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From: mcgrew@ichthous.Eng.Sun.COM (Darin McGrew)
Newsgroups: comp.unix.shell
Subject: Re: sh loop variable and "double indirection"
Message-ID: <6727@exodus.Eng.Sun.COM>
Date: 28 Jan 91 18:45:22 GMT
References: <1991Jan27.044258.18779@shibaya.lonestar.org>
Sender: news@exodus.Eng.Sun.COM
Organization: Sun Microsystems, Mt. View, Ca.
Lines: 43

afc@shibaya.lonestar.org (Augustine Cano) writes:
>I am trying to specify (at run time) an upper limit for a loop in a shell
>script.  In pseudo-code the ideal would be something like this:
>
>read i
>for 0 to i
>do
>...
>done

I'd use a while loop, as such:

	read max	# Note: there is no sanity check of $max
	counter=0
	while [ $counter -le $max ]
	do
		...
		counter=`expr $counter + 1`
	done

>The next problem is the thorny one.  Some shell variables having been
>previously set up, say:
>
>var0=REAL_VALUE0
>var1=REAL_VALUE1
>var2=REAL_VALUE2
>var3=REAL_VALUE3
>var4=REAL_VALUE4
>
>I want to manipulate variable names inside the above loop such that
>I could display the "REAL VALUEx" based on the current value of $i.

You need to use the eval operator.  The first evaluation will get
the value of $i, and the second one (ie, the one caused by the
eval operator) will use that value as part of the for loop:

	eval echo \$var$i

                 Darin McGrew     "The Beginning will make all things new,
           mcgrew@Eng.Sun.COM      New life belongs to Him.
       Affiliation stated for      He hands us each new moment saying,
identification purposes only.      'My child, begin again....
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