What does assigning ‘shift‘ to a variable mean?

原文链接：https://stackoverflow.com/questions/7082811/what-does-assigning-shift-to-a-variable-mean/7082897

Example:

use strict;
my $file = shift;

open(IN, $file) || die "Unable to open $file\n";
open(OUT, ">$file.$$") or die $!;

You can read the documentation on shift. It is very clear. shift accepts an array and extracts the first element (actually removing it from the array). If you don’t provide any array, it uses @ARGV (the arguments to the command line of the program) to read the data. If you’re inside a function, it uses @_, namely, the parameters of the function.