What is this NULL you speak of? Perhaps you have the wrong language? There is no NULL in Perl...

You probably want undef. That's the Perl equivalent of C/C++'s NULL. Check out defined.

if (defined $value)
{
  Do that
}
else
{
  Do this
}
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You can use not to reverse that.

Actually C doesn't have NULL either. It just has various (sometimes incompatible) variations on #define NULL 0. However 0 as a value for pointers in C is magical in a sort of similar fashion to the magic represented by undef in Perl.

---

DWIM is Perl's answer to Gödel

Check the C standard. It has a NULL. How it's implemented is implementation defined, which means it could be anything. Section 7.1.6 of the 1990 standard (yes, there's a 1999 standard - I don't have a copy of that) includes the text:

The macros are


NULL


which expands to an implementation-defined null pointer constant

You're confusing C with C++ which defines NULL to be equivalent to the integer constant 0. Normally in C, the define is actually (void*)0.

Perl tries to make things as easy as possible for you and this is a good example.

In most cases, what you actually want is as simple as:

if ($value) {
  # $value contains something useful
} else {
  # $value is "empty"
}
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(Note that the logic is reversed from your original example)

What we're doing here is checking the "truth" of $value. $value will be "false" if it contains any of the following values:

• "undef" (i.e. if it hasn't been given a value)
• The number 0
• The string "0"
• The empty string ("")

Any other value in $value will evaluate to "true".

This is all you need in most cases. There are a couple of "corner cases" that you sometimes have to consider:

• Sometimes 0 is an acceptable value. You account for that by using if ($value or $value == 0).
• Sonetimes you might want to test that $value contains nothing but whitespace characters. The easiest way to do that is by checking for the presence of non-whitespace characters with if ($value =~ /\S/).

Sometimes 0 is an acceptable value. You account for that by using if ($value or $value == 0).

This may be more inclusive than you wish. (it will be true for both undef and the empty string), as it's basically asking for everything that's true or everyhing that's false. You likely wanted eq instead of == :

($value or $value eq 0)
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Well the answer depends on how you get the value from the "box". Most UI components return empty input as an empty string, but some might return undef instead.

# let's say you've got the user input in $input..

if (defined($input) && $input ne "") {
  # input is defined and not empty
}
else {
  print "input wasn't filled in\n";
}
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Note that compare strings with eq and ne instead of == and != since == and != coerce their arguments to numbers.

See equality operators and defined in the documentation.

"What should it profit a man, if he should win a flame war, yet lose his cool?"

Your awesome!!
Thanks so much for your help, for some reason I just forgot about "EQ and NE"
Duh!

if ( True( $value ) ) {
}
else {
}

sub True {
    defined $_[0]
      and $_[0]
      and ( uc( $_[0] ) ne "NULL" )
      # and $_[0] !~ /^N\/?A$/
      ;
}
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