Thanks for pointing this out! Much of my code uses =s, and I now realize I have bugs. However, upon closer inspection of Getopt::Long, it is documented:

       = type [ desttype ] [ repeat ]
           The option requires an argument of the given type. Supporte
+d types are:

           s   String. An arbitrary sequence of characters. It is vali
+d for the argument
               to start with "-" or "--".
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Note that it is much less likely (or impossible?) to happen with =i or =f.

For those who store options in a hash, Athanasius' handler approach doesn't apply directly. Here is an equivalent:

use warnings;
use strict;
use Getopt::Long qw(GetOptions);

my %opt;
GetOptions(\%opt, qw(name=s long)) or die;
if ( (exists $opt{name}) and ($opt{name} =~ /^-/) ) {
    die "Option name requires an argument\n";
}
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or, more generally...

my %opt;
my @string_opts = qw(name foo|goo bar);
GetOptions(\%opt, qw(help long), map { "$_=s" } @string_opts) or die;

for my $oname (@string_opts) {
    $oname = (split /\|/, $oname)[0]; # handle alternate names
    if ( (exists $opt{$oname}) and ($opt{$oname} =~ /^-/) ) {
        die "Option $oname requires an argument\n";
    }
}
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