Scalar::Util

Implements a few useful scalar-related subroutines. Like List::Util, Scalar::Util is something useful that doesn't necessarily fit well as a keyword in the Perl core. By default, Scalar::Util does not export any subroutines. As of Perl 5.8, Scalar::Util is shipped with the source kit.

Scalar::Util implements the following methods.

blessed expr 

Evaluates whether expr is a blessed reference. If successful, blessed returns the name of the package. Otherwise, blessed returns undef.

use Scalar::Util qw(blessed); use CGI; my $cgi = CGI->new(); my $not_cgi = "IamNotCGI"; my $is_blessed = blessed($cgi); if(defined($is_blessed) {
 print "$cgi\n;"
}
# Prints CGI my $is_blessed2 = blessed($not_cgi); if(defined($is_blessed2) {
 print "$not_cgi\n";
}
# undef

dualvar number, string 

Returns a string that has the value numberin a numeric context and a value string in a string context. For example:

my $context = dualvar(10, "Nathan"); my $add_nums = $context + 1; # '11' my $str_add = $context . "Patwardhan"; # Nathan Patwardhan

isweak expr 

Returns true if expr is a scalar, which is a weak reference:

my $weak_ref = \$boo_hoo; my $i_am_weak = isweak($weak_ref); # false weaken($weak_ref); $i_am_weak = isweak($weak_ref); # true

openhandle fh 

Returns fh if fh is an open filehandle. fh may also be a tied filehandle. Returns undef on failure.

my $fh = openhandle(*STDIN); $fh = openhandle("sumfin"); # undef, since sumfin isn't # open

readonly scalar 

Returns true if scalar is read-only.

reftype expr 

Returns the reference type of expr if expr is a reference. Otherwise, returns undef.

my $r_type = reftype "ORA"; # undef, not a reference my $r_type = reftype []; # ARRAY

tainted expr 

Returns true if the result of expr is tainted:

my $is_tainted = tainted($ENV{PATH}); # Returns true if -T is enabled

weaken ref 

Returns ref into a weak reference. When the reference count on an object reaches 0, ref will be set to undef.