Re: Checking Variable for Not Null

First, you have the logic back-to-front; you want:

next if !$ex_date;
next if !defined($ex_date);
[download]

next unless ex_date;
next unless defined($ex_date);
[download]

Second, the two statements are not equivalent. The first will skip to the next record if $ex_date has the value of 0 (zero), "" (the null string), or undef. See perlsyn#Truth-and-Falsehood. The second statement will skip only if $ex_date is undef.

Which form to use depends on how you define “null.” If by null you mean false, then use the first form; but if you mean undefined, then the second form is the one you want. Without more information, it’s difficult to guess which meaning of “null” best suits your needs; but the second interpretation (null means undef) is usually the safer option.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

Comment on Re: Checking Variable for Not Null Select or Download Code

Replies are listed 'Best First'.

Re^2: Checking Variable for Not Null
by dirtdog (Monk) on May 27, 2015 at 15:09 UTC

Hi, what i mean by null in this case is i'm checking a date position in a file (for example position 140-148). If there is no date passed:

$ex_date=substr($_,140,8);$ex_date =~ s/\s+$//;
[download]

then i would want to skip to the next record.

[reply]
[d/l]

Re^3: Checking Variable for Not Null

by Athanasius (Archbishop) on May 27, 2015 at 15:17 UTC

In that case, your “null” corresponds to the empty string, so you can test for true or false (because the empty string is “false” in Perl):

next if !$ex_date;
[download]

But it’s better (because clearer) to make the test explicit:

next if length $ex_date == 0;
# or
next if $ex_date eq "";
[download]

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,