Identify empty string in Perl

Question

There is probably an easy solution to this, but I can't figure it out. I am looking to:

• take a CSV file into an array
• loop through the array and split fields into variables
• if the array field is empty then set the variable to "N/A"

Note: It is only setting the $variable to "N/A" that I cannot get working.

For example:

foreach $var (@list) {

($name,$date,$size, etc...)=split(/,\"/,$var);

}

How would I set $date to "N/A" if the field in the array is empty?

so to produce:

$name = Jim
$date = N/A
$size = small

I hope this makes sense and is easy to fix. -Thanks

Answer 1

Assuming the variable $date is undefined when "empty":

if (!defined($date)) {
  $date = 'N/A';
}

Or more concisely:

$date //= 'N/A';

Or if it really is an empty string, i.e. $date = ''; (this will also work in the case where $date is undefined, but you don't want to use this if you only want to identify the case where it is undefined):

if ($date eq '') {
  $date = 'N/A';
}

Or more concisely (note that this will also set $date to N/A if $date is '0' due to Perl's weak typing):

$date ||= 'N/A';

Answer 2

1. As far as your third bullet point and the actual question: to check for emptiness:

   • For empty string, you can either do the above-mentioned eq "", or you can check the string length: $var = "N/A" unless length($var);;

   • For an undefined of empty string, in Perl 5.10 you can use the "defined-or" (//) operator to do the short version: $var = "N/A" unless length($var // '');

   • In Perl before 5.10 where "defined-or" is not available, you will either have to spell out the defined check: $var = "N/A" unless defined $var && length($var);

   • ... or, you can just stop caring about undefined warnings by turning them off (h/t brian d foy):

     no warnings 'uninitialized';
     $_ = "N/A" unless length($_) foreach ($name,$date,$size, etc...);
     use warnings 'uninitialized'; # Always turn back on.
     

2. However, please note that you also should consider a different approach to the first two bullet points. Implementing your own CSV parser which is 100% correct is not trivial - for example, your sample code will break if any of the fields contain a double quote.

   Instead, you should always use one of the standard Perl CSV parsers, such as Text::CSV_XS.