in reply to detecting an undefined variable

I completely agree with the remarks of haukex, LanX and Athanasius regarding hashes, but if you just gotta do something like this, here's another way: 

c:\@Work\Perl\monks>perl -le
"use 5.010;
 ;;
 use strict;
 use warnings;
 ;;
 sub extscale ();
 ;;
 my $myscale = extscale // 1;
 print $myscale;
 ;;
 sub extscale () {
   no strict 'vars';
   no warnings 'once';
   return $scale;
   }
"
1

[download]
This is entirely a compile-time solution. Note that the  extscale function must be either declared (as above) or defined before it is used. Note also the use of a prototype to achieve the desired effect.

Give a man a fish:  <%-{-{-{-<

Replies are listed 'Best First'.
Re^2: detecting an undefined variable
by LanX (Saint) on Sep 21, 2019 at 15:25 UTC
    Nice!

    Here a generic - albeit slower - solution for definedness

    use strict;
use warnings;
use Data::Dump qw/pp dd/;

#my $scale =42;
#our $scale =42;

sub var {
    eval $_[0];# or die $@; 
}

my $myscale = var('$scale') // 1;

pp $myscale;

    [download]

    and inspecting the errorstring in $@ can help checking for existence instead.

    Global symbol "$scale" requires explicit package name (did you forget to declare "my $scale"?) at (eval 1) line 1.

    update
    of course using eval directly is shorter

    use strict;
use warnings;

#my  $scale =42;
#our $scale =42;

my $myscale = eval('$scale') // 1;

print $myscale;

    [download]

    but I prefer encapsulating such magic to be able to capture side effects like polluting $@ or potential injections by tainted input.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom