Robust bash scripts do more than automate tasks—they handle errors gracefully, respond to system signals, and support efficient debugging. These practices are essential for reliability and security in production environments.
Error Handling in Bash Scripts
Error handling in Bash scripts allows predictable behavior even when commands fail. The list below demonstrates strict mode, conditional checks, and reliable function practices.
Strict Mode for Safer Scripts
Enable strict error handling at the script’s start:
set -euo pipefail
IFS=$'\n\t'set -e: Exit script immediately on error.
set -u: Treat undefined variables as errors.
set -o pipefail: Treat any failure in pipelines as an error.
Setting IFS safely reduces issues from word splitting.
Checking Exit Status Manually
1. For commands where you want customized error handling:
command
if [ $? -ne 0 ]; then
echo "Command failed" >&2
exit 1
fi2. Use || for concise error action:
mkdir /important/dir || { echo "mkdir failed"; exit 1; }Writing Reliable Functions
1. Return explicit exit codes and check function results.
my_func() {
# ... logic
return 0 # indicate success
}
if ! my_func; then
echo "my_func failed" >&2
fi2. Print error messages to stderr (>&2) so they don’t mix with expected output.
Signal Handling with trap
Signals are notifications (like interrupts) sent to scripts or programs (e.g., SIGINT for Ctrl+C, SIGTERM for termination). Handling signals lets scripts clean up resources, finish gracefully, and avoid leaving files or processes orphaned.
Using trap for Cleanup and Control
The trap command registers handlers for specific signals.
trap 'echo "Interrupted! Exiting safely"; cleanup; exit 1' SIGINT SIGTERMCleanup before exit:
cleanup() {
rm -f "$tmpfile"
}
trap cleanup EXITExample: Ignore Ctrl+C but print a message
trap 'echo "SIGINT received and ignored!"' SIGINTList all trap-able signals:
trap -lDebugging Bash Scripts
Debugging allows developers to understand code execution and catch errors early. The list below demonstrates tracing commands, monitoring variables, static checking, and modular testing practices.
Enable Debug Modes
1. Trace execution with:
set -xPrints each command and its arguments as they execute—disable with set +x.
2. Combines well with selective DEBUG tracing using:
trap 'echo "Executing line $LINENO: $BASH_COMMAND"' DEBUGLogging and Print Statements: Use echo or printf to display variable values and track code flow during development or troubleshooting. For persistent debugging, write outputs to log files to maintain a record of script execution.
Static Analysis Tools: Leverage tools like ShellCheck to detect syntax errors, unsafe practices, and style issues before running scripts. This helps ensure scripts are reliable and adhere to best practices.
Modular Testing: Break scripts into functions and test each independently with sample inputs. Use early returns and explicit error codes within functions to simplify debugging and improve code reliability.
Class Sessions
Sales Campaign
We have a sales campaign on our promoted courses and products. You can purchase 1 products at a discounted price up to 15% discount.