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Date: Tue, 28 Jun 2005 23:17:05 -0400
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Cc: "freebsd-questions@FreeBSD. ORG" <freebsd-questions@freebsd.org>
Subject: Re: Shell script help
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On Tue, 2005-06-28 at 22:52, fbsd_user wrote:
> My sh shell script ability is not that good.
> Have 2 simple coding problems.
> 
> How do I code a statement to subtract one from a field.
> 
> $rulenum = $rulenum - 1
> $rulenum = '$rulenum - 1'
> 
> one='1'
> $rulenum = $rulenum - $one
> $rulenum='$rulenum - $one'
> 
> None of that works. must really be simple.
> 
> I also have this line
> inruleno=`ipfw list | sed -n -e "s/00\([0-9]*\) $inblock/\1/p"`
> 
> This works ok, the search argument  is  s/00\ but that is not good enough
> because the number can be 0 to 65535. The sed -n -e "s/00\([0-9]*\ needs to
> be changed to just return the first word.
> 
> 
> Thanks for any help you can give.
> 
> 
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"man expr" to give the short answer to your first question:

As an example, x=`expr $x + 1`

536 ~ $ x=4
537 ~ $ x=`expr $x + 1`
538 ~ $ echo $

Note the back-quotes to execute a command and return the result, and the
need for spaces between each token in the expr command.