Simple bash logger

logger.sh

# -------------------------------------------------------------------
# log: simple logger with timestamp, log levels, and color support
#
# Usage:
#   log "message"
#   log INFO "message"
#   log WARN "message with \nnewlines"
#   log ERROR "something went wrong"
#   log DEBUG "debug info"
#
# Pipe command output:
#   some_command |& log
#   some_command |& log WARN
#
# Notes:
# - Timestamps are bold.
# - Log levels: INFO (green), WARN (yellow), ERROR (red), DEBUG (cyan).
# - Colors auto-disable if stdout isn't a TTY or if $NO_COLOR is set.
# - With pipes: prints one timestamp+level header, then passes through output.
# -------------------------------------------------------------------

log() {
  # level is optional first arg: INFO|WARN|ERROR|DEBUG
  local level="INFO"
  case "$1" in INFO|WARN|ERROR|DEBUG) level="$1"; shift;; esac

  # bold timestamp
  local ts="\e[1m$(date '+%Y-%m-%d %H:%M:%S')\e[0m"

  # color (only if stdout is a terminal and NO_COLOR isn't set)
  local cs="" ce=""
  if [ -t 1 ] && [ -z "${NO_COLOR:-}" ]; then
    case "$level" in
      INFO)  cs="\e[32m" ;;  # green
      WARN)  cs="\e[33m" ;;  # yellow
      ERROR) cs="\e[31m" ;;  # red
      DEBUG) cs="\e[36m" ;;  # cyan
    esac
    ce="\e[0m"
  fi

  if [ $# -gt 0 ]; then
    # args path: interpret escapes like \n
    printf "[%b] [%b%b%b] %b\n" "$ts" "$cs" "$level" "$ce" "$*"
  else
    # pipe path: print header once, then pass stdin through
    printf "[%b] [%b%b%b] " "$ts" "$cs" "$level" "$ce"
    cat
  fi
}