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)