Question

I have Perl code which relies on Term::ReadKey to get the terminal width. My installation is missing this module, so I want to provide a default if the module isn’t present rather than throw an exception.

How can I conditionally use an optional module, without knowing ahead of time whether it is available.

# but only if the module is installed and exists use Term::ReadKey; ... 

How can I accomplish this?

Answer 1

Here’s a bare-bones solution that does not require another module:

my $rc = eval {   require Term::ReadKey;   Term::ReadKey->import();   1; };  if($rc) {   # Term::ReadKey loaded and imported successfully   ... } 

Note that all the answers below (I hope they’re below this one! 🙂 that use eval { use SomeModule } are wrong because use statements are evaluated at compile time, regardless of where in the code they appear. So if SomeModule is not available, the script will die immediately upon compiling.

(A string eval of a use statement will also work (eval 'use SomeModule';), but there’s no sense parsing and compiling new code at runtime when the require/import pair does the same thing, and is syntax-checked at compile time to boot.)

Finally, note that my use of eval { ... } and $@ here is succinct for the purpose of this example. In real code, you should use something like Try::Tiny, or at least be aware of the issues it addresses.