Command chaining (&&, ||, ;) in Linux CLI - Step-by-Step Execution

Concept Flow - Command chaining (&&, ||, ;)

Start

↓

Execute first command

↓

Check exit status

↓

If &&

↓

Execute next command

↓

If first failed?

↓

Skip

↓

End or next chain

This flow shows how the shell runs commands connected by &&, ||, or ; based on success or failure of previous commands.

Execution Sample

Linux CLI

echo Hello && echo World || echo Fail; echo Done

Runs 'echo Hello', then 'echo World' if first succeeds, else 'echo Fail', then always 'echo Done'.

Execution Table

Step	Command	Previous Exit Status	Condition Checked	Action Taken	Output
1	echo Hello	N/A	Run first command	Execute	Hello
2	echo World	0 (success)	&&: previous success?	Execute	World
3	echo Fail	0 (success)	||: previous failed?	Skip
4	echo Done	N/A	;: always run next	Execute	Done

💡 All commands processed; chaining rules determined which commands ran.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
Exit Status	N/A	0	0	0	0
Command Executed	None	echo Hello	echo World	echo World (skip echo Fail)	echo Done

Key Moments - 3 Insights

Why does 'echo Fail' not run even though it is after 'echo World'?

Because 'echo World' succeeded (exit status 0), the '||' operator skips the next command if the previous succeeded, as shown in step 3 of the execution_table.

What is the difference between ';' and '&&' in chaining?

';' always runs the next command regardless of success or failure, while '&&' runs the next command only if the previous succeeded. See step 4 where 'echo Done' runs no matter what.

How does the shell decide to run the second command after '&&'?

It checks if the previous command's exit status is zero (success). If yes, it runs the next command. This is shown in step 2 where 'echo World' runs because 'echo Hello' succeeded.

Visual Quiz - 3 Questions

Look at the execution table, what is the exit status after step 1?

A 0 (success)

B 1 (failure)

C N/A

D Undefined

💡 Hint

Check the 'Previous Exit Status' column for step 2 which shows the exit status after step 1.

At which step does the shell skip a command due to chaining rules?

A Step 2

B Step 4

C Step 3

D No commands are skipped

💡 Hint

Look at the 'Action Taken' column in the execution_table to find where a command is skipped.

If the first command 'echo Hello' failed, which command would run next?

A 'echo Fail' only

B 'echo Fail' and 'echo Done'

C 'echo World' and 'echo Fail'

D 'echo World' only

💡 Hint

Consider how '&&' and '||' behave on failure, referencing the concept_flow and execution_table logic.

Concept Snapshot

Command chaining connects commands with operators:
- '&&' runs next only if previous succeeds
- '||' runs next only if previous fails
- ';' runs next always
Exit status (0=success) controls flow
Use chaining to combine commands smartly

Full Transcript

This lesson shows how Linux shell command chaining works using &&, ||, and ; operators. The shell runs the first command, then checks its exit status. If chained with &&, the next command runs only if the previous succeeded (exit status 0). If chained with ||, the next command runs only if the previous failed (non-zero exit status). The ; operator runs the next command always, regardless of previous success or failure. The example 'echo Hello && echo World || echo Fail; echo Done' runs 'echo Hello' first. Since it succeeds, 'echo World' runs next. Because 'echo World' succeeded, 'echo Fail' is skipped due to ||. Finally, 'echo Done' runs because ; always runs the next command. This chaining lets you control command flow based on success or failure, useful for scripting and command line tasks.