Iterate over a file called branches (that should contain a list of branches to be built, one in each line) and triggers another Jenkins job via the REST API and authenticating with the API Token. It pulls the missing revisions from ALL branches as a final step.

JobForEachBranch

for branch in $(cat branches)
do
  echo "---------------"
  echo "Branch: $branch"
  json="{\"parameter\": [{\"name\": \"branch\", \"value\": \"$branch\"}]}"
  curl -F json="$json" -u $1:$2 $JENKINS_URL/job/$2/build?token=$4
done
hg pull -u

Invocation:

JobForEachBranch.sh jenkinsUsername jenkinsAPIToken targetJob targetJobToken