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Update CORE.pod to reflect the new coresubs
[perl5.git] / lib / CORE.pod
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1=head1 NAME
2
4aaa4757 3CORE - Namespace for Perl's core routines
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4
5=head1 SYNOPSIS
6
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7 BEGIN {
8 *CORE::GLOBAL::hex = sub { 1; };
9 }
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11 print hex("0x50"),"\n"; # prints 1
12 print CORE::hex("0x50"),"\n"; # prints 80
4a904372 13 CORE::say "yes"; # prints yes
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15 BEGIN { *shove = \&CORE::push; }
16 shove @array, 1,2,3; # pushes on to @array
17
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18=head1 DESCRIPTION
19
1694bc13 20The C<CORE> namespace gives access to the original built-in functions of
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21Perl. The C<CORE> package is built into
22Perl, and therefore you do not need to use or
5840c18f 23require a hypothetical "CORE" module prior to accessing routines in this
1694bc13 24namespace.
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1694bc13 26A list of the built-in functions in Perl can be found in L<perlfunc>.
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28For all Perl keywords, a C<CORE::> prefix will force the built-in function
29to be used, even if it has been overridden or would normally require the
30L<feature> pragma. Despite appearances, this has nothing to do with the
31CORE package, but is part of Perl's syntax.
32
33For many Perl functions, the CORE package contains real subroutines. This
34feature is new in Perl 5.16. You can take references to these and make
2702a50a 35aliases. However, some can only be called as barewords; i.e., you cannot
4aaa4757 36use ampersand syntax (C<&foo>) or call them through references. See the
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37C<shove> example above. These subroutines exist for all keywords except the following:
38
39C<__DATA__>, C<__END__>, C<and>, C<cmp>, C<default>, C<do>, C<dump>,
40C<else>, C<elsif>, C<eq>, C<eval>, C<for>, C<foreach>, C<format>, C<ge>,
41C<given>, C<goto>, C<grep>, C<gt>, C<if>, C<last>, C<le>, C<local>, C<lt>,
42C<m>, C<map>, C<my>, C<ne>, C<next>, C<no>, C<or>, C<our>, C<package>,
43C<print>, C<printf>, C<q>, C<qq>, C<qr>, C<qw>, C<qx>, C<redo>, C<require>,
44C<return>, C<s>, C<say>, C<sort>, C<state>, C<sub>, C<tr>, C<unless>,
45C<until>, C<use>, C<when>, C<while>, C<x>, C<xor>, C<y>
46
47Calling with
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48ampersand syntax and through references does not work for the following
49functions, as they have special syntax that cannot always be translated
50into a simple list (e.g., C<eof> vs C<eof()>):
51
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52C<chdir>, C<chomp>, C<chop>, C<defined>, C<delete>, C<each>,
53C<eof>, C<exec>, C<exists>, C<keys>, C<lstat>, C<pop>, C<push>,
54C<shift>, C<splice>, C<split>, C<stat>, C<system>, C<truncate>,
2702a50a 55C<unlink>, C<unshift>, C<values>
4aaa4757 56
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57=head1 OVERRIDING CORE FUNCTIONS
58
1694bc13 59To override a Perl built-in routine with your own version, you need to
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60import it at compile-time. This can be conveniently achieved with the
61C<subs> pragma. This will affect only the package in which you've imported
1694bc13 62the said subroutine:
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64 use subs 'chdir';
65 sub chdir { ... }
66 chdir $somewhere;
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68To override a built-in globally (that is, in all namespaces), you need to
69import your function into the C<CORE::GLOBAL> pseudo-namespace at compile
70time:
71
72 BEGIN {
73 *CORE::GLOBAL::hex = sub {
74 # ... your code here
75 };
76 }
77
78The new routine will be called whenever a built-in function is called
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79without a qualifying package:
80
1694bc13 81 print hex("0x50"),"\n"; # prints 1
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83In both cases, if you want access to the original, unaltered routine, use
84the C<CORE::> prefix:
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1694bc13 86 print CORE::hex("0x50"),"\n"; # prints 80
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87
88=head1 AUTHOR
89
1694bc13 90This documentation provided by Tels <nospam-abuse@bloodgate.com> 2007.
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91
92=head1 SEE ALSO
93
1694bc13 94L<perlsub>, L<perlfunc>.
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95
96=cut