Saxium:

If you simply remove the 'my' from the second assignment to $x, you'll have a single $x variable, and the program will do what you're expecting.

Update: Added the sentence in parenthesis.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

use warnings;

"my" variable $x masks earlier declaration in same scope at ./monks.pl
+ line 7.
main::printme() called too early to check prototype at ./monks.pl line
+ 6.
main::printme() called too early to check prototype at ./monks.pl line
+ 8.
Use of uninitialized value $x in concatenation (.) or string at ./monk
+s.pl line 11.
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Hello Saxium, and welcome to the Monastery!

The following quote from perlsub may throw a little more light on the answer given by roboticus:

A my has both a compile-time and a run-time effect. At compile time, the compiler takes notice of it. The principal usefulness of this is to quiet use strict 'vars', but it is also essential for generation of closures as detailed in perlref. Actual initialization is delayed until run time, though, so it gets executed at the appropriate time, such as each time through a loop, for example.

So the rationale behind the behaviour described by roboticus — The printme subroutine uses the ... [$x] in scope at the point where it's compiled. — is to facilitate closures as a feature of Perl. Here are some references on closures, in case you’re interested:

• Whats-a-closure of perlfaq7
• “Persistent variables with closures” in perlsub
• Section 4 of perlref#Making-References
• Closure on Closures by broquaint

Excellent question, by the way!

Hope that helps,

And also it would be better to pass your variable as an argument to the subroutine, rather than using is as a global variable, for example with something like this:

#!/usr/bin/perl
use strict;
use warnings;

my $x = 'a';
printme($x);
$x = 'b';
printme ($x);

sub printme {
   print "x: ", shift, "\n";
}
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x: a
x: b
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Slightly OT: The other warnings shown in monkey_boy's example of running your code with warnings enabled, the ones about "main::printme() called too early to check prototype...", can be silenced by either declaring or defining the prototyped subroutine before the subroutine is ever invoked:

c:\@Work\Perl\monks>perl -wMstrict -le
"sub printme();
 ;;
 my $x = 'a';
 printme();
 ;;
 $x = 'b';
 printme();
 ;;
 sub printme () {
   print qq{x: '$x'};
   }
"
x: 'a'
x: 'b'
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