NAME¶
Symbol - manipulate Perl symbols and their names
SYNOPSIS¶
use Symbol;
$sym = gensym;
open($sym, "filename");
$_ = <$sym>;
# etc.
ungensym $sym; # no effect
# replace *FOO{IO} handle but not $FOO, %FOO, etc.
*FOO = geniosym;
print qualify("x"), "\n"; # "main::x"
print qualify("x", "FOO"), "\n"; # "FOO::x"
print qualify("BAR::x"), "\n"; # "BAR::x"
print qualify("BAR::x", "FOO"), "\n"; # "BAR::x"
print qualify("STDOUT", "FOO"), "\n"; # "main::STDOUT" (global)
print qualify(\*x), "\n"; # returns \*x
print qualify(\*x, "FOO"), "\n"; # returns \*x
use strict refs;
print { qualify_to_ref $fh } "foo!\n";
$ref = qualify_to_ref $name, $pkg;
use Symbol qw(delete_package);
delete_package('Foo::Bar');
print "deleted\n" unless exists $Foo::{'Bar::'};
DESCRIPTION¶
"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.
BUGS¶
"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.