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.\" ========================================================================
.\"
.IX Title "CORE 3perl"
.TH CORE 3perl "2023-11-25" "perl v5.36.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
CORE \- Namespace for Perl's core routines
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&    BEGIN {
\&        *CORE::GLOBAL::hex = sub { 1; };
\&    }
\&
\&    print hex("0x50"),"\en";                     # prints 1
\&    print CORE::hex("0x50"),"\en";               # prints 80
\&    CORE::say "yes";                            # prints yes
\&
\&    BEGIN { *shove = \e&CORE::push; }
\&    shove @array, 1,2,3;                        # pushes on to @array
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`CORE\*(C'\fR namespace gives access to the original built-in functions of
Perl.  The \f(CW\*(C`CORE\*(C'\fR package is built into
Perl, and therefore you do not need to use or
require a hypothetical \*(L"\s-1CORE\*(R"\s0 module prior to accessing routines in this
namespace.
.PP
A list of the built-in functions in Perl can be found in perlfunc.
.PP
For all Perl keywords, a \f(CW\*(C`CORE::\*(C'\fR 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
\&\s-1CORE\s0 package, but is part of Perl's syntax.
.PP
For many Perl functions, the \s-1CORE\s0 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 (\f(CW&foo\fR) or call them through references.  See the
\&\f(CW\*(C`shove\*(C'\fR example above.  These subroutines exist for all keywords except the following:
.PP
\&\f(CW\*(C`_\|_DATA_\|_\*(C'\fR, \f(CW\*(C`_\|_END_\|_\*(C'\fR, \f(CW\*(C`and\*(C'\fR, \f(CW\*(C`cmp\*(C'\fR, \f(CW\*(C`default\*(C'\fR, \f(CW\*(C`do\*(C'\fR, \f(CW\*(C`dump\*(C'\fR,
\&\f(CW\*(C`else\*(C'\fR, \f(CW\*(C`elsif\*(C'\fR, \f(CW\*(C`eq\*(C'\fR, \f(CW\*(C`eval\*(C'\fR, \f(CW\*(C`for\*(C'\fR, \f(CW\*(C`foreach\*(C'\fR, \f(CW\*(C`format\*(C'\fR, \f(CW\*(C`ge\*(C'\fR,
\&\f(CW\*(C`given\*(C'\fR, \f(CW\*(C`goto\*(C'\fR, \f(CW\*(C`grep\*(C'\fR, \f(CW\*(C`gt\*(C'\fR, \f(CW\*(C`if\*(C'\fR, \f(CW\*(C`last\*(C'\fR, \f(CW\*(C`le\*(C'\fR, \f(CW\*(C`local\*(C'\fR, \f(CW\*(C`lt\*(C'\fR,
\&\f(CW\*(C`m\*(C'\fR, \f(CW\*(C`map\*(C'\fR, \f(CW\*(C`my\*(C'\fR, \f(CW\*(C`ne\*(C'\fR, \f(CW\*(C`next\*(C'\fR, \f(CW\*(C`no\*(C'\fR, \f(CW\*(C`or\*(C'\fR, \f(CW\*(C`our\*(C'\fR, \f(CW\*(C`package\*(C'\fR,
\&\f(CW\*(C`print\*(C'\fR, \f(CW\*(C`printf\*(C'\fR, \f(CW\*(C`q\*(C'\fR, \f(CW\*(C`qq\*(C'\fR, \f(CW\*(C`qr\*(C'\fR, \f(CW\*(C`qw\*(C'\fR, \f(CW\*(C`qx\*(C'\fR, \f(CW\*(C`redo\*(C'\fR, \f(CW\*(C`require\*(C'\fR,
\&\f(CW\*(C`return\*(C'\fR, \f(CW\*(C`s\*(C'\fR, \f(CW\*(C`say\*(C'\fR, \f(CW\*(C`sort\*(C'\fR, \f(CW\*(C`state\*(C'\fR, \f(CW\*(C`sub\*(C'\fR, \f(CW\*(C`tr\*(C'\fR, \f(CW\*(C`unless\*(C'\fR,
\&\f(CW\*(C`until\*(C'\fR, \f(CW\*(C`use\*(C'\fR, \f(CW\*(C`when\*(C'\fR, \f(CW\*(C`while\*(C'\fR, \f(CW\*(C`x\*(C'\fR, \f(CW\*(C`xor\*(C'\fR, \f(CW\*(C`y\*(C'\fR
.PP
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., \f(CW\*(C`eof\*(C'\fR vs \f(CW\*(C`eof()\*(C'\fR):
.PP
\&\f(CW\*(C`chdir\*(C'\fR, \f(CW\*(C`chomp\*(C'\fR, \f(CW\*(C`chop\*(C'\fR, \f(CW\*(C`defined\*(C'\fR, \f(CW\*(C`delete\*(C'\fR, \f(CW\*(C`eof\*(C'\fR, \f(CW\*(C`exec\*(C'\fR,
\&\f(CW\*(C`exists\*(C'\fR, \f(CW\*(C`lstat\*(C'\fR, \f(CW\*(C`split\*(C'\fR, \f(CW\*(C`stat\*(C'\fR, \f(CW\*(C`system\*(C'\fR, \f(CW\*(C`truncate\*(C'\fR, \f(CW\*(C`unlink\*(C'\fR
.SH "OVERRIDING CORE FUNCTIONS"
.IX Header "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
\&\f(CW\*(C`subs\*(C'\fR pragma.  This will affect only the package in which you've imported
the said subroutine:
.PP
.Vb 3
\&    use subs \*(Aqchdir\*(Aq;
\&    sub chdir { ... }
\&    chdir $somewhere;
.Ve
.PP
To override a built-in globally (that is, in all namespaces), you need to
import your function into the \f(CW\*(C`CORE::GLOBAL\*(C'\fR pseudo-namespace at compile
time:
.PP
.Vb 5
\&    BEGIN {
\&        *CORE::GLOBAL::hex = sub {
\&            # ... your code here
\&        };
\&    }
.Ve
.PP
The new routine will be called whenever a built-in function is called
without a qualifying package:
.PP
.Vb 1
\&    print hex("0x50"),"\en";                     # prints 1
.Ve
.PP
In both cases, if you want access to the original, unaltered routine, use
the \f(CW\*(C`CORE::\*(C'\fR prefix:
.PP
.Vb 1
\&    print CORE::hex("0x50"),"\en";               # prints 80
.Ve
.SH "AUTHOR"
.IX Header "AUTHOR"
This documentation provided by Tels <nospam\-abuse@bloodgate.com> 2007.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perlsub, perlfunc.