This one is to get current Jira sprint number

get-currentJiraSprint.sh

#!/bin/bash

# This one is to be executed once to figure out rapidBoardId
#curl -u kagarlickij:Password  -X GET -H "Content-Type: application/json" 'https://kagarlickij.atlassian.net/rest/greenhopper/1.0/rapidviews/list'

curl -u USER:PASSWORD -X GET -H "Content-Type: application/json" \
'https://JIRA.DOMAIN.NAME/rest/greenhopper/1.0/sprintquery/17?includeFutureSprints=true&includeHistoricSprints=false' \
| /usr/local/bin/jq '.sprints[] | select(.name | contains("PROJECTNAME")) | select(.state == "ACTIVE") | .name' | sed 's/[^0-9]*//g' > currentSprint.txt

echo "Current Sprint number in Jira is $(cat currentSprint.txt)" 

If others would like to use the same thing by vanilla api

html=$(curl -u ${USER_NAME}:${PASSWORD} -X GET -H "Content-Type: application/json" https://${COMPANY}.atlassian.net/rest/agile/1.0/board/${BOARD_NUMBER}/sprint)
SPRINT_NAME=$(echo "${html}" | jq '.values | first(.[] | select(.state=="active")) | .name')
SPRINT_NUMBER=$(echo "${SPRINT_NAME}" | grep -o -E '[0-9]+')