[SOLVED] How to replace a JSON value with variable using sed, but without forward slash delimiter?

Issue

I'm attempting to use the linux command sed to dynamically replace the value of the "branch" property. But, here is the kicker.. I'm using a bash environment variable as the value.

The environment variable:

export BRANCH_NAME=release/feature-branch

Here is my json:

{
 "settings": {
   "repo": "myrepo/my-service",
   "branch": "feature/addition-1"
 }
}

How do I use sed to transform the JSON into:

{
 "settings": {
   "repo": "myrepo/my-service",
   "branch": "release/feature-branch"
 }
}

What I've Tried so far

I have tried this other example from stackoverflow with several variations, but was unsuccessful with this:

sed -i '/branch/c\   \"branch\" : "${BRANCH_NAME}"' settings.json

The result was:

{
 "settings": {
   "repo": "myrepo/my-service",
   "branch": "${BRANCH_NAME}"
 }
}

Solution

Your best option is to use something that knows how to read and write JSON syntax. The canonical tool is jq. Assuming that we have set the shell variable $BRANCH_NAME, we do something like this:

$ jq --arg branch_name "$BRANCH_NAME" \
  '.settings.branch = $branch_name' settings.json
{
  "settings": {
    "repo": "myrepo/my-service",
    "branch": "release/feature-branch"
  }
}

---

The problem with this sed command:

sed -i '/branch/c\   \"branch\" : "${BRANCH_NAME}"' settings.json

is that single quotes (') inhibit variable expansion. You could do this instead:

sed -i '/branch/c\   \"branch\" : "'"${BRANCH_NAME}"'"' settings.json

Notice the somewhat complex quoting going on there; we have effectively:

'...something in single quotes'...something outside single quotes...'something inside single quotes...'

More specifically:

• '/branch/c\ \"branch\" : "'
• "${BRANCH_NAME}"
• '"'

This way, the expression "${BRANCH_NAME}" is outside of the single quotes and is expanded by the shell.

Demo:

$ sed  '/branch/c\   \"branch\" : "'"${BRANCH_NAME}"'"' settings.json
{
 "settings": {
   "repo": "myrepo/my-service",
   "branch": "release/feature-branch"
 }
}

Answered By - larsks

Answer Checked By - Pedro (WPSolving Volunteer)