From perldoc -f require:

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
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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 ""
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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";
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...

Having been bitten by this in some code that needs to require the module based on a run time value (solved the problem with an eval), I wonder what the underlying reasons are for not applying the same rules for a scalar string as for a bareword.

Is it

• a hangover from earlier Perl versions, before 'use' became widespread?
• something that is actually needed in some circumstances (i.e. not translating Foo::Bar to Foo/Bar)?
• some other reason I haven't thought of?

How much code would break if this were made consistent? (not much as far as I can think of)

I also notice that use similarly insists on a bareword.

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