Shell Script Development: Best Practices and Useful Examples
Shell scripting remains one of the most efficient ways to automate tasks, tie together system administration routines and build lightweight tooling on Unix/Linux platforms. Whether youre a novice or an experienced sysadmin, adhering to best practices ensures readability, portability, maintainability and security.
1. Script Structure and Shebang
- Use an explicit interpreter: Always begin scripts with a shebang line, for example
#!/usr/bin/env bashto ensure consistent Bash usage. - Header comments: Include metadata such as description, author, date, version and usage examples in a block comment at the top.
- Exit on errors: Add
set -euo pipefailto catch uninitialized variables, failed commands and pipeline errors.
2. Quotations and Variable Safety
Improper quoting leads to word splitting and glob expansion issues. Always:
- Wrap variables in double quotes:
var - Quote command substitutions:
(command) - Avoid legacy backticks prefer
(…)
3. Error Handling and Logging
- Check exit codes with
iforconstructs. - Redirect logs to a file using
gtamp2or more advanced frameworks likelogger. - Implement a centralized
log()function to prepend timestamps and severity levels.
4. Portability and Shell Compatibility
Different environments may have sh, bash, dash or other shells. To maximize portability:
- Test with
shellcheckanddash -n script.sh. - Avoid Bash-specific features if you target plain POSIX sh.
- Use external utilities (awk, sed, grep) judiciously to maintain performance.
5. Security Considerations
- Avoid command injection: Never trust user input—sanitize or validate via patterns.
- Use
chmod 700on scripts storing credentials. - Handle sensitive data: Keep API keys or passwords out of scripts leverage environment variables or secure vaults.
6. Version Control and Collaboration
- Store all scripts in Git repositories with clear commit messages.
- Write
README.mdorUSAGE.txtfor each tool. - Perform peer reviews and leverage
shellcheckin CI pipelines.
7. Testing and Continuous Integration
- Write unit tests with
bats-coreorshunit2. - Integrate tests in GitHub Actions, GitLab CI or Jenkins.
- Use mock commands to simulate external dependencies.
8. Practical Examples
8.1 Backup Script
#!/usr/bin/env bash
set -euo pipefail
SOURCE_DIR=HOME/projects
DEST_DIR=/backup/(date %Y-%m-%d)
mkdir -p DEST_DIR
rsync -avh --delete SOURCE_DIR/ DEST_DIR/
8.2 Service Health Monitor
#!/usr/bin/env bash
set -euo pipefail
check_service() {
local service=1
if systemctl is-active --quiet service then
echo OK: service is running
else
echo FAIL: service is down >2
systemctl restart service
fi
}
for svc in nginx mysql redis do
check_service svc
done
8.3 VPN Connection Manager
If you automate VPN toggling from the CLI, ensure credentials are securely handled. Example integrating with NordVPN:
#!/usr/bin/env bash
set -euo pipefail
action={1:-status}
case action in
connect) nordvpn login nordvpn connect
disconnect) nordvpn disconnect
status) nordvpn status
) echo Usage: 0 {connectdisconnectstatus} exit 1
esac
For other VPN providers you can adapt the CLI commands. For example, ExpressVPN or Private Internet Access.
9. Summary of Common Commands
| Command | Purpose |
|---|---|
set -euo pipefail |
Fail early on errors, undefined variables and pipeline failures |
trap cleanup EXIT |
Define cleanup actions on script exit |
printf %sn quottextquot |
Portable printing over echo |
getopts |
POSIX-style option parsing |
Conclusion
By following structured practices—clear headers, strict error handling, consistent quoting, security awareness and thorough testing—you’ll craft shell scripts that stand the test of time. Automating routine tasks not only saves effort but also reduces human errors. Embrace CI pipelines, shellcheck linting and peer reviews to elevate your shell scripting from throwaway hacks to robust tools.
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