Boolean ?

[Julia De Silva]

Hi there all
I can do this in other languages. Have I got the syntax wrong or is this not
possible in Perl ?

my $testtime = 1107267063;
my $isbeforenow = ($testtime > time);
print"isbeforenow - $isbeforenow\n";

Output is >> isbeforenow -

TIA

J

 

[Arndt Jonasson]

I can do this in other languages. Have I got the syntax wrong or is this not
possible in Perl ?

my $testtime = 1107267063;
my $isbeforenow = ($testtime > time);
print"isbeforenow - $isbeforenow\n";

Output is >> isbeforenow -

You are assigning the result of a test to a variable, and printing it
out. Yes, you can - the value produced by logical operations to mean
"false" by Perl is the empty string, which is precisely what you're
getting.

Additional values are treated as "false" when being used in
tests. From "perldoc perlsyn":

The number 0, the strings C<'0'> and C<''>, the empty list C<()>, and
C<undef> are all false in a boolean context. All other values are true.

 

[A. Sinan Unur]

Hi there all
I can do this in other languages. Have I got the syntax wrong or is
this not possible in Perl ?

my $testtime = 1107267063;
my $isbeforenow = ($testtime > time);
print"isbeforenow - $isbeforenow\n";

Output is >> isbeforenow -

$isbeforenow is set to the empty string which is a false value in Perl.

You can do this:

my $isbeforenow = 0 + ($testtime > time);

if you really want to force the result to be numeric.

Sinan.

 

[Julia De Silva]

my $isbeforenow = 0 + ($testtime > time);

Excellent, just what I was after, thanks.

J

 

[Paul Lalli]

You can do this:

my $isbeforenow = 0 + ($testtime > time);

if you really want to force the result to be numeric.

An alternative suggestion would be to explicitly provide the two values
you want to have in your 'boolean' variable:

my $isbeforenow = $testtime > time ? 1 : 0;

Paul Lalli

 

[Anno Siegel]

$isbeforenow is set to the empty string which is a false value in Perl.

More precisely, comparisons return a scalar whose string value is empty
*and* whose numeric value is 0.

You can do this:

my $isbeforenow = 0 + ($testtime > time);

if you really want to force the result to be numeric.

If ($testtime > time) were just an empty string, you couldn't do this
under warnings.

Anno

 

[ioneabu]

Hey, your right. This produces an error:
#!/usr/bin/perl
use strict;
use warnings;

my $a = 0 + '';

 

[A. Sinan Unur]

(e-mail address removed)-berlin.de (Anno Siegel) wrote in @mamenchi.zrz.TU-Berlin.DE:

...
More precisely, comparisons return a scalar whose string value is
empty *and* whose numeric value is 0.

Thanks for catching that.

Sinan

 

[jl_post]

You can do this:

my $isbeforenow = 0 + ($testtime > time);

if you really want to force the result to be numeric.

Another alternative suggestion is this:

my $isbeforenow = ($testtime > time) || 0;

(This way it's guaranteed to be zero if it turns out
to be false.)

-- Jean-Luc