cannot acces variable inside while loop (in perl)

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 i开发者_StackOverflow社区n a naked block I follow with the error.

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

Any suggestion?

• 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.

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

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.