Script Logging

Introduction

When you write a Bash script that runs in the background (like a cron job), you won't be sitting at the terminal to read the echo output. Implementing proper logging inside your scripts is essential to know if a background task succeeded or failed.

Basic Redirection

The simplest way to log is to redirect the execution of the entire script when you call it.

# Run the script, sending stdout and stderr to a log file
./my_script.sh &> /var/log/my_script.log

Custom Logging Functions

For more robust scripts, you should define a custom logging function. This allows you to add timestamps and log levels (INFO, WARN, ERROR) dynamically.

#!/bin/bash

LOG_FILE="/var/log/my_app_deployment.log"

log() {
    local level=$1
    local message=$2
    # The 'date' command formats the timestamp
    local timestamp=$(date +"%Y-%m-%d %H:%M:%S")
    
    # Print to the terminal
    echo "[\${timestamp}] [\${level}] \${message}"
    
    # Append to the log file
    echo "[\${timestamp}] [\${level}] \${message}" >> "\${LOG_FILE}"
}

log "INFO" "Starting the deployment process..."
log "WARN" "Disk space is running low."

Using logger for Syslog

If you want your script's logs to integrate perfectly with the Linux system's built-in logging daemon (Syslog or Journald), use the logger command.

# This sends the message directly to /var/log/syslog (or journalctl)
logger -p user.err "My custom script encountered a critical failure!"

Using logger is highly recommended for enterprise environments, as those system logs are usually automatically forwarded to Datadog or Splunk via an external logging agent.

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