Shell options (set -e, set -x) in Linux CLI - Step-by-Step Execution

Concept Flow - Shell options (set -e, set -x)

Start Script

↓

Set options: set -e, set -x

↓

Execute commands one by one

↓

If set -x: Print each command before running

↓

If command fails and set -e is on: Exit script immediately

↓

End Script or Exit on error

The shell script starts, sets options to print commands and exit on errors, then runs commands step-by-step, stopping if any command fails.

Execution Sample

Linux CLI

set -e
set -x
echo "Start"
false
echo "End"

This script prints commands as they run, stops immediately when a command fails (false), so 'End' is never printed.

Execution Table

Step	Command	Printed (set -x)	Command Result	Action Taken	Output
1	set -e		Success	Enable exit on error
2	set -x		Success	Enable command printing
3	echo "Start"	+ echo "Start"	Success	Prints Start	Start
4	false	+ false	Failure	Exit script immediately due to set -e
5	echo "End"		Not executed	Script exited before this

💡 Script exits at step 4 because 'false' command fails and set -e is enabled

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
set -e	off	on	on	on	on	on
set -x	off	off	on	on	on	on
Script Running	yes	yes	yes	yes	no	no

Key Moments - 2 Insights

Why does the script stop running after the 'false' command?

Because set -e is enabled (see step 1 in execution_table), the script exits immediately when a command fails, which happens at step 4 with 'false'.

Why do we see the commands printed before their output?

Because set -x is enabled at step 2, the shell prints each command before running it, as shown in the 'Printed (set -x)' column in execution_table.

Visual Quiz - 3 Questions

Look at the execution table, what is printed at step 3 before the output?

A false

B Start

C echo "Start"

D set -e

💡 Hint

Check the 'Printed (set -x)' column at step 3 in the execution_table.

At which step does the script stop running due to an error?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look at the 'Action Taken' column where the script exits due to failure.

If we remove 'set -e', what would happen at step 4?

A Script would continue to step 5

B Script would exit immediately

C Commands would not be printed

D Script would print an error and pause

💡 Hint

Refer to the 'set -e' variable state in variable_tracker and its effect on script flow.

Concept Snapshot

Shell options control script behavior:
- set -e: Exit script on any command failure
- set -x: Print each command before executing
Use set -e to catch errors early
Use set -x to debug by seeing commands run
Together they help write safer, easier-to-debug scripts

Full Transcript

This visual trace shows how shell options set -e and set -x affect script execution. The script starts by enabling set -e to exit on errors and set -x to print commands. Each command runs in order: 'echo "Start"' prints 'Start'. Then 'false' runs and fails. Because set -e is on, the script stops immediately and does not run 'echo "End"'. The variable tracker shows set -e and set -x states turning on and the script running status changing to no after failure. Key moments clarify why the script stops on error and why commands print before output. The quiz tests understanding of printed commands, exit step, and effect of removing set -e.