cannot acces variable inside while loop (in perl)

Question

A very easy question on variables scope. I have a variable defined in the main code that I use inside a while loop.

my $my_variable;
while(<FILE>) {
   ...using $my_variable
}
if ($my_variable) -> FAILS

When I exit the loop and use the variable I get an error:

Use of uninitialized value $my_variable

Even if I enclose the variable in a naked block I follow with the error.

{
    my $my_variable;
    while(<FILE>) {
       ...using $my_variable
    }
    if ($my_variable) -> FAILS
}

Any suggestion?

Could you provide a complete example that can be copied verbatim that shows the problem? Are you using strict? — musiKk
– musiKk, Commented Mar 22, 2011 at 12:26
I agree with musiKk. Even more importantly are you using use strict; use warnings;? If not do it and see if it gives you some warning. — Joel Berger
– Joel Berger, Commented Mar 22, 2011 at 14:03
Please provide real code that can be run and exhibits the error you are seeing. The code in your question can't be run, and even if it could, it would not output the warning message in your question. — Ven'Tatsu
– Ven'Tatsu, Commented Mar 22, 2011 at 14:16
@Joel: If OP is receiving "use of uninitialized value" warnings, then he definitely has warnings turned on, at least. — Dave Sherohman
– Dave Sherohman, Commented Mar 22, 2011 at 16:03

Axeman · Accepted Answer · 2011-03-22 15:08:06Z

1

Are you using $my_variable in the loop or did you redefine it as my $my_variable somewhere in the loop. You'd be surprised how easily a my slips in to variable assignment.

I even have a frequent tick in my code where I write something like
```
 my $hash{ $key } = ... some elaborate assignment;
```
Also, if should not complain about an uninitialized variable. undef => Boolean false.
I wouldn't worry about initializing all my variables -- but its crucial that you learn a mindset about how to use undefs. And always, always USUW (use strict; use warnings) so that variables aren't uninitialized when you don't expect them to be.

answered Mar 22, 2011 at 15:08

Axeman

29.9k2 gold badges50 silver badges104 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

green69 Over a year ago

OK actually I was having a bug that was messing up the process inside my while loop. Following your suggestions I discover the bug and make the script work. Thank you all!

green69 Over a year ago

Defining a variable outside while loop (with my $my_variable) and using it inside the while loop without re-defining it (without "my") then it's possible to use the value of $my_variable even outside the loop.

musiKk · Accepted Answer · 2011-03-22 12:17:34Z

1

Do you ever assign to $my_variable? All you show is a declaration (the my) and a usage (the if) but never an assignment.

answered Mar 22, 2011 at 12:17

musiKk

15.3k4 gold badges60 silver badges85 bronze badges

Comments

Toto · Accepted Answer · 2011-03-22 12:17:49Z

0

In the examples given, you didn't initialize $my_variable so it is undefined after the while loop.

You can do my $my_variable = ''; just before the loop.

answered Mar 22, 2011 at 12:17

Toto

91.7k63 gold badges97 silver badges135 bronze badges

2 Comments

green69 Over a year ago

OK, so I can't try to access $my_variable (modified inside the loop) outside the loop, because is out of scope. So, I can I do it?

Toto Over a year ago

If you modify $my_variable inside the loop (ie assign a defined value) you can use it outside the loop. Could you show us the code inside the loop ? May be you never assign a defined value.

Collectives™ on Stack Overflow

cannot acces variable inside while loop (in perl)

3 Answers 3

2 Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related