I want to use sed in a script to modify the content of an existing file. I have a line like this…

sed -i '' 's/${scripts}/${newScripts}/' "$packpath"

… which does not do what I thought it would do on my Mac. I would appreciate any help you can give to correct this line.

On my Mac, I have created a script at ~/.zshrc which contains the lines:

if [ -f ~/.bash_aliases ]; then
  . ~/.bash_aliases
fi

I have a script at ~/.bash_aliases which contains a number of aliases and functions to handle common tasks.

I often create small React projects that I want to deploy to GitHub, using the gh-pages Node module. One step in this process is adding two lines to a file called package.json.

For simplicity, let’s say that the package.json file looks like this, before adding any lines.

{
  "name": "react-project",
  "scripts": {
    "dev": "vite",
    "build": "vite build"
  },
  "dependencies": {
    "react": "^18.2.0",
    "react-dom": "^18.2.0"
  }
}

After, it should look like this:

{
  "name": "react-project",
  "scripts": {
    "dev": "vite",
    "build": "vite build",
    "predeploy": "npm run build",
    "deploy" : "gh-pages -d dist"
  },
  "dependencies": {
    "react": "^18.2.0",
    "react-dom": "^18.2.0"
  }
}

The function that I have added to my .bash_aliases currently looks like this:

ghdeploy() {
  package="package.json"
  packpath="$PWD/$package"
  packtext=`cat $packpath`
  
  deploy_it=",\n    "predeploy": "npm run build",\n    "deploy" : "gh-pages -d dist"n  "

  setopt local_options BASH_REMATCH
  regex='"scripts":[^}]+'

  if [[ "$packtext" =~ "$regex"  ]]; then
    scripts=$BASH_REMATCH[1] ## includes final nss

    if [[ "$scripts" =~ ("deploy": "w+") ]]; then
      echo "package.json already contains deploy script"

    else
      chunk=${scripts:0:-3} ## remove final nss
      newScripts="$chunk$deploy_it"
      echo "newScripts: $newScripts"
      sed -i '' 's/${scripts}/${newScripts}/' "$packpath"
    fi

  else
    echo "scripts not found"
  fi
}

The line echo "newScripts... prints out the change that I want to make, but the line sed -i '' ... does not apply those changes to my file.

What is it that I have failed to understand?