1). Depends if the program is run with warnings on or not (-w option). If it is then:

"our" variable $test masks earlier declaration in same scope
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More likely the interviewer wanted you to say what the difference between my, our, and local is.

2). The interviewer probably wanted PERL5LIB or PERLLIB, but actually any environment variable could be used to set the path provided you

use lib $ENV{varname};
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Did you get the job?