Shell Logging

October 23, 2017

Bash Logging made easy

Ideally we would like the following:

  • log messages sent to syslog
  • stdout and stderr kept separate
  • stdout and stderr message order preserved

1. Logging with functions

#!/bin/bash

readonly SCRIPT_NAME=$(basename $0)

function log() {
  echo "$@"
  logger -p user.notice -t $SCRIPT_NAME "$@"
}

function err() {
  echo "$@" >&2
  logger -p user.error -t $SCRIPT_NAME "$@"
}

log "writing to stdout"
err "writing to stderr"

Design an Expected format

TimeStamp    LogLevel   Message

readonly SCRIPT_NAME=$(basename $0)
readonly SCRIPT_LOG=/tmp/${SCRIPT_NAME}
touch $SCRIPT_LOG

function SCRIPT_ENTRY(){
    time_info=$(date)
    script_name="${SCRIPT_NAME%.*}"
    echo "[${time_info}] [DEBUG]  > $script_name $FUNCNAME" >> $SCRIPT_LOG
}

function SCRIPT_EXIT(){
    time_info=$(date)
    script_name="${SCRIPT_NAME%.*}"
    echo "[${time_info}] [DEBUG]  < $script_name $FUNCNAME" >> $SCRIPT_LOG
}

function INFO(){
    local function_name="${FUNCNAME[1]}"
    local msg="$1"
    time_info=$(date)
    echo "[${time_info}] [INFO]  $msg" >> $SCRIPT_LOG
}

function DEBUG(){
    local function_name="${FUNCNAME[1]}"
    local msg="$1"
    time_info=$(date)
    echo "[${time_info}] [DEBUG]  $msg" >> $SCRIPT_LOG
}

function ERROR(){
    local function_name="${FUNCNAME[1]}"
    local msg="$1"
    time_info=$(date)
    echo "[${time_info}] [ERROR]  $msg" >> $SCRIPT_LOG
}

Ideally we want to keep things simple

What ended the search for simple logging in bash.

NON-POSIX:

    exec 1> >(logger -s -t $(basename $0)) 2>&1