Your description but that not work it is not so useful to me to understand what you want to achieve.

Constructs like unless (A && B) are potentially confusing: your call to error_info happens only if GetOptions returns true and also $show_help is defined. It does not seems too logical to me.

After I read The Dynamic Duo --or-- Holy Getopt::Long, Pod::UsageMan! i usually start with something like:

use Getopt::Long;
use Pod::Usage;

unless ( GetOptions (
                        "color=s"=>\$par_color,
                        "help"     => \$par_help,
                     )
        ) {pod2usage(-verbose => 1)}

if (defined $par_help){pod2usage(-verbose => 1)}
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pod2usage implicitly exit the program. And is a sane behaviour: exit if arguments are not what you expected and exit if user requested help to be shown.

After this you need to manually validate your given arguments, but this is another story..

See also GetOpt Organization

HtH

L*

Sorry, I means, if GetOptions can get the right options and find the --help option ，it should show the help info output by error_info(), or if GetOptions failed to get the right options, some errors happend, it also should show the help info. but when I execute the script likes below:

my.pl --help
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there's no output, so why?

When I run your code:

use Getopt::Long;

my ( $timeout, $show_help ) = 30;
unless ( GetOptions("timeout|t=i" => \$timeout, "help|h|?" => \$show_h
+elp) && $show_help ) {
    error_info();
}
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I get the following output:

Undefined subroutine &main::error_info called at tmp.pl line 5. </c>

This is what I expect. If I call your script with --help like this:

perl -w tmp.pl --help
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I get no output. This is also what I expect, because your && expression is not true ($show_help and GetOptions will be true, which never satisfies an unless statement).

Maybe you want to use less clever code like the approach outlined in the documentation of Getopt::Long?

use Getopt::Long;

GetOptions(
    "timeout|t=i" => \my $timeout,
    "help|h|?" => \my $show_help
) or die "bad options.";

$timeout ||= 30;

if ( $show_help ) {
    print "Showing help\n";
    error_info();
}
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but that not work, why?

it not work "because"

also I've never found the return value of GetOptions to be reliable for any use, ignore it