Question

I have a Perl program, that needs to use packages (that I also write). Some of those packages are only chosen in Runtime (based on some environment variable). I don’t want to put in my code a ‘use’ line for all of those packages, of course, but only one ‘use’ line, based on this variable, something like:

use $ENV{a}; 

Unfortunately, this doesn’t work, of course. Any ideas on how to do this?

Thanks in advance, Oren

Answer 1

eval 'require $ENV{a}'; 

‘use‘ doesn’t work well here because it only imports in the context of the eval.

As @Manni said, actually, it’s better to use require. Quoting from man perlfunc:

 If EXPR is a bareword, the require assumes a '.pm' extension and  replaces '::' with '/' in the filename for you, to make it easy to  load standard modules.  This form of  loading of modules does not  risk altering your namespace.  In other words, if you try this:          require Foo::Bar;    # a splendid bareword  The require function will actually look for the 'Foo/Bar.pm' file  in the directories specified in the @INC array.  But if you try this:          $class = 'Foo::Bar';         require $class;      # $class is not a bareword     #or         require 'Foo::Bar';  # not a bareword because of the ''  The require function will look for the 'Foo::Bar' file in the @INC  array and will complain about not finding 'Foo::Bar' there.  In this  case you can do:          eval 'require $class';