If you want the user to type the file name into the interactive terminal that Padre spawns, then you should assign the file name from STDIN - see I/O Operators in perlop. That code will probably look like:
in reply to Re^4: user input file
in thread user input file
The chomp is necessary because your input will have a trailing newline which is not in the file name.
my $filename = <>;
open(FILE,"<", $filename) or die "Open failed for $filename: $!";
#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.