But the value was initialized (I mean variable was declared).

Declaring a variable (my $var;) and initialising a variable (my $var = 42;) are not the same thing. When a scalar variable is declared (without an initialiser) its given a value of undef. That's probably the source of your uninitialized value:

$ perl -we 'my $x; print $x'
Use of uninitialized value in print at -e line 1.
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I'm sure that if if you were to post some sample data somebody will offer better targetted help.