Date: Sat, 9 Apr 2011 17:57:29 +0200 From: Polytropon <freebsd@edvax.de> To: Dino Vliet <dino_vliet@yahoo.com> Cc: freebsd-questions@freebsd.org Subject: Re: shell programming question: help with expr command Message-ID: <20110409175729.357bbb91.freebsd@edvax.de> In-Reply-To: <824253.34690.qm@web113616.mail.gq1.yahoo.com> References: <824253.34690.qm@web113616.mail.gq1.yahoo.com>
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On Sat, 9 Apr 2011 06:31:28 -0700 (PDT), Dino Vliet <dino_vliet@yahoo.com> = wrote: > Hi folks, > I'm having trouble with a little shell script. Can somebody > explain me why I get 3 times "expr: syntax=A0 error" in my > console after I run this little script? >=20 > #! /usr/local/bin/bash > # testscript=20 >=20 > var1=3D"trees.J48" #other value will be rules.Jrip, rules.DecisionTable > len=3D${#var1} > ind=3D`expr index $var1 s` > pos=3D`expr $len - $ind` > out=3D`expr substr $var1 $ind $pos`=20 >=20 > I would expect (and want the following to happen): >=20 > $ind should contain 6 > $pos should contain 3 > $out should contain J48 (other values will have to be Jrip,DecisionTable) >=20 > Can anyone help me with this? The explaination is quite simple: expr doesn't know "index" or "substr"; see "man expr" for details. A polite sidenote: Unless you have a good reason to code in bash-specific manner, do NOT #!/usr/local/bin/bash, as this is NOT portable (if this is one of your goals); use the standard #!/bin/sh instead. Depending on what you have in mind, maybe mentioning the strengths of perl, sed and awk is worth being mentioned. :-) --=20 Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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