Groovy Script

Groovy Key Value pair edit using dynamic

import groovy.json.JsonSlurper
import groovy.json.JsonOutput
import groovy.json.JsonBuilder
def content = '''
{
  "version": "1.0",
  "repos" : [{
    "name": "service-config",
    "source_root": "/service-config",
    "mountpoint": "test",
    "url" : "http://test.example.com",
    "include_branch_name" : "false",
    "branches" : [""],
    "hooks": [{
      "type": "polling",
      "interval": "15"
    }]
  }]
}'''
def cout = new StringBuilder(), cerr = new StringBuilder()
def gitbranch = 'git name-rev --name-only HEAD'.execute()
gitbranch.consumeProcessOutput(cout, cerr)
gitbranch.waitForOrKill(1000)
println "Command Output"
def slurped = new JsonSlurper().parseText(content)
slurped.repos[0].branches = "${cout.toString().trim()}" //array because you have an array in original json
def builder = new JsonBuilder(slurped)
println(builder.toPrettyString())

Command Output
{
    "version": "1.0",
    "repos": [
        {
            "name": "service-config",
            "source_root": "/service-config",
            "mountpoint": "test",
            "url": "http://test.example.com",
            "include_branch_name": "false",
            "branches": "dev-RE-15",
            "hooks": [
                {
                    "type": "polling",
                    "interval": "15"
                }
            ]
        }
    ]
}```