You are assuming that the current operating system has the "cat" command, and has it in the current $PATH (or whatever Windows uses).
It also costs a fork/exec which seems very costly to me compared to opening and slurping in a file.
It may be fewer characters to type, but it probably gets terrible performance (where that's a concern) and is not portable (where that's a concern).
I distinctly remember some package having a simple file slurp method which makes this even simpler, but I don't remember if it was specific to an Apache related module or if it could be used in any environment. Not too hard to write one if you do this often, though.
Oh, yeah, just because a file exists (-f) doesn't mean that it is readable. You might want to change the code to use -r to decrease the risk that the cat command will fail.
On the topic of "sort", I have been known to recommend running the external command instead of doing a sort inside of Perl. It mainly depends on how large the data set is and how complex the sorting criteria.
-- Eric Hammond