Logging Best Practices

Structured Logging in BASH Scripts¶

Effective logging is critical for debugging, monitoring, and auditing BASH scripts. Structured logging ensures consistency, readability, and scalability. This section covers best practices for implementing timestamps, log levels, and file rotation in your scripts.

1. Use Timestamps for Contextual Logging¶

Timestamps help correlate log entries with system events and simplify troubleshooting. Always include a consistent timestamp format in your logs.

Example:

log_message() {
    local level="$1"
    local message="$2"
    echo "$(date +'%Y-%m-%d %H:%M:%S') [${level}] ${message}"
}

Usage:

log_message "INFO" "Script started"
log_message "ERROR" "Failed to connect to service"

Output:

2023-10-05 14:23:45 [INFO] Script started
2023-10-05 14:23:45 [ERROR] Failed to connect to service

Tip: Use date +'%Y-%m-%d %H:%M:%S' for ISO 8601-compliant timestamps.

2. Implement Log Levels for Prioritization¶

Define log levels (e.g., DEBUG, INFO, WARNING, ERROR, CRITICAL) to categorize the severity of events. This allows filtering and prioritizing logs during analysis.

Example:

log_debug() { log_message "DEBUG" "$@"; }
log_info() { log_message "INFO" "$@"; }
log_error() { log_message "ERROR" "$@"; }

Usage:

log_debug "Debugging variable: $VAR"
log_error "Critical failure: $ERR_MSG"

Tip: Use set -x for debug output in scripts, but avoid relying on it for production logging.

3. Rotate Logs to Prevent Disk Usage¶

Large log files can consume disk space. Use tools like logrotate (systemd-based) or manual rotation with split/gzip to manage log size.

Example: logrotate Configuration
Create /etc/logrotate.d/myscript:

/path/to/script.log {
    daily
    rotate 7
    compress
    missingok
    notifempty
}

Manual Rotation Example:

# Rotate logs by size
split -b 1M /var/log/script.log /var/log/script.log.
gzip /var/log/script.log.*

Tip: Combine rotation with timestamped filenames (e.g., script-$(date +%Y%m%d).log) for easier archiving.

4. Secure and Centralize Log Storage¶

Store logs in a dedicated directory (e.g., /var/log/myscript/) and set appropriate permissions:

mkdir -p /var/log/myscript
chmod 640 /var/log/myscript/*.log
chown root:adm /var/log/myscript

Tip: Use rsyslog or syslog-ng to send logs to a centralized server for monitoring.

5. Use Colorized Output for Debugging¶

Enhance readability during development with ANSI color codes:

log_info() {
    echo -e "\e[34m[INFO] \e[0m${1}" # Blue text
}
log_error() {
    echo -e "\e[31m[ERROR] \e[0m${1}" # Red text
}

Key takeaways¶

Always include timestamps in logs for contextual clarity.
Use standardized log levels to prioritize and filter messages.
Rotate logs regularly to prevent disk exhaustion.
Secure log files with proper permissions and centralized storage.
Leverage colorized output for faster debugging during development.