Re^3: How to get at perl's options in a program

A fairly reliable way to test if a module was loaded is to check for an associated entry in the Symbol Tables:

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

package Foo;
1;

package main;
print "Data::Dumper was ", defined $Data::{'Dumper::'} ? "loaded\n" : 
+"not loaded\n";
print "Foo was ", defined $::{'Foo::'} ? "loaded\n" : "not loaded\n";
print "Eata::Dumper was ", defined $Eata::{'Dumper::'} ? "loaded\n" : 
+"not loaded\n";
[download]

This solution can be applied for any -M or -d. But, to the best of my understanding, the arguments themselves are lost to the ether.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

Comment on Re^3: How to get at perl's options in a program Select or Download Code

Replies are listed 'Best First'.
Re^4: How to get at perl's options in a program by tobyink (Canon) on Nov 06, 2012 at 22:09 UTC
That's actually a pretty flaky technique. use strict; use warnings; use Data::Dumper; package Foo; 1; package main; print "Data::Dumper was ", defined $Data::{'Dumper::'} ? "loaded\n" : +"not loaded\n"; print "Foo was ", defined $::{'Foo::'} ? "loaded\n" : "not loaded\n"; print "Eata::Dumper was ", defined $Eata::{'Dumper::'} ? "loaded\n" : +"not loaded\n"; # Here's a false positive! # "Data::Dumper" was loaded, and that makes it look like # "Data" has also been loaded... # print "Data was ", defined $::{'Data::'} ? "loaded\n" : "not loaded\n" +; # Here's another false positive! # When we checked if "Eata::Dumper" was loaded, # autovivification makes it look like "Eata" was loaded. # print "Eata was ", defined $::{'Eata::'} ? "loaded\n" : "not loaded\n" +; [download] It's much better to check for the existence of the actual functions/methods you wish to use: `my $Dumper = UNIVERSAL::can('Data::Dumper', 'can') && 'Data::Dumper'->can('Dumper'); print $Dumper->($hashref) if defined $Dumper;` [download] `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^4: How to get at perl's options in a program
by tobyink (Canon) on Nov 06, 2012 at 22:09 UTC

That's actually a pretty flaky technique.

use strict;
use warnings;
use Data::Dumper;

package Foo;
1;

package main;
print "Data::Dumper was ", defined $Data::{'Dumper::'} ? "loaded\n" : 
+"not loaded\n";
print "Foo was ", defined $::{'Foo::'} ? "loaded\n" : "not loaded\n";
print "Eata::Dumper was ", defined $Eata::{'Dumper::'} ? "loaded\n" : 
+"not loaded\n";

# Here's a false positive!
# "Data::Dumper" was loaded, and that makes it look like
# "Data" has also been loaded...
#
print "Data was ", defined $::{'Data::'} ? "loaded\n" : "not loaded\n"
+;

# Here's another false positive!
# When we checked if "Eata::Dumper" was loaded, 
# autovivification makes it look like "Eata" was loaded.
#
print "Eata was ", defined $::{'Eata::'} ? "loaded\n" : "not loaded\n"
+;
[download]

It's much better to check for the existence of the actual functions/methods you wish to use:

my $Dumper = UNIVERSAL::can('Data::Dumper', 'can')
             && 'Data::Dumper'->can('Dumper');
print $Dumper->($hashref) if defined $Dumper;
[download]

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

[reply]
[d/l]
[select]