variable variables in BASH

Question

I would like to ask some help regarding variable variables in bash. I've read a few articles about it, but in my case I don't know how to do it. Let see my problem:

The array contains other arrays' names and I want to print the values of these arrays. In inner for I need variable variables.

#!/bin/bash
declare -a array=(dir1 dir2 dir3)
declare -a dir1=(1 2 3)
declare -a dir2=(a b c)
declare -a dir3=(9 8 7)

for elem1 in "${array[@]}"
do
  for elem2 in "${variableVariable[@]}"
  do
    echo "$elem1 : $elem2"
  done
done

The output should be something like this

dir1 : 1
dir1 : 2
dir1 : 3
dir2 : a
dir2 : b
dir2 : c
dir3 : 9
dir3 : 8
dir3 : 7

Don't use variable variables in this case. Use [associative arrays](http://stackoverflow.com/questions/1494178/how-to-define-hash-tables-in-bash). — Alex, May 02 '13 at 05:52
possible duplicate of [Lookup shell variables by name, indirectly](http://stackoverflow.com/questions/1694196/lookup-shell-variables-by-name-indirectly) — tripleee, May 02 '13 at 06:01
@tripleee It's similar to that question, but there's some extra work you have to do to deal with `[@]` when indirecting. It took me a while to figure it out. — Barmar, May 02 '13 at 07:34
Mine problem is the how to deal with `[@]` part of the script. Can you help me? — AndrasCsanyi, May 03 '13 at 18:02

score 7 · Answer 1 · answered May 02 '13 at 05:58

7

This can be done using bash's indirect variable feature.

for elem1 in "${array[@]}"
do
  elems=$elem1'[@]'
  for elem2 in "${!elems}"
  do
    echo "$elem1 : $elem2"
  done
done

Note that this is a bash extension, it's not portable to other shells.

answered May 02 '13 at 05:58

Barmar

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I'll take a look at it. I would like to run my script in git shell on windows. – AndrasCsanyi May 02 '13 at 07:27

AndrasCsanyi · Answer 2 · 2013-05-06T07:37:14.213

0

Finally, I found the solution. I had to use eval because I was not able to deal with the other syntax, I mean the composition of the ${!variable} and the ${variable[@]}.

#!/bin/bash
declare -a array=(dir1 dir2 dir3)
declare -a dir1=(1 2 3)
declare -a dir2=(a b c)
declare -a dir3=(9 8 7)

for elem1 in "${array[@]}"
do
  for elem2 in `eval echo \$\{$elem1\[@\]\}"`
  do
    echo "$elem1 : $elem2"
  done
done

edited May 06 '13 at 07:37

answered May 05 '13 at 12:42

AndrasCsanyi

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variable variables in BASH

2 Answers2