I've never been on an AIX system, but since it's "based on" unix, I would check whether the env. variable is marked for "export" when it is set. This may have more to do with the shell you're using (to run the perl script), rather than the OS.

In bourne-type shells, it's a difference between:

# setting an unexported env. variable:
VARIABLE='some value'

# vs.
export VARIABLE='some value'
# or
VARIABLE='some value'
export VARIABLE
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