in reply to conditional definition of variables

my $var="zzz\n" unless defined($var)

This is the problem; the behavior of a my declaration in a statement with a conditional modifier is undefined. This is documented in perldoc perlsyn. Convert that to an unless statement: 

unless ( defined $var) { my $var = "zzz\n" }

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and you will get predictable behavior, but, probably, not what you want.

I don't know what you are trying to do, but you might consider using a hash to hold the set of variables that may or may not exist.

Be well,
rir

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Re^2: conditional definition of variables
by JadeNB (Chaplain) on Aug 26, 2008 at 23:20 UTC
    unless ( defined $var) { my $var = "zzz\n" } and you will get predictable behavior, but, probably, not what you want.
    To expand on what you said, the OP should note that, since the my $var inside the unless has nothing to do with the my $var outside, so this code would leave the outer $var alone, whether or not it's defined. As mentioned by betterworld, just omitting the second my (whether you use the unless in modifier or BLOCK form) gives the (probably-)desired effect of modifying the outer $var.
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