Get variable name while iterating over array in bash

Question

What I have is an array with some variables. I can iterate to get the values of those vars but what I need is actually their names (values will be used elsewhere).

Going with var[i] won't work cause I will have different names. I guess I could workaround this by creating another array with the names - something similar to this: Getting variable values from variable names listed in array in Bash

But I'm wondering if there is a better way to do this.

var1=$'1'
var2=$'2'
var3=$'3'

Array=( $var1 $var2 $var3)

for ((i=0; i<${#Array[@]}; i++))
do
  echo ${Array[i]}
done

Is:

>1
>2
>3

Should be:

>var1
>var2
>var3

Why don't you just store the strings var1 var2 var3 in your array? — Tom Fenech
– Tom Fenech, Commented May 11, 2018 at 14:58
var1=1; var2=2; var3=3; Array=( $var2 $var2 $var3 ) results in Array=( 1 2 3 ). The entries aren't linked to variables in any significant way -- if you then afterwards ran var1=4; var2=5; var3=6, the array would still be 1 2 3; as such, there isn't any metadata to retrieve. — Charles Duffy
– Charles Duffy, Commented May 11, 2018 at 15:01
(and $'1' is exactly the same as 1; there's no point whatsoever to using the alternate literal syntax here -- in most of the cases where there was a point to using that syntax, you'd need to make it Array=( "$var1" "$var2" "$var3" ) to avoid munging your data during the assignment). — Charles Duffy
– Charles Duffy, Commented May 11, 2018 at 15:02
BTW, a language that did allow what you're asking for would be exceedingly rare. In Python, for example, if you set var1=1; var2=2; var3=3; Array=[ var1, var2, var3 ], you can't get back from Array[0]'s value of 1 to the variable var1 it was originally taken from (especially since var1 may no longer have the value 1 at the future point in time when the inspection is desired). — Charles Duffy
– Charles Duffy, Commented May 11, 2018 at 15:26

Charles Duffy · Accepted Answer · 2018-05-11 15:21:16Z

4

It sounds like you want an associative array.

# to set values over time
declare -A Array=( ) || { echo "ERROR: Need bash 4.0 or newer" >&2; exit 1; }
Array[var1]=1
Array[var2]=2
Array[var3]=3

This can also be assigned at once:

# or as just one assignment
declare -A Array=( [var1]=1 [var2]=2 [var3]=3 )

Either way, one can iterate over the keys with "${!Array[@]}", and retrieve the value for a key with ${Array[key]}:

for var in "${!Array[@]}"; do
  val="${Array[$var]}"
  echo "$var -> $val"
done

...will, after either of the assignments up top, properly emit:

var1 -> 1
var2 -> 2
var3 -> 3

edited May 11, 2018 at 15:21

answered May 11, 2018 at 15:05

Charles Duffy

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Comments

ErikMD · Accepted Answer · 2018-05-11 15:29:57Z

1

What about this solution?

#!/bin/bash

var1=$'1'
var2=$'2'
var3=$'3'

Array=( var1 var2 var3 )

for var in "${Array[@]}"; do
  echo "$var = ${!var}"
done

The idea just consists in putting your variable names in the array, then relying on the indirection feature of Bash.

But as pointed out by @CharlesDuffy, the use of associative arrays sounds better adapted to the OP's use case.

Also, this related article may be worth reading: How can I use variable variables… or associative arrays?

edited May 11, 2018 at 15:29

answered May 11, 2018 at 14:59

ErikMD

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1 Comment

Charles Duffy Over a year ago

The OP's question links to stackoverflow.com/questions/29307073/… showing exactly this technique, so I believe they're already familiar with it.

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