POSIX not really relevant, more systems? Debatable. More implementations could be seen as a negative. Perl is more regular than Awk for the simple cases and

POSIX not really relevant, more systems? Debatable. More implementations could be seen as a negative. Perl is more regular than Awk for the simple cases and is more usable for anything that isn't merely iterating over input. Of course, you shouldn't any of awk/perl/shell for tasks that aren't being run by you or are over say 20 lines long.