Essential Bash Scripting Tips for Building Reliable Shell Scripts

0. Enable strict mode with set -xeuo pipefail

Place this command right after the shebang to make Bash abort on errors, treat undefined variables as fatal, and reveal hidden issues. The flags mean:

-x : echo each command after variable expansion (useful for debugging).

-e : exit immediately when any command returns a non‑zero status.

-u : treat use of undefined variables as an error.

-o pipefail : cause a pipeline to fail if any component fails.

When you need to ignore a specific failure, append || true or capture the status with || RET=$?.

1. Prevent concurrent executions

When a script is scheduled (e.g., via cron), ensure only one instance runs at a time using flock for file‑based locking.

Method 1 – external wrapper:

flock --wait 5 -e "lock_myscript" -c "bash myscript.sh"

Method 2 – inside the script:

exec 123<>lock_myscript
flock --wait 5 123 || { echo 'cannot get lock, exit'; exit 1; }

2. Kill all child processes on unexpected exit

Use a trap to terminate the entire process group when the script receives SIGINT, SIGTERM, or exits:

trap "trap - SIGTERM && kill -- -$$" SIGINT SIGTERM EXIT

Note: This does not work if the parent is killed with SIGKILL (signal 9).

3. Limit execution time with timeout

Wrap a command with timeout to enforce a maximum runtime. The command returns 0 if it finishes in time, otherwise a non‑zero code. timeout 600s some_command arg1 arg2 You can change the signal sent on timeout with -s.

4. Debug long pipelines by persisting intermediate results

Instead of chaining many commands directly, write each stage’s output to a temporary file, then feed the next stage. This aids troubleshooting but may be slower.

cmd1 > out1.dat
cat out1 | cmd2 > out2.dat
cat out2 | cmd3 > out3.dat

For better performance while still keeping intermediate data, use tee:

cmd1 | tee out1.dat | cmd2 | tee out2.dat | cmd3 > out3.dat