Bash - Expanding a variable into another variable name

Question

Let's say I have these variables:

VAR_A=resultA
VAR_B=resultB
X=A

I want to get the value of VAR_A or VAR_B based on the value of X.

This is working and gives resultA:

VAR="VAR_$X"
RESULT=${!VAR}

My question is, is there a one-liner for this?

Because indirection expansion doesn't seem to work if it is not the wole name of the variable which is expanded. I tried:

RESULT=${!VAR_$X}
RESULT=${!"VAR_$X"}

...and a lot of other combinations, but it always write "bad substitution"...

@CorentinLimier no, I'm sorry, this is not the same question, because the X variable is included into another variable as a string, and indirection expansion doesn't work in that case. That is the whole point of my question! — scandel
– scandel, Commented Jul 15, 2019 at 13:25

Leon S. · Accepted Answer · 2019-07-15 14:51:10Z

4

There doesn't appear to be a shorter way when using the bash 2 notation of ${!var}. For reference, the "new" bash 2 notation is value=${!string_name_var} and the "old" notation would be: eval value=\$$string_name_var.

You could just use the old notation to make it work like you wanted:

eval RESULT=\$"VAR_$X"

Reference: https://www.tldp.org/LDP/abs/html/bashver2.html#BASH2REF

answered Jul 15, 2019 at 14:51

Leon S.

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Comments

wjandrea · Accepted Answer · 2019-07-15 16:39:16Z

1

You'd be better off using an associative array, at least on recent versions of Bash:

declare -A var=(
    [A]=resultA
    [B]=resultB
)
x=A
result="${var[$x]}"
echo "$result"  # -> resultA

answered Jul 15, 2019 at 16:39

wjandrea

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1 Comment

scandel Over a year ago

I know this would be a better option, but I'm in a context where it is not possible (env vars declared in Gitlab-CI - no arrays allowed).

j23 · Accepted Answer · 2019-07-15 15:16:31Z

0

This should work.

RESULT=$(eval echo \$VAR_$X)

The \ in front of the $ makes it be treated literally.

edited Jul 15, 2019 at 15:16

answered Jul 15, 2019 at 13:57

j23

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1 Comment

Shardj Over a year ago

Even shorter eval RESULT=\$VAR_$X

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