http://www.perlmonks.org?node_id=1040602


in reply to Test if multiple variables are defined

Two short ways would be:

defined and s/^\s+|\s+$//g for ( $ipaddress, $prefix, $interface, $dev
+ice, $location, $comment );

[download]

defined ? s/^\s+|\s+$//g : 1 for ( $ipaddress, $prefix, $interface, $d
+evice, $location, $comment );

[download]

In the first case you use the fact that and does not execute the second operand if the first one is false. In the second case, test ? instr1 : instr 2; is syntactic sugar for if (test) { instr1; } else { instr2; }. You do have to write a second instruction though, and since Perl doesn't provide a no-op instruction (but you can make one), the 1 in my example can't be omitted.

Replies are listed 'Best First'.
Re^2: Test if multiple variables are defined
by stroke (Acolyte) on Jun 25, 2013 at 14:12 UTC

    Do either of these perform the check on all the variables and then only execute if they are all defined? Example: $ipaddress is defined, $prefix is defined, $interface is undef. I still want to run the substitution on $ipaddress, $prefix, so effectively have the variables defined state unrelated.

    Hence, I think I may need to do it separately?

[reply]

      Here is the longer version of the same code: 

      for ( $ipaddress, $prefix, $interface, $device, $location, $comment )
{
  defined and s/^\s+|\s+$//g;
  # or defined ? s/^\s+|\s+$//g : 1; It does the same thing
  # or even if (defined) { s/^\s+|\s+$//g } 
  
  ## Edit : and there is
  # s/^\s+|\s+$//g if defined; 
  ## That one is quite nice.
  ## Let's just say there's more than one way to do it.
}

      [download]
      So yeah, the instructions inside the block are run on each element, and not the array as a whole.

      If you have to ask though, I'd advise you to go for the long version because it will run just as fast, it's just another way of writing the same thing. Here is another way to do it, which I find easy to read thanks to the next keyword. 

      STRING: for( $ipaddress, $prefix, $interface, $device, $location, $com
+ment )
{
  next STRING unless defined; # We skip any element that is not define
+d
  s/^\s+|\s+$//g;
}

      [download]

[reply]
[d/l]
[select]

        Thanks, that's what I was trying to say - run it on each element, not the array as a whole. Words failed me at the time though. And a simple solution - I went for:

        for ( $ipaddress, $prefix, $interface, $device, $location, $comment ) 
+{
  s/^\s+|\s+$//g if defined;
}

        [download]

        Thanks for your wisdom!

[reply]
[d/l]

In Section Seekers of Perl Wisdom