[not-quite-serious-mode]

Ha! This is perhaps the first time i find something to nit-pick in anything the infallible Don has pontificated. Actually it is posssible to do arithmetic in sed. Here, for example, is addition/subtraction (from stackoverflow):

Code:

s/[0-9]/<&/g
s/0//g
s/1/|/g
s/2/||/g
s/3/|||/g
s/4/||||/g
s/5/|||||/g
s/6/||||||/g
s/7/|||||||/g
s/8/||||||||/g
s/9/|||||||||/g
: tens
s/|</<||||||||||/g
t tens
s/<//g
s/+//g
: minus
s/|-|/-/g
t minus
s/-$//
: back
s/||||||||||/</g
s/<\([0-9]*\)$/<0\1/
s/|||||||||/9/
s/||||||||/8/
s/|||||||/7/
s/||||||/6/
s/|||||/5/
s/||||/4/
s/|||/3/
s/||/2/
s/|/1/
s/</|/g
t back

In fact, sed is a (Turing-) complete programming language. This can be shown by either writing a Turing-machine in sed (shown here) or by writing an interpreter for another Turing-complete language. With much fanfare, here is a Brainfuck-interpreter written in sed.

[/not-quite-serious-mode]

I hope this helps (well, actually i doubt it, but this is a holiday where i am, so it is a day off and it is fun).

bakunin

PS: Input to the sed-script above would be "100+15" or "250-173"