Hi,

I am confused about the behavior of the subroutine that used a variable, which was declared by "my" twice in main.

use warnings;

my $s = "s1";
print "define var: $s\n";
&test;

my $s = "s1-2nd";
print "define var: $s\n";
&test;

sub test{
        print "sub: $s\n";
}
[download]

Result from the above code:

"my" variable $s masks earlier declaration in same scope at test.pl li
+ne 8.
define var: s1 
Use of uninitialized value $s in concatenation (.) or string at test.p
+l line 13.
sub:
define var: s1-2nd
sub: s1-2nd
[download]

So the second call of &test didn't have the $s value. If I only used one "my" at the beginning (i.e. use $s = "s1-2nd", instead of my $s = "s1-2nd"), it behaved like I expected, the subroutine &test gave the value of $s each time it was called. But as shown above, by just adding "my" and declaring the $s second time, the first call of &test had $s value as uninitialized. Why did this happen?

If I placed the subroutine at the beginning, such as:

use warnings;

my $s = "s1";
print "define var: $s\n";
&test;

sub test{
        print "sub: $s\n";
}

my $s = "s1-2nd";
print "define var: $s\n";
&test;
[download]

This time, the result is:

"my" variable $s masks earlier declaration in same scope at test.pl li
+ne 12.
define var: s1
sub: s1
define var: s1-2nd
sub: s1
[download]

So the second call of &test did have the $s value but the value was from the first declaration. Why did the second $s value not overwrite the first when there is a second "my"?
Again, if I simply remove the second "my", the result would be expected:

define var: s1
sub: s1
define var: s1-2nd
sub: s1-2nd
[download]

Thanks in advance for your kind reply.

ark