Packages

Only identifiers starting with letters are stored in the packages symbol table. All other symbols are kept in package "main". In addition, the identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT, ENV, INC and SIG are forced to be in package "main", even when used for other purposes than their built-in one. Note also that, if you have a package called "m", "s" or "y", the you can't use the qualified form of an identifier since it will be interpreted instead as a pattern match, a substitution or a translation.

Eval'ed strings are compiled in the package in which the eval was compiled in. (Assignments to $SIG{}, however, assume the signal handler specified is in the main package. Qualify the signal handler name if you wish to have a signal handler in a package.) For an example, examine perldb.pl in the perl library. It initially switches to the DB package so that the debugger doesn't interfere with variables in the script you are trying to debug. At various points, however, it temporarily switches back to the main package to evaluate various expressions in the context of the main package.

The symbol table for a package happens to be stored in the associative array of that name prepended with an underscore. The value in each entry of the associative array is what you are referring to when you use the *name notation. In fact, the following have the same effect (in package main, anyway), though the first is more efficient because it does the symbol table lookups at compile time:

	local(*foo) = *bar;
	local($_main{'foo'}) = $_main{'bar'};

	package dumpvar;

	sub main'dumpvar {
	    ($package) = @_;
	    local(*stab) = eval("*_$package");
	    while (($key,$val) = each(%stab)) {
	        {
	            local(*entry) = $val;
	            if (defined $entry) {
	                print "\$$key = '$entry'\n";
	            }
	            if (defined @entry) {
	                print "\@$key = (\n";
	                foreach $num ($[ .. $#entry) {
	                    print "  $num\t'",$entry[$num],"'\n";
	                }
	                print ")\n";
	            }
	            if ($key ne "_$package" && defined %entry) {
	                print "\%$key = (\n";
	                foreach $key (sort keys(%entry)) {
	                    print "  $key\t'",$entry{$key},"'\n";
	                }
	                print ")\n";
	            }
	        }
	    }
	}