Bash: Store variables in string to get resolved at a later time

Question

This is a small part of the code. I am creating test_args having a variable, which needs to be resolved at a later time, when that variable is defined in that scope, here, inside a for loop.

test_args=""
test_args+='-test.coverprofile=/tmp/coverage${ii}.out'
test_dirs="a b"

ii=0
for d in ${test_dirs[@]}; do
    echo ${test_args}               # actually used as `go test ${test_args}`
    ii=$((ii+1))
done

Current output:

-test.coverprofile=/tmp/coverage${ii}.out
-test.coverprofile=/tmp/coverage${ii}.out

Expected output:

-test.coverprofile=/tmp/coverage0.out
-test.coverprofile=/tmp/coverage1.out

I am open to suggestions for better methods. I need all the files to be created with a different name, so as to prevent overwriting in the loop.

Answer 1

Using eval is the usual solution:

#!/bin/bash

test_args=""
test_args+='-test.coverprofile=/tmp/coverage${ii}.out'
test_dirs="a b"

ii=0
for d in ${test_dirs[@]}; do
    eval echo ${test_args}
    ii=$((ii+1))
done

Which results in:

[user@linux ~]$ ./test2.sh
-test.coverprofile=/tmp/coverage0.out
-test.coverprofile=/tmp/coverage1.out

But here's a useful discussion about this topic - I advise reading the question linked on the left and it's answer, although it doesn't quite fully apply to this use case.