How can I take a reference to a Perl subroutine? - perl

Question

I'm having some trouble figuring out how to make a reference to a subroutine in an external module file. Right now, I'm doing this:
External file
package settingsGeneral;
sub printScreen {
print $_[0];
}
Main
use settingsGeneral;
my $printScreen = settingsGeneral::printScreen;
&$printScreen("test");
but this result into an error:
Can't use string ("1") as a subroutine ref while "strict refs" in use

Answer 1

As noted in perlmodlib, you should start your module's name with an uppercase letter:
Perl informally reserves lowercase module names for 'pragma' modules like integer and strict. Other modules normally begin with a capital letter and use mixed case with no underscores (need to be short and portable).
One way to call a sub defined in another package is to fully qualify that sub's name when you call it:
SettingsGeneral::printScreen "important message\n";
If all you want is a reference to printScreen, grab it with the backslash operator
my $subref = \&SettingsGeneral::printScreen;
and call it with one of
&$subref("one\n");
&{$subref}("two\n");
$subref->("three\n");
You could create an alias in your current package:
*printScreen = \&SettingsGeneral::printScreen;
printScreen("another urgent flash\n");
Skip the parentheses (necessary because the sub in the current package wasn't known at compile time) by writing:
use subs 'printScreen';
*printScreen = \&SettingsGeneral::printScreen;
printScreen "the sky is falling!\n";
The Exporter module can do this custodial work for you:
SettingsGeneral.pm:
package SettingsGeneral;
use Exporter 'import';
our #EXPORT = qw/ printScreen /;
sub printScreen {
print $_[0];
}
1;
main:
#! /usr/bin/perl
use warnings;
use strict;
use SettingsGeneral;
printScreen "foo!\n";