Symbol(3pm) Perl Programmers Reference Guide Symbol(3pm)
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.
perl v5.38.2 2023-11-28 Symbol(3pm)
perl 5.38.2 - Generated Tue Dec 10 18:29:06 CST 2024