In Perl, how can I concisely check if a $variable is defined and contains a non zero length string?

Question

I currently use the following Perl to check if a variable is defined and contains text. I have to check defined first to avoid an \'uninitialized value\' warnin

Answer 1

First, since length always returns a non-negative number,

if ( length $name )

and

if ( length $name > 0 )

are equivalent.

If you are OK with replacing an undefined value with an empty string, you can use Perl 5.10's //= operator which assigns the RHS to the LHS unless the LHS is defined:

#!/usr/bin/perl

use feature qw( say );
use strict; use warnings;

my $name;

say 'nonempty' if length($name //= '');
say "'$name'";

Note the absence of warnings about an uninitialized variable as $name is assigned the empty string if it is undefined.

However, if you do not want to depend on 5.10 being installed, use the functions provided by Scalar::MoreUtils. For example, the above can be written as:

#!/usr/bin/perl

use strict; use warnings;

use Scalar::MoreUtils qw( define );

my $name;

print "nonempty\n" if length($name = define $name);
print "'$name'\n";

If you don't want to clobber $name, use default.