CORE(3)

CORE(3perl)            Perl Programmers Reference Guide            CORE(3perl)

NAME
       CORE - Namespace for Perl's core routines

SYNOPSIS
           BEGIN {
               *CORE::GLOBAL::hex = sub { 1; };
           }

           print hex("0x50"),"\n";                     # prints 1
           print CORE::hex("0x50"),"\n";               # prints 80
           CORE::say "yes";                            # prints yes

           BEGIN { *shove = \&CORE::push; }
           shove @array, 1,2,3;                        # pushes on to @array

DESCRIPTION
       The "CORE" namespace gives access to the original built-in functions of
       Perl.  The "CORE" package is built into Perl, and therefore you do not
       need to use or require a hypothetical "CORE" module prior to accessing
       routines in this namespace.

       A list of the built-in functions in Perl can be found in perlfunc.

       For all Perl keywords, a "CORE::" prefix will force the built-in
       function to be used, even if it has been overridden or would normally
       require the feature pragma.  Despite appearances, this has nothing to
       do with the CORE package, but is part of Perl's syntax.

       For many Perl functions, the CORE package contains real subroutines.
       This feature is new in Perl 5.16.  You can take references to these and
       make aliases.  However, some can only be called as barewords; i.e., you
       cannot use ampersand syntax (&foo) or call them through references.
       See the "shove" example above.  These subroutines exist for all
       keywords except the following:

       "__DATA__", "__END__", "and", "cmp", "default", "do", "dump", "else",
       "elsif", "eq", "eval", "for", "foreach", "format", "ge", "given",
       "goto", "grep", "gt", "if", "last", "le", "local", "lt", "m", "map",
       "my", "ne", "next", "no", "or", "our", "package", "print", "printf",
       "q", "qq", "qr", "qw", "qx", "redo", "require", "return", "s", "say",
       "sort", "state", "sub", "tr", "unless", "until", "use", "when",
       "while", "x", "xor", "y"

       Calling with ampersand syntax and through references does not work for
       the following functions, as they have special syntax that cannot always
       be translated into a simple list (e.g., "eof" vs "eof()"):

       "chdir", "chomp", "chop", "defined", "delete", "eof", "exec", "exists",
       "lstat", "split", "stat", "system", "truncate", "unlink"

OVERRIDING CORE FUNCTIONS
       To override a Perl built-in routine with your own version, you need to
       import it at compile-time.  This can be conveniently achieved with the
       "subs" pragma.  This will affect only the package in which you've
       imported the said subroutine:

           use subs 'chdir';
           sub chdir { ... }
           chdir $somewhere;

       To override a built-in globally (that is, in all namespaces), you need
       to import your function into the "CORE::GLOBAL" pseudo-namespace at
       compile time:

           BEGIN {
               *CORE::GLOBAL::hex = sub {
                   # ... your code here
               };
           }

       The new routine will be called whenever a built-in function is called
       without a qualifying package:

           print hex("0x50"),"\n";                     # prints 1

       In both cases, if you want access to the original, unaltered routine,
       use the "CORE::" prefix:

           print CORE::hex("0x50"),"\n";               # prints 80

AUTHOR
       This documentation provided by Tels <nospam-abuse@bloodgate.com> 2007.

SEE ALSO
       perlsub, perlfunc.

perl v5.30.3                      2020-06-07                       CORE(3perl)