Difference between $MAIL::xyz == 0 and $MAIN::xyz == '0'

[kris2002]

My Questions :

1. I would like to know the difference between $MAIN::xyz == 0 and $MAIN::xyz == '0'.


2. Is MAIN a key word in Perl?

3. A situation in our program, $MAIN::xyz is not set to any value any where. At some point, I see a if ($MAIN::xyz == 0) condition. I can see that while the code is executed, it does go in to this condition (the condition getting satisfied i.e). Is this statement getting evaluated as "Whether the $MAIN::xyz exists or not" OR is it being evaluated as "$MAIN::xyz has a value of 0 or not".

It is a bit confusing. Any body can throw light on this one? Thanks in advance.

 

[kris2002]

SORRY, the subject line should read "MAIN" rather than "MAIL". Thanks.

 

[mikevh]

1. $MAIN::xyz == 0 tests whether the variable $xyz in the package MAIN is equal to zero.
$MAIN::xyz == '0' is incorrect, since it's using the numeric comparison operator == to test whether $xyz is equal to the string '0'. The string comparison operator is eq.

2. MAIN is not a keyword in Perl. However main (lowercase) is the default package name, i.e., this is the package name when no other package name is specified.
MAIN is not the same as main.

If $MAIN::xyz doesn't exist, it would not have a value of 0. It would be undefined.