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", "each", "eof", "exec",
"exists", "keys", "lstat", "pop",
"push", "shift", "splice", "split",
"stat", "system", "truncate",
"unlink", "unshift", "values"
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.