Bash Conditions If Else¶
Introduction¶
This Bash guide covers bash conditions if else with scripts that can be tested on a normal Linux host. The examples use safe defaults, quoted variables, and explicit error handling.
Basic Syntax¶
name="server1"
printf "host=%s\n" "$name"
The shell expands variables, runs commands, and uses exit codes to decide whether a step succeeded.
Practical Examples¶
#!/usr/bin/env bash
set -euo pipefail
path="/var/log"
if [[ -d "$path" ]]; then
du -sh "$path"
fi
Real-World Script Example¶
#!/usr/bin/env bash
set -euo pipefail
target="${1:-/tmp}"
if [[ ! -e "$target" ]]; then
echo "target does not exist: $target" >&2
exit 1
fi
printf "checking %s\n" "$target"
ls -ld "$target"
Error Handling¶
if ! systemctl is-active --quiet sshd; then
echo "sshd is not running" >&2
exit 1
fi
Use clear messages and non-zero exits so cron, CI jobs, and monitoring tools can detect failure.
Testing the Script¶
bash -n script.sh
chmod +x script.sh
./script.sh /var/log
echo $?
Expected output:
checking /var/log
drwxr-xr-x. 12 root root 4096 May 30 09:55 /var/log
0
Common Mistakes¶
- Making several changes at once, which hides the real cause.
- Skipping logs or verification commands after a change.
- Assuming the problem is fixed because one command returned successfully.
Best Practices¶
- Use strict mode for administrative scripts.
- Print useful errors to standard error.
- Keep scripts idempotent when they change system state.
- Validate inputs before running privileged commands.
Related Guides¶
Summary¶
Good Bash scripts are predictable: validate input, quote variables, handle errors, and test realistic failure cases before using them in automation.