DEVOPS: Automatically updating job parameter in Jenkins

This post would ideally follow up after a discussion on configuring Jenkins jobs with Sprint number as a parameter to build jobs. At the start of every sprint, that Sprint number needs to be updated to new sprint. While I'll save the philosophy on that for a later discussion, here's whats here

Problem Statement:
A Jenkins job parameter needs to be updated every 'x' days. This needs to be done for 'n' jobs. A default way is to do it manually, an obviously error-prone way of doing it, where we run the risk of making a wrong update, as well as miss one of the 'n' jobs. In the following config XML of a Jenkins job, the Sprint number needs to be incremented as part of this job

<hudson.model.StringParameterDefinition>
    <name>SPRINT</name>
    <description></description>
    <defaultValue>10</defaultValue>
</hudson.model.StringParameterDefinition>

Resolution:
In true spirit of automation, this task can be automated by creating a Jenkins job that looks at these jobs and updates each of them. Here is a sample shell script (hey, Jenkins is running on Unix, right ;), and can be easily customized for powershell script.

#!/bin/bash
# This job uses Jenkins REST API to fetch job config, invokes python to increment SPRINT
#   and again uses Jenkins REST API to publish updated job config
# It defines an array of jobs that needs to be updated
# It defines a python script that will update job configurations
# It defines a shell function that will compile python function and pass jenkins config, and execute it
# The updated config is POST'ed back to Jenkins


JOB_NAMES=(first-build-job second-build-job third-build-job)
# Step 1: assign python code to increment Sprint value to a shell variable
_increment_sprint_script=$(cat <<'EOF'
import sys, xml.etree.ElementTree as ET
doc = ET.fromstring(sys.stdin.read())
for node in doc.findall('.//hudson.model.StringParameterDefinition'):
    name_el = node.find('./name')
    if name_el is not None and name_el.text == 'SPRINT':
        default_el = node.find('./defaultValue')
        if default_el is None: continue
        default_el.text = str(int(default_el.text) + 1)
print ET.tostring(doc)
EOF
)


# Step 2: define a function that calls the interpreter with that code
increment_sprint() { python -c "$_increment_sprint_script" "$@"; }


# Step 3: Iterate over all jobs and update them
for JOB_NAME in "${JOB_NAMES[@]}"
do
  echo "Updating $JOB_NAME ..."
  updated_config=$(curl "$JENKINS_URL/job/$JOB_NAME/config.xml" | increment_sprint)
  curl -v -X POST --data-binary "$updated_config" -H 'Content-Type: application/xml' -u "$USERID:$TOKEN" "$JENKINS_URL/job/$JOB_NAME/config.xml";
done

The finer details:
1. Notice the quotations in curl commands - pretty important, miss these, and the Jenkins configuration of x-build-job will turn into a single line xml, blotching its script.
2. Its easy to get the configuration wrong by a simpler script that just looks for value of "defaultValue" of current Sprint. While this may usually work, it can fail if there are multiple parameters with same defaultValue as current Sprint