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From: pfeiffer@cix.cict.fr (Daniel Pfeiffer)
Newsgroups: comp.unix.shell
Subject: Re: for loops
Keywords: sh, for, count
Message-ID: <1477@irit.irit.fr>
Date: 16 Apr 91 13:16:47 GMT
Sender: pfeiffer@irit.fr
Organization: Instituto de Reser^cado pri Informadiko de Tuluzo (IRIT)
	      Universitato Paul Sabatier
Lines: 56


What I don't like about the expr example, is the number of times
we need to fork, since it's not a builtin.  The following, adapted
from a proposal one or two months back is a bit hard to understand,
(documented at the end) but should be lots quicker:

$ FILES=5
$ for i in `echo "[p 1 + d $FILES!<P] sP 1 lP x" | dc`
> do
> echo $i
> done
1
2
3
4
5
$ 

Someone also proposed a comparable script for awk, but, given that awk
is a rather huge language, I suppose that dc is quicker. Alternately,
for better readability, you might say

count() {
	echo "[p 1 + d $1 !<P] sP 1 lP x" | dc
}

for i in `count 5`

You can also twiddle the first 1 to change the increment, or the
second 1 to change the starting point, as in the following script:

#! /bin/sh
if [ ! "$1" ]; then
	echo "usage:  count number
	count beg end [step]">&2
	exit 1
elif [ $# = 1 ]; then
	set 1 $1
fi
# Program [ print top, increment top, duplicate, push end, pop and compare
#	two top values, reexecute P if not past end ]
# store program as P, push beginning, load P, execute it
echo "[p ${3-1} + d $2 !<P] sP $1 lP x" | dc

--
-- Daniel Pfeiffer				<pfeiffer@cix.cict.fr>
-- Tolosa (Toulouse), Midi-Pyrenees, Europe	<pfeiffer@irit.fr>
-- "Beware - polyglot esperantist"		<pfeiffer@frcict81.bitnet>
--

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