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From: bob@wyse.wyse.com (Bob McGowen x4312 dept208)
Newsgroups: comp.unix.shell
Subject: Re: sh loop variable and "double indirection"
Message-ID: <3110@wyse.wyse.com>
Date: 2 Feb 91 00:35:12 GMT
References: <1991Jan27.044258.18779@shibaya.lonestar.org> <a21801wv11X.00@amdahl.uts.amdahl.com>
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Reply-To: bob@wyse.UUCP (Bob McGowen x4312 dept208)
Organization: Wyse Technology
Lines: 68

In article <a21801wv11X.00@amdahl.uts.amdahl.com> krs@amdahl.uts.amdahl.com (Kris Stephens [Hail Eris!]) writes:
>In article <1991Jan27.044258.18779@shibaya.lonestar.org> 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

deleted ksh stuff

>The sh version is the same except for two parts:  delete the typeset,
>because it's not in sh, and replace   ((j = $j + 1))  with a call
>j=`expr $j + 1`  (which is the extra fork/exec).
>
>>Not very elegant since a limit of 10 iterations is hard-wired.  Can anybody
>>think of a more concise way to do this?  Using PERL is not an option, this
>>must be portable sh code.

deleted second problem


Another solution, involving only one extra fork/exec, is a small C
program to take a command line arg which is the number of iterations
needed and which prints out a character that number of times.  This
would be used in a for loop arg list with backquotes:

  for count in `iter $1`
  do
     process for $1 iterations
  done

I wrote this once but do not have the code to hand, so the following
is from memory and includes no error checking:

   #include <stdio.h>

   main(argc,argv)
   int argc;
   char **argv;
   {
      int count, iterations;

      iterations=atoi(*(argv+1));

      for(count=0; count < iterations; count++)
      {
	 putchar('a');
	 putchar(' ');  /* to separate the characters */
      }
   }

A slightly more complex version was written up in UNIXWorld, Wizard's
Grabbag.  Instead of putting out one character per iteration it
printed the integer with printf, followed by a newline.  I do not
remember the rationale given for using this method.  The mods are
left up to you if you prefer that approach.  I did just compile the
above and it works as advertised.

Note that the for loop variable will not contain anything of value,
it is just a method for looping a specific number of times.

Bob McGowan  (standard disclaimer, these are my own ...)
Product Support, Wyse Technology, San Jose, CA
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