Perl, using variable from within While loop outside of the loop?

Question

This seems really simple but it is giving me a hard time figuring it out as I'm new to perl.. I've been looking through a lot of documentation now about loops and I am still stumped by this... I have a sub that contains a while loop and I want to use a variable value from within the loop outside of the loop (after the loop has run), however when I try to print out the variable, or return it out of the sub, it doesn't work, only when I print the variable from within the loop does it work.. I would appreciate any advice as to what I'm doing wrong.

Doesn't work (doesn't print $test ):

sub testthis {    
    $i = 1;
    while ($i <= 2) {    
        my $test = 'its working' ;    
        $i++ ;
    }
    print $test ;
}

&testthis ;

Works, prints $test:

sub testthis {
    $i = 1;
    while ($i <= 2) {
        my $test = 'its working' ;
        $i++ ;
        print $test ;
    }
}

&testthis ;

$i = 1; should probably be my $i = 1;, the way it is right now, you are talking to the variable $i in the outer scope which will be a source of errors as soon as you start calling subroutines from inside other subroutines. Chances are that $i is not even declared in the outer scope, in which case you are talking to the package variable. If you were running under use strict; use warnings; then the strict pragma would have thrown an error about the undeclared variable. — Eric Strom
– Eric Strom, Commented Jul 14, 2010 at 21:43

radius · Accepted Answer · 2010-07-14 09:13:06Z

10

You declare variable test inside the loop, so it scope is the loop, as soon as you leave the loop the variable is not longer declared.
Add my $test; just between $i=1 and while(..) and it will work. The scope will now be the entire sub instead of only the loop

answered Jul 14, 2010 at 9:13

radius

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1 Comment

Rick Over a year ago

ahh ok, I get it now.. thanks... the tutorials I've been looking at are too basic to even have mentioned this, I suppose I should go straight to the perl man pages from now on

Abel · Accepted Answer · 2010-07-14 09:13:10Z

5

Place my $test before the while loop. Note that it will only contain the last value that is assigned in the while loop. Is that what you are after?

// will print "it's working" when 'the loop is hit at least once,
// otherwise it'll print "it's not working"
sub testthis {
    $i = 1;
    my $test = "it's not working";

    while ($i <= 2) {
        $test = "it's working";
        $i++ ;
    }
    print $test ;
}

answered Jul 14, 2010 at 9:13

Abel

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Comments

Nikhil Jain · Accepted Answer · 2010-07-14 09:16:01Z

3

you can try this one:

sub testthis {
my $test
$i = 1;
while ($i <= 2) {

$test = 'its working' ;

$i++ ;

print $test ;
}

}

&testthis ;

Note: whenever write perl code, its better to add use strict; and use warning in the beginning of the code.

answered Jul 14, 2010 at 9:16

Nikhil Jain

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