in reply to Capture error from one-liner

At it's simplest, could it not be ... 
set -e
[ -f $fname ] && [ -r $fname ]
perl -i.bak -pe 's/AJZ/AZZ/g if /^AB/' $fname

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Just a thought ...

A user level that continues to overstate my experience :-))

In Section Seekers of Perl Wisdom