> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Logging
> Track events with ISO 8601 timestamps by wrapping date calls in functions for consistent, machine-friendly logs across environments.
Track events with ISO 8601 timestamps by wrapping `date` calls in functions. This ensures consistent, machine-friendly logs across environments.
## Why Use Timestamped Logs
Timestamped entries help you:
* Debug sequences in real time
* Audit events in containerized workflows
* Reconstruct failures across distributed systems
## Quick Demo: Inline Timestamp
Use `echo` with command substitution to append UTC time:
```bash theme={null}
echo "$(date -u +"%Y-%m-%dT%H:%M:%SZ") : Script event happening"
```
Output:
```text theme={null}
2023-05-20T03:51:03Z : Script event happening
```
## Reusable `log` Function
Instead of repeating timestamp logic, encapsulate it:
```bash theme={null}
#!/usr/bin/env bash
log() {
echo "$(date -u +"%Y-%m-%dT%H:%M:%SZ") ${*}" >&2
}
log "Hello World!"
```
Running `./log.sh` produces:
```text theme={null}
2023-06-01T05:42:45Z Hello World!
```
Sending log messages to standard error (`>&2`) separates them from regular output and integrates better with redirection.
## ISO 8601 Date Format
Using `YYYY-MM-DDThh:mm:ssZ` guarantees consistency across locales. Common `date` specifiers:
| Specifier | Meaning |
| --------- | --------------------- |
| %Y | Year (4 digits) |
| %m | Month (01–12) |
| %d | Day of month (01–31) |
| %H | Hour (00–23) |
| %M | Minute (00–59) |
| %S | Second (00–59) |
| %Z | Time zone (e.g., UTC) |
Test formats:
```bash theme={null}
date
date -u +"%Y-%m-%dT%H:%M:%SZ"
# 2023-05-19T15:53:19Z
```
Avoid over-logging. Too verbose logs can obscure critical information and degrade performance.
## Best Practices
* Write logs for humans: clear, concise, and actionable.
* Include only relevant data: timestamps, event messages, and context.
* Use consistent formatting to facilitate automated parsing.
## Links and References
* [GNU date Manual](https://www.gnu.org/software/coreutils/manual/html_node/date-invocation.html)
* [ISO 8601 Standard Overview](https://en.wikipedia.org/wiki/ISO_8601)
* [Advanced Bash-Scripting Guide](https://tldp.org/LDP/abs/html/)