Here is the code in question in context; it is part of Getopt::Long

use Getopt::Long qw( :config bundling noignorecase passthrough );
GetOptions (
    "help|?"    => sub { usage 0; },
    "V|version" => sub { print "$cmd [$VERSION]\n"; exit 0; },
    "man"       => sub { exec "pod2man $0 | nroff -man"; },
    "info"      => sub { require Pod::Usage;
                         Pod::Usage::pod2usage (VERBOSE => 2);
                         exit;
                         },
 
    "o|c|out=s" => \my $csv,
    "i|s|in=s"  => \my $xls,
    "f|force!"  => \my $opt_f,
 
    "A|all!"    => \my $opt_a,
    "N|no-pfx!" => \my $opt_N,
    ) or usage 1;
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It is assigning the value from the -o, -c, or --out switches to the $csv lexical variable that it is defining in-line