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

CORE(3p) Perl Programmers Reference Guide CORE(3p) #

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

NNAAMMEE #

 CORE - Namespace for Perl's core routines

SSYYNNOOPPSSIISS #

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

DDEESSCCRRIIPPTTIIOONN #

 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"

OOVVEERRRRIIDDIINNGG CCOORREE FFUUNNCCTTIIOONNSS #

 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

AAUUTTHHOORR #

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

SSEEEE AALLSSOO #

 perlsub, perlfunc.

perl v5.36.3 2019-02-13 CORE(3p)