What does “1;” mean in Perl?

Question

I have come across a few Perl modules that for example look similar to the following code:

package MyPackage;

use strict;
use warnings;
use constant PERL510         


        

Answer 1

Perl modules must return something that evaluates to true. If they don't, Perl reports an error.

C:\temp>cat MyTest.pm
package MyTest;
use strict;
sub test { print "test\n"; }
#1;  # commented out to show error

C:\temp>perl -e "use MyTest"
MyTest.pm did not return a true value at -e line 1.
BEGIN failed--compilation aborted at -e line 1.

C:\temp>

Although it's customary to use "1;", anything that evaluates to true will work.

C:\temp>cat MyTest.pm
package MyTest;
use strict;
sub test { print "test\n"; }
"false";

C:\temp>perl -e "use MyTest"

C:\temp>  (no error here)

For obvious reasons another popular return value is 42.

There's a list of cool return values maintained at http://returnvalues.useperl.at/values.html.