Generates a log file from latest tag and (n) of commits passed

generate_release_log.sh

#!/bin/bash -
#title          :generate_release_log.sh
#description    :generates a log file from latest tag and (n) of commits passed
#author         :Cristovao Verstraeten
#date           :20160709
#version        :20160709
#usage          :./generate_release_log.sh
#notes          :
#bash_version   :4.3.39(3)-release
#============================================================================
set -euo pipefail
IFS=$'\n\t'

NUMBER=$1

check_argument() {
  if [[ "$NUMBER" =~ ^-[0-9]+$ ]] 2>/dev/null; then
    trap 'rm tempfile' EXIT
    write_release_log
  else
    echo "Usage: ./generate_release_log -[0-9]"
    exit 0
  fi
}

write_release_log() {
  local TAG
  local COMMITS

  TAG=$(git describe --abbrev=0)
  COMMITS=$(git log "$NUMBER" --pretty="%h - %s")

  if [[ ! -f 'release_notes' ]]; then
    touch release-log.txt
  fi

  cat << EOF | tee tempfile
[$TAG]
$COMMITS
EOF

  cat tempfile release-log.txt > tempfile2 && mv tempfile2 release-log.txt
}

# Main
check_argument