gistfile1.txt

#!/bin/sh

if [ -z "$BRANCHES_TO_SKIP" ]; then
  BRANCHES_TO_SKIP=(master develop test)
fi

BRANCH_NAME=$(git symbolic-ref --short HEAD)
BRANCH_NAME="${BRANCH_NAME##*/}"
REGEXP="([A-Z]{3}-[0-9]+)"
if [[ $BRANCH_NAME =~ $REGEXP ]]
then
  ISSUE_NO="${BASH_REMATCH[1]}"
else
  ISSUE_NO=""
fi

BRANCH_EXCLUDED=$(printf "%s\n" "${BRANCHES_TO_SKIP[@]}" | grep -c "^$BRANCH_NAME$")
if [ -n "$BRANCH_NAME" ] && ! [[ $BRANCH_EXCLUDED -eq 1 ]] && ! [[ $BRANCH_IN_COMMIT -ge 1 ]]; then
  sed -i.bak -e "1s/^/[$ISSUE_NO] /" $1
fi