for loops

[Rob Tulloh]

miquels at maestro.htsa.aha.nl (Miquel van Smoorenburg) writes:

>In article <3693 at ux.acs.umn.edu> edh at ux.acs.umn.edu (Merlinus Ambrosius) writes:
>>In sh, I'd like to do something like a BASIC for loop.  Say I have $FILES
>>set to some number, and I'd like to go through a loop $FILES times.  Can
>>this be done in sh?

>POSIX states that sh(1) should be able to evaluate expressions, 
>so you can do something like
>while [ $FILES != 0 ]
>do
>	echo -n '* '
>	FILES=$[$FILES - 1]
>done

>But I haven't seen a sh anywhere that is already capable of doing this
>(not even the one I am writing myself for Minix... yet.).
>Maybe somebody knows if a new ksh can do this?

In the version of ksh running on the RS/6000, the following is possible:

typeset -i FILES=10
while [ $i -gt 0 ] ; do
	# body of loop
	FILES=FILES-1
done

or the following:

typeset -i FILES=10
while ((i > 0)) ; do
	# body of loop
	FILES=FILES-1
done

or if you want to be more specific:

typeset -i FILES=10
while ((i > 0)) ; do
	# body of loop
	let FILES=FILES-1
done

The typeset -i forces FILES to be interpreted as an integer and allows
you to forgo the use of $var and the let syntax. let is a shell builtin
which uses (( and )) as shorthand much the same way test uses [ and ].

Rob Tulloh
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