The warnings pragma is a replacement for the command line flag -w, but the pragma is limited to the enclosing block, while the flag is global. See perllexwarn for more information.

If no import list is supplied, all possible warnings are either enabled or disabled.

A number of functions are provided to assist module authors.

use warnings::register

Creates a new warnings category with the same name as the package where the call to the pragma is used.

warnings::enabled()

Use the warnings category with the same name as the current package.

Return TRUE if that warnings category is enabled in the calling module. Otherwise returns FALSE.

warnings::enabled($category)

Return TRUE if the warnings category, $category, is enabled in the calling module. Otherwise returns FALSE.

warnings::enabled($object)

Use the name of the class for the object reference, $object, as the warnings category.

Return TRUE if that warnings category is enabled in the first scope where the object is used. Otherwise returns FALSE.

warnings::warn($message)

Print $message to STDERR.

Use the warnings category with the same name as the current package.

If that warnings category has been set to ``FATAL'' in the calling module then die. Otherwise return.

warnings::warn($category, $message)

Print $message to STDERR.

If the warnings category, $category, has been set to ``FATAL'' in the calling module then die. Otherwise return.

warnings::warn($object, $message)

Print $message to STDERR.

Use the name of the class for the object reference, $object, as the warnings category.

If that warnings category has been set to ``FATAL'' in the scope where $object is first used then die. Otherwise return.

warnings::warnif($message)

Equivalent to:

    if (warnings::enabled())
      { warnings::warn($message) }

warnings::warnif($category, $message)

Equivalent to:

    if (warnings::enabled($category))
      { warnings::warn($category, $message) }

warnings::warnif($object, $message)

Equivalent to:

    if (warnings::enabled($object))
      { warnings::warn($object, $message) }