If you're using Bash or similar for the shell on the other end, how about doing:

my @result = $object->cmd('test -f foo.txt; echo $?')
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Because in Bash $? holds the exit value of the last command, and test -f checks to see if the file given exists and is a regular file, $result[0] should contain either a 1 (file does not exist) or a 0 (file does exist). After you determine that, you can cat your file or display the appropriate error.