Requires the Errno module. Each element of %! has a nonzero value only if $! is set to that value.

Contains the current environment. The key is the name of an environment variable; the value is its current setting.

Defines names for sets of symbols. Used by the Exporter module.

Contains the list of files that have been included with use, require, or do. The key is the filename as specified with the command; the value is the location of the file.

Registers signal handlers for various signals. The key is the name of the signal (without the SIG prefix); the value a subroutine that is executed when the signal occurs.

__WARN__ and __DIE__ are pseudo-signals to attach handlers to Perl warnings and exceptions.