1package Symbol; 2 3=head1 NAME 4 5Symbol - manipulate Perl symbols and their names 6 7=head1 SYNOPSIS 8 9 use Symbol; 10 11 $sym = gensym; 12 open($sym, "filename"); 13 $_ = <$sym>; 14 # etc. 15 16 ungensym $sym; # no effect 17 18 # replace *FOO{IO} handle but not $FOO, %FOO, etc. 19 *FOO = geniosym; 20 21 print qualify("x"), "\n"; # "Test::x" 22 print qualify("x", "FOO"), "\n" # "FOO::x" 23 print qualify("BAR::x"), "\n"; # "BAR::x" 24 print qualify("BAR::x", "FOO"), "\n"; # "BAR::x" 25 print qualify("STDOUT", "FOO"), "\n"; # "main::STDOUT" (global) 26 print qualify(\*x), "\n"; # returns \*x 27 print qualify(\*x, "FOO"), "\n"; # returns \*x 28 29 use strict refs; 30 print { qualify_to_ref $fh } "foo!\n"; 31 $ref = qualify_to_ref $name, $pkg; 32 33 use Symbol qw(delete_package); 34 delete_package('Foo::Bar'); 35 print "deleted\n" unless exists $Foo::{'Bar::'}; 36 37=head1 DESCRIPTION 38 39C<Symbol::gensym> creates an anonymous glob and returns a reference 40to it. Such a glob reference can be used as a file or directory 41handle. 42 43For backward compatibility with older implementations that didn't 44support anonymous globs, C<Symbol::ungensym> is also provided. 45But it doesn't do anything. 46 47C<Symbol::geniosym> creates an anonymous IO handle. This can be 48assigned into an existing glob without affecting the non-IO portions 49of the glob. 50 51C<Symbol::qualify> turns unqualified symbol names into qualified 52variable names (e.g. "myvar" -E<gt> "MyPackage::myvar"). If it is given a 53second parameter, C<qualify> uses it as the default package; 54otherwise, it uses the package of its caller. Regardless, global 55variable names (e.g. "STDOUT", "ENV", "SIG") are always qualified with 56"main::". 57 58Qualification applies only to symbol names (strings). References are 59left unchanged under the assumption that they are glob references, 60which are qualified by their nature. 61 62C<Symbol::qualify_to_ref> is just like C<Symbol::qualify> except that it 63returns a glob ref rather than a symbol name, so you can use the result 64even if C<use strict 'refs'> is in effect. 65 66C<Symbol::delete_package> wipes out a whole package namespace. Note 67this routine is not exported by default--you may want to import it 68explicitly. 69 70=head1 BUGS 71 72C<Symbol::delete_package> is a bit too powerful. It undefines every symbol 73that lives in the specified package and in its sub-packages. Since perl, 74for performance reasons, does not perform a symbol table lookup each time 75a function is called or a global variable is accessed, some code that has 76already been loaded and that makes use of symbols in package C<Foo> may 77stop working after you delete C<Foo>, even if you reload the C<Foo> module 78afterwards. 79 80=cut 81 82BEGIN { require 5.005; } 83 84require Exporter; 85@ISA = qw(Exporter); 86@EXPORT = qw(gensym ungensym qualify qualify_to_ref); 87@EXPORT_OK = qw(delete_package geniosym); 88 89$VERSION = '1.05'; 90 91my $genpkg = "Symbol::"; 92my $genseq = 0; 93 94my %global = map {$_ => 1} qw(ARGV ARGVOUT ENV INC SIG STDERR STDIN STDOUT); 95 96# 97# Note that we never _copy_ the glob; we just make a ref to it. 98# If we did copy it, then SVf_FAKE would be set on the copy, and 99# glob-specific behaviors (e.g. C<*$ref = \&func>) wouldn't work. 100# 101sub gensym () { 102 my $name = "GEN" . $genseq++; 103 my $ref = \*{$genpkg . $name}; 104 delete $$genpkg{$name}; 105 $ref; 106} 107 108sub geniosym () { 109 my $sym = gensym(); 110 # force the IO slot to be filled 111 select(select $sym); 112 *$sym{IO}; 113} 114 115sub ungensym ($) {} 116 117sub qualify ($;$) { 118 my ($name) = @_; 119 if (!ref($name) && index($name, '::') == -1 && index($name, "'") == -1) { 120 my $pkg; 121 # Global names: special character, "^xyz", or other. 122 if ($name =~ /^(([^a-z])|(\^[a-z_]+))\z/i || $global{$name}) { 123 # RGS 2001-11-05 : translate leading ^X to control-char 124 $name =~ s/^\^([a-z_])/'qq(\c'.$1.')'/eei; 125 $pkg = "main"; 126 } 127 else { 128 $pkg = (@_ > 1) ? $_[1] : caller; 129 } 130 $name = $pkg . "::" . $name; 131 } 132 $name; 133} 134 135sub qualify_to_ref ($;$) { 136 return \*{ qualify $_[0], @_ > 1 ? $_[1] : caller }; 137} 138 139# 140# of Safe.pm lineage 141# 142sub delete_package ($) { 143 my $pkg = shift; 144 145 # expand to full symbol table name if needed 146 147 unless ($pkg =~ /^main::.*::$/) { 148 $pkg = "main$pkg" if $pkg =~ /^::/; 149 $pkg = "main::$pkg" unless $pkg =~ /^main::/; 150 $pkg .= '::' unless $pkg =~ /::$/; 151 } 152 153 my($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/; 154 my $stem_symtab = *{$stem}{HASH}; 155 return unless defined $stem_symtab and exists $stem_symtab->{$leaf}; 156 157 158 # free all the symbols in the package 159 160 my $leaf_symtab = *{$stem_symtab->{$leaf}}{HASH}; 161 foreach my $name (keys %$leaf_symtab) { 162 undef *{$pkg . $name}; 163 } 164 165 # delete the symbol table 166 167 %$leaf_symtab = (); 168 delete $stem_symtab->{$leaf}; 169} 170 1711; 172