more ways are possible. You might profit the ternary operator described in perlop too: IF CONDITION ? THEN : ELSE

use strict;
use warnings;

my $scalar; # starts empty ie undef

                                                   # IF        THEN   
+   ELSE
print "\$scalar now holds the following value: [", $scalar ? $scalar :
+ 'UNDEF',"]\n";


# oops more correct as afoken pointed below:

print "\$scalar now holds the following value: [", defined $scalar ? $
+scalar : 'UNDEF',"]\n";

# update:
# infact, unless you check with 'defined' a zero can mislead you:
$scalar = 0;
print "\$scalar now holds the following value: [",  $scalar ? $scalar 
+: 'UNDEF',"]\n";
print "\$scalar now holds the following value: [", defined $scalar ? $
+scalar : 'UNDEF',"]\n";
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