there is an array like this in bash
array_1=(1 2 3 4 5)
array_2=(6 7 8 9 0)
I have another variable that contains 1 or 2 .
array_index=1
So is it possible to create the array name using that variable - like this ?
array_${array_index}[0]
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2In general, when you think about doing this sort of thing, stop and reconsider. I've never seen a time when dynamically generating a variable name make more sense than putting what you would reference as separate variables into a list/array/collection/container. So use more arrays instead - in your case, an array of arrays.Matt Ball– Matt Ball2014-02-11 05:03:12 +00:00Commented Feb 11, 2014 at 5:03
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@MattBall: in principle, I agree. But bash doesn't have arrays of arrays. Or two-dimensional arrays. It does have string-indexed associative arrays, so you can concatenate two keys with a comma or some such between them in order to fake a two-dimensional array, but that might not be an obvious strategy.rici– rici2014-02-11 05:33:21 +00:00Commented Feb 11, 2014 at 5:33
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(Typo: concatenate, in case anyone else is tired enough that it took more than a moment to figure out. Time for me to sack out, clearly.)keshlam– keshlam2014-02-11 05:35:05 +00:00Commented Feb 11, 2014 at 5:35
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@MattBall bash makes you do some crazy things! :)user2731584– user27315842014-02-11 06:01:42 +00:00Commented Feb 11, 2014 at 6:01
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3 Answers
Use variable indirection to read and declare to write:
array_1=(1 2 3 4 5)
array_2=(6 7 8 9 0)
array_index=1
var="array_${array_index}[0]"
echo "The contents of $var is ${!var}"
declare "$var"="Something Else"
echo "Now $var contains ${!var} instead."
This is safer and easier to use correctly than eval.
1 Comment
chepner
declare $var="New Value" is a little more straightforward than using printf in this case.
Problem is to access a particular element you have to do something like ${array[index]}. But you are also wanting to nest a variable in the array part , which bash won't understand when trying to perform the expansion since it expects array to be a variable.
So the only way I can think of doing this would be to force the array expansion to happen later than your variables. e.g.
> array_1=(1 2 3 4 5)
> array_2=(6 7 8 9 0)
> array_index=1
> eval "echo \${array_$array_index[0]}"
1
As n.m. points out in comments, eval is evil, so you should take care when using it.
answered Feb 11, 2014 at 6:14
Reinstate Monica Please
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1 Comment
Reinstate Monica Please
@Agreed in general. But depending on how OP is making the arrays it can be fine, and I don't think there is a good way to get around it here.