As an aside, your regex does not do what you probably think it does.

/AZII*/ checks whether there is a literal string "AZII" followed by zero or more characters "I" in $line. If you want to check for the literal string "AZII*" then you must escape the "*" as it has special meaning in a regex: /AZII\*/. It probably did not hurt you here, unless somewhere in the binary data was a sequence of bytes which translates to "AZII".

Update: Changed "AZII" to "AZI" as per apl's and johngg's (in CB) comments.