Passing dynamic terraform variables in json using shell script

Question

I am writing a shell script for replacing a keyword in a json file with a dynamic value using shell.

123.json

{
    "Version": "2012-10-17",
    "Statement": [
      {
        "Effect": "Allow",
        "Principal": {
          "AWS": [
            "arn:aws:iam::xxxxxx:role/role1",
            "arn:aws:iam::yyyyyy:role/role2"
          ]
        },
        "Action": "sts:AssumeRole",
        "Condition": {}
      }
    ]
  }

I am getting the values of role1 and role2 as the terraform variables in shell script

shell.sh file has

echo $role1
echo $role2

$ cat 123.json | sed -n '/role1/ s/role1/$role/ p' 
$ cat 123.json | sed -n '/role1/ s/role1/$role/ p'

But the role1 and role2 are not getting updated. Can someone help me out.

I don't get it - do you use a variable called role1, role2 or role? — Arkadiusz Drabczyk
– Arkadiusz Drabczyk, Commented Aug 15, 2021 at 16:31

Arkadiusz Drabczyk · Accepted Answer · 2021-08-16 08:10:32Z

1

Your sed command doesn't work because shell does not expand variables in single quotes. But sed is not a good tool for editing structured format such as JSON - jq is a better choice:

jq --argjson foo "\"$role1\"" '.Statement[].Principal.AWS[0] |= sub("role1$";$foo)' < 123.json
jq --argjson foo "\"$role2\"" '.Statement[].Principal.AWS[1] |= sub("role2$";$foo)' < 123.json

"\"$role2\"" creates a jq variable from shell variables with literal double quotes added at the beginning and at the end.

To save output back to file you need to use external utilities because jq doesn't have -i option that tools such as sed have. You can either use sponge which is a part of moreutils:

$ jq --argjson foo "\"$role1\"" '.Statement[].Principal.AWS[0] |= sub("role1$";$foo)' < 123.json | sponge 123.json
$ jq --argjson foo "\"$role2\"" '.Statement[].Principal.AWS[1] |= sub("role2$";$foo)' < 123.json | sponge 123.json

or manually write to a temporary file and move file in place of 123.json:

$ temp="$(mktemp)"
$ jq --argjson foo "\"$role1\"" '.Statement[].Principal.AWS[0] |= sub("role1$";$foo)' < 123.json  > "$temp"
$ mv "$temp" 123.json
$ temp="$(mktemp)"
$ jq --argjson foo "\"$role2\"" '.Statement[].Principal.AWS[1] |= sub("role2$";$foo)' < 123.json > "$temp"
$ mv "$temp" 123.json

edited Aug 16, 2021 at 8:10

answered Aug 15, 2021 at 19:35

Arkadiusz Drabczyk

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2 Comments

knowledge20 Over a year ago

Can you try explaining what are u doing as part of it. jq --argjson foo "\"$role1\""

knowledge20 Over a year ago

I ran the above command its updating the file but not saving it. Can you pls help.

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