Git Hook to check the .gitlab-ci.yml file before creating a commit (pre-commit). It sends the file to gitlab ci lint to check it

pre-commit

#!/bin/bash

###########################
# Validate .gitlab-ci.yml #
#    by  Peter Weinert    #
###########################

# Modified version extracted from https://gitlab.lrz.de/snippets/234

GITLAB_URL="https://gitlab.com"
GITLAB_API_LINT="${GITLAB_URL}/api/v4/ci/lint"
GITLAB_WEB_LINT="${GITLAB_URL}/ci/lint"

ANSI_RED="\e[31m"
ANSI_YELLOW="\e[33m"
ANSI_LIGHT="\e[1m"
ANSI_OFF="\e[0m"

# Check if .gitlab-ci.yml is added or modified in index
CI_CHANGED=`git diff-index --name-only HEAD | grep '.gitlab-ci.yml$'`

if [ ! -z "$CI_CHANGED" ]
then
	# checkout from index to a temporary file named $temp_file
	temp_file_assoc=$(git checkout-index --temp -- .gitlab-ci.yml)
	set -f # Disable file name generation (globbing)
	temp_file=($temp_file_assoc)
	set +f 
	temp_file=${temp_file[0]}
	trap "rm -f $temp_file" EXIT INT TERM # Remove file if the program exit receiva a kill or term signal

	# Sanitize: read the whole file in a loop (:a;N;$!ba), see https://stackoverflow.com/questions/1251999/how-can-i-replace-a-newline-n-using-sed
	# and escape special json characters (\ \f \n \r \t / ") with a backslash.
	SANE_CONTENT="$( cat "$temp_file" | sed -e ':a' -e 'N' -e '$!ba' -e 's/\\/\\\\/g' -e 's/\f/\\f/g' -e 's/\n/\\n/g' -e 's/\r/\\r/g' -e 's/\t/\\t/g' -e 's/\//\\\//g' -e 's/"/\\"/g' )"
	# Pack YAML in JSON
	JSON="{\"content\": \"${SANE_CONTENT}\"}"
	
	# Use Lint - if timeout is reached the validation will succeed nevertheless
	ANSWER=`curl -s --connect-timeout 2 --max-time 4 --header "Content-Type: application/json" ${GITLAB_API_LINT} --data "$JSON"`
	
	ERROR_CODE=$?
	if [[ "$ERROR_CODE" != "0" ]]; then
		echo -e "${ANSI_LIGHT}${ANSI_YELLOW}WARNING: .gitlab-ci.yml not validated!${ANSI_OFF} Curl failed with error code ${ANSI_LIGHT}${ANSI_RED}${ERROR_CODE}${ANSI_OFF}" >&2
	else
		if [[ $ANSWER =~ "invalid" ]]; then
			echo -e "${ANSI_LIGHT}${ANSI_RED}ERROR: Invalid .gitlab-ci.yml.${ANSI_OFF} Lint reports ${ANSWER}." >&2
			echo -e "Use your Gitlab Lint (${GITLAB_WEB_LINT}) for more information." >&2
			echo -e "Aborting commit." >&2
			exit 1
		elif [[ ! $ANSWER =~ "valid" ]]; then
			echo -e "${ANSI_LIGHT}${ANSI_YELLOW}WARNING: No regular answer received.${ANSI_OFF} Lint reports '${ANSWER}'." >&2
			echo -e "This is most likely a bug in the JSON to YAML converter section of this script." >&2
			echo -e "Please report includung the exact .gitlab-ci.yml." >&2
			echo -e "Data send was (backslashes escaped) $( echo "$JSON" | sed -e 's/\\/\\\\/g' )" >&2
#		else
#			echo -e "File .gitlab-ci.yml is valid."
		fi
	fi
fi

It will only generate an output in case of an error arises. Uncomment lines 55 and 56 to get feedback when it passes the validation.