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Mastering Modern Perl: Writing Efficient and Maintainable Code

Pragmas

Learn about pragmas, how they behave in scopes, and how to use them.

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Most Perl modules provide new functions or define classes. Others, such as strict or warnings, influence the behavior of the language itself. This second type of module is a pragma. By convention, pragma names are written in lowercase to differentiate them from other modules.

Pragmas and scope

Pragmas work by exporting specific behavior or information into the lexical scopes of their callers.

We’ve seen how declaring a lexical variable makes a symbol name available within a scope. Using a pragma makes its behavior effective within a scope as well:

Perl
{
    # $lexical not visible; strict not in effect
    {
        use strict;
        my $lexical = 'available here';
        # $lexical is visible; strict is in effect
    }
    # $lexical again invisible; strict not in effect
}

Just as lexical declarations affect inner scopes, pragmas maintain their effects within inner scopes:

Perl
# file scope
use strict;
{
  # inner scope, but strict still in effect
  my $inner = 'another lexical';
}

Using pragmas

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