在字符串中扩展bash变量

Question

I am trying to get a variable within a string to expand - its a path:

/path/to/${variable}/here

1. The string originates in a json file.
2. It is subsequently read by jq - at this point I need the expansion to occur.

Here is the json file:

{
    "server_1":{
      "tag": "storage_1",
      "user": "me",
      "sshKey": "/Users/me/.ssh/id_rsa",
      "target_folder": "/Users/me/Desktop/",
      "pubIp": "127.0.0.1",
      "data_folders": [
        "/Users/me/Desktop/POD_INSTALLS/pod_DB/${BUILD_FOLDER}/data/table1/",
        "/Users/me/Desktop/POD_INSTALLS/pod_DB/${BUILD_FOLDER}/data/table2/"
      ]
    }
}

Here is the jq code (now with working code - thanks all):

  writeFolder=$(jq -r --arg bf "${BUILD_FOLDER}" '.server_'${id}'.data_folders[] | sub("\\${BUILD_FOLDER}";$bf)' "${json_path}")
  for folder in $writeFolder
  do
    ssh -q -o ForwardX11=no -i ${sshKey} ${user}@${pubIp} "mkdir -p ${folder}"
  done

Originally - within the expanded $writeFolder variable, the path could be seen but the ${BUILD_FOLDER} variable remained unexpanded as it was taken literally. (when I used set -x I could see it was surrounded by single quotes).

Eventually used accepted solution from peak to make better use of jq.

Answer 1

As pointed out in the comments, you'd be much better off making jq do as much work as possible. But to use jq, you'll need to fix the JSON. Also, it's not clear to me that you need to compute $numberOfDataFolders at all, so in the interests of simplicity, this is what I'd suggest:

#!/bin/bash

json_path=input.json

BUILD_FOLDER=mybuildfolder

jq -r --arg bf "$BUILD_FOLDER" '.data_folders[] | sub("\\${BUILD_FOLDER}";$bf)' "${json_path}" |
  while read -r writeFolder
    do
    echo mkdir -p "${writeFolder}"
  done 

Once the input has been fixed, this produces:

mkdir -p /Users/me/Desktop/POD_INSTALLS/pod_DB/mybuildfolder/data/table1/
mkdir -p /Users/me/Desktop/POD_INSTALLS/pod_DB/mybuildfolder/data/table2/

Notice also that the -r option circumvents the need to use tr .