CORE(3pm) Perl Programmers Reference Guide CORE(3pm)
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(1), perlfunc(1).
perl v5.26.1 2017-07-18 CORE(3pm)
perl 5.26.1 - Generated Sat Nov 4 06:24:10 CDT 2017