topic Re: nested variable access in Operating System - Linux

nested variable access

devhariprasad — Tue, 29 Aug 2006 08:09:54 GMT

I am trying to write a shell script, which will print the 1st or 2nd or 3rd commanline argument values based on the value contained in a variable (say i=1 or 2 or 3 respectively)

i=2
echo \$$i

I tried different options like \$$i, ${$i}, $'$i', $"$i" etc. but nothing is working out.

Please help me do this.

Re: nested variable access

Peter Godron — Tue, 29 Aug 2006 08:23:49 GMT

HI,
have you looked at using shift within a loop ?

"PSEUDO CODE" !
a=0
b=$1
while $a < $b
do
shift
a=a+1
done
echo $1

Re: nested variable access

Jonathan Fife — Tue, 29 Aug 2006 08:24:46 GMT

Hi,

I'd use an array:

set -A args "$@"

echo ${args[$var]}

Re: nested variable access

Peter Godron — Tue, 29 Aug 2006 08:28:29 GMT

Another option:

#!/usr/bin/sh
echo $*| awk -F' ' '{print $$1};'

Re: nested variable access

spex — Tue, 29 Aug 2006 08:46:51 GMT

Hello,

#!/usr/bin/sh
set -A a "${@}"
i=2
echo "${a[${i}]}"
exit

Note that array indexing starts at 0.

PCS

Re: nested variable access

Marvin Strong — Tue, 29 Aug 2006 08:48:55 GMT

all of those will work a case statement would work also.

case $i in
1)
echo $1
;;
2)
echo $2
;;
3)
echo $3
;;
esac

However personally I always use getopts to process commandline argument values.

while getopts a:ishv: opt
do
case ${opt} in
a) VGM=${OPTARG}
;;
i) opt_i=true
;;
s) opt_s=true
;;
v) VG=${OPTARG}
;;
h|*) usage ${0##*/}
;;
esac
done

Re: nested variable access

Sandman! — Tue, 29 Aug 2006 16:22:51 GMT

Put the following code in your script:

#!/bin/sh
i=2
eval echo \$$i

Re: nested variable access

devhariprasad — Tue, 05 Sep 2006 05:26:54 GMT

The replies were highly useful.