There are three potential levels of 'blankness' that you should be checking for.

1. Variable has never been given a value.
   Test with unless (defined $foo)
2. Variable contains an empty string.
   Test with if ($foo eq '') (note that you could simplify it to unless ($foo) if you could be sure that zero wasn't a valid value.)
3. Variable contains only whitespace.
   Test with if ($foo =~ /\S/)

Update Thanks to merlyn for pointing out the error in the second bullet point - which I've now corrected.

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

Re Bullet 3:


my $foo = " bar";
if($foo =~ /\S/) {
  print "Whitespace only\n";
}
[download]

I think you meant:


my $foo = " bar";
if($foo =~ /^\s+$/) {
  print "Whitespace only\n";
}
[download]

Update: Whoops, davorg is right (see below)... and easier to see. I was thinking \s instead of \S. Fixed above, but hokey, so use his code instead.
--isotope
http://www.skylab.org/~isotope/

Actually it should have been unless ($foo =~ /\S/) to maintain the same logic as the other examples.

I think you may be confusing \s (whitespace) with \S (non-whitespace).

--
<http://www.dave.org.uk>

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

If you also want to flag strings that contain only whitespace, a regex is appropriate: $foo =~ /^\s*$/ or $foo !~ /\S/.

(In any solution, you may want to test with defined() first to avoid uninitialized value warnings.)

For example, do you want to do something 'kool' or 'not so kool' if $foo was "0"?

In general you're probably not wanting to check just for an empty string, but for "truth".

In that case you can then just do:

if ($foo) {
 ...
} else {
 ...
}
[download]

Tony

I don't see anything wrong with your construct and I would think a regex would make the code less readable in some circles. Depending on $/, /^$/ would check for an empty string as well. So if you're replacing blank variables you could do s/^$/Hi there/.

if ( ! defined($foo) ) {
     #do something kool
  }
  else {
     #do something not so kool
  }
[download]

That wouldn't do what is intended. Look at these cases...

my $var1;
my $var2 = undef;
my $var3 = "";
my $var4 = 0;
my $var5 = 1;
my $var6 = "foo";

for ($var1,$var2,$var3,$var4,$var5,$var6) {
  print defined($_)?1:0 . "\t" .
    ($_)?1:0 . "\n";
}

__END__
Output:
0   0
0   0
1   0
1   0
1   1
1   1
[download]

yeah, i guess you're right, because it returned true with $var3...but as for $var4 and $var5, the ($_)?1:0 is checking if they're TRUE or FALSE, not whether they're defined. still, i get your point.

______________________________________________
If the world didn't suck, we'd all fly off.
       -A friend of mine

There is much to think on here beyond simply testing for "". ^-^

It's nice to know that once in a while, a poor scribe's craft is not always doing A Bad Thing(tm) :)

Thanks again.

saiyuk