While working over most of the operating systems today, no program can access a file directly. This is in order to allow the Operaring System to apply user rights. Before you can read from a file you have to ask the Operating System to "open" it for you. When opening a file you provide a variable that will become your handle to the opened file. It is called a filehandle.
#!/usr/bin/perl use strict; use warnings; my $filename = "input.txt"; open(my $fh, "<", $filename); close $fh;