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Perl 5 version 18.1 documentation
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Symbol - manipulate Perl symbols and their names


  1. use Symbol;
  2. $sym = gensym;
  3. open($sym, "filename");
  4. $_ = <$sym>;
  5. # etc.
  6. ungensym $sym; # no effect
  7. # replace *FOO{IO} handle but not $FOO, %FOO, etc.
  8. *FOO = geniosym;
  9. print qualify("x"), "\n"; # "main::x"
  10. print qualify("x", "FOO"), "\n"; # "FOO::x"
  11. print qualify("BAR::x"), "\n"; # "BAR::x"
  12. print qualify("BAR::x", "FOO"), "\n"; # "BAR::x"
  13. print qualify("STDOUT", "FOO"), "\n"; # "main::STDOUT" (global)
  14. print qualify(\*x), "\n"; # returns \*x
  15. print qualify(\*x, "FOO"), "\n"; # returns \*x
  16. use strict refs;
  17. print { qualify_to_ref $fh } "foo!\n";
  18. $ref = qualify_to_ref $name, $pkg;
  19. use Symbol qw(delete_package);
  20. delete_package('Foo::Bar');
  21. print "deleted\n" unless exists $Foo::{'Bar::'};


Symbol::gensym creates an anonymous glob and returns a reference to it. Such a glob reference can be used as a file or directory handle.

For backward compatibility with older implementations that didn't support anonymous globs, Symbol::ungensym is also provided. But it doesn't do anything.

Symbol::geniosym creates an anonymous IO handle. This can be assigned into an existing glob without affecting the non-IO portions of the glob.

Symbol::qualify turns unqualified symbol names into qualified variable names (e.g. "myvar" -> "MyPackage::myvar"). If it is given a second parameter, qualify uses it as the default package; otherwise, it uses the package of its caller. Regardless, global variable names (e.g. "STDOUT", "ENV", "SIG") are always qualified with "main::".

Qualification applies only to symbol names (strings). References are left unchanged under the assumption that they are glob references, which are qualified by their nature.

Symbol::qualify_to_ref is just like Symbol::qualify except that it returns a glob ref rather than a symbol name, so you can use the result even if use strict 'refs' is in effect.

Symbol::delete_package wipes out a whole package namespace. Note this routine is not exported by default--you may want to import it explicitly.


Symbol::delete_package is a bit too powerful. It undefines every symbol that lives in the specified package. Since perl, for performance reasons, does not perform a symbol table lookup each time a function is called or a global variable is accessed, some code that has already been loaded and that makes use of symbols in package Foo may stop working after you delete Foo , even if you reload the Foo module afterwards.