interpolation for the filename. So:

 or die "Could not open file '$file': $!";

Alexander