Question

Do you know how I could use a backreference as a variable name, in sed?

What I tried:

#!/bin/bash
var_one=x
var_two=y
var_three=z
echo "var_one + var_two = var_three" | sed -e "s/\(var_[^\ ]*\)/$\1/g"

What I got:

$var_one + $var_two = $var_three

What I want to get:

x + y = z

Answer 1

Expand Variables with Eval

It’s not clear what you’re really trying to do, but if all you want to do is create some variables in a string, and then evaluate the string to expand the variables, then you want to use eval. For example:

#!/bin/bash
var_one=x
var_two=y
var_three=z
result=$(
    echo "var_one + var_two = var_three" |
    sed -e "s/\(var_[^\ ]*\)/$\1/g"
)
eval "echo $result"

There are a lot of pitfalls involved with using eval. However, this code certainly solves the problem you’ve described.