Command chaining (&&, ||, ;) in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run echo Hello only if ls succeeds.

Linux CLI

ls [1] echo Hello

Drag options to blanks, or click blank then click option'

A;

B|

C&&

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using '||' runs the second command only if the first fails.

Using ';' runs commands regardless of success.

Using '|' pipes output, not for conditional chaining.

The '&&' operator runs the second command only if the first command succeeds.

2fill in blank

medium

Complete the code to run echo Failed only if cat file.txt fails.

Linux CLI

cat file.txt [1] echo Failed

Drag options to blanks, or click blank then click option'

A||

B;

C&&

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using '&&' runs the second command only if the first succeeds.

Using ';' runs commands regardless of success.

Using '|' pipes output, not for conditional chaining.

The '||' operator runs the second command only if the first command fails.

3fill in blank

hard

Fix the error in the command to run echo Done after mkdir test regardless of success.

Linux CLI

mkdir test [1] echo Done

Drag options to blanks, or click blank then click option'

A;

B||

C&&

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using '&&' runs second command only on success.

Using '||' runs second command only on failure.

Using '|' pipes output, not for chaining commands.

The ';' operator runs the second command regardless of the first command's success or failure.

4fill in blank

hard

Fill both blanks to run echo Success if grep 'hello' file.txt succeeds, else run echo Fail.

Linux CLI

grep 'hello' file.txt [1] echo Success [2] echo Fail

Drag options to blanks, or click blank then click option'

A&&

B||

C;

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using ';' runs all commands regardless of success.

Using '|' pipes output, not for conditional chaining.

Swapping '&&' and '||' changes logic.

Use '&&' to run 'echo Success' if grep succeeds, and '||' to run 'echo Fail' if grep fails.

5fill in blank

hard

Fill both blanks to run echo Start, then run ls /tmp if echo Start succeeds, else run echo Error.

Linux CLI

; echo Start [1] ls /tmp [2] echo Error

Drag options to blanks, or click blank then click option'

A;

B&&

C||

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using '|' instead of ';' causes piping, not sequencing.

Mixing order of '&&' and '||' changes logic.

Using only ';' runs all commands regardless of success.

Use ';' to run 'echo Start' first, then '&&' to run 'ls /tmp' if 'echo Start' succeeds, and '||' to run 'echo Error' if 'ls /tmp' fails.

Practice

1. What does the command chaining operator && do in Linux shell?

easy

A. Runs the next command only if the previous command succeeded

B. Runs the next command only if the previous command failed

C. Runs all commands regardless of previous command success

D. Runs the next command in the background

Solution

1. Step 1: Understand the meaning of &&

   The && operator runs the next command only if the previous command returns success (exit status 0).

2. Step 2: Compare with other operators

   || runs next command only if previous failed, and ; runs commands regardless of success.

3. Final Answer:

   Runs the next command only if the previous command succeeded -> Option A

4. Quick Check:

   && means run next if success [OK]

Hint: Remember: && means next runs only on success [OK]

Common Mistakes:

• Confusing && with ||
• Thinking && runs commands regardless
• Assuming && runs commands in background

2. Which of the following is the correct syntax to run cmd1 and then cmd2 regardless of cmd1's success or failure?

easy

A. cmd1 && cmd2

B. cmd1 || cmd2

C. cmd1 ; cmd2

D. cmd1 & cmd2

Solution

1. Step 1: Identify the operator that runs commands regardless

   The semicolon ; runs commands one after another no matter if the first succeeds or fails.

2. Step 2: Check other options

   && runs next only if first succeeds, || runs next only if first fails, & runs command in background.

3. Final Answer:

   cmd1 ; cmd2 -> Option C

4. Quick Check:

   ; runs commands regardless [OK]

Hint: Use ; to run commands one after another always [OK]

Common Mistakes:

• Using && or || when unconditional run is needed
• Confusing & (background) with ;
• Missing spaces around operators

3. What will be the output of the following commands if file.txt does not exist?
cat file.txt && echo "File exists" || echo "File missing"

medium

A. File exists

B. File missing

C. No output

D. cat: file.txt: No such file or directory

Solution

1. Step 1: Understand command chaining behavior

   cat file.txt fails because file does not exist, so && echo "File exists" is skipped, and || echo "File missing" runs.

2. Step 2: Predict output

   The error message from cat is printed to stderr (not shown here), but the command output from chaining is File missing.

3. Final Answer:

   File missing -> Option B

4. Quick Check:

   Failed cat triggers || echo [OK]

Hint: Remember: || runs next if previous fails [OK]

Common Mistakes:

• Expecting 'File exists' output
• Ignoring that cat prints error to stderr
• Thinking no output appears

4. Identify the error in this command chaining:
mkdir newdir || echo "Created" && cd newdir

medium

A. The echo message is incorrect

B. mkdir should be followed by ; not ||

C. The chaining logic runs cd only if echo runs

D. No error, command works as intended

Solution

1. Step 1: Analyze the chaining logic

   Operators || and && have equal precedence and associate left-to-right: parsed as (mkdir newdir || echo "Created") && cd newdir.

2. Step 2: Trace execution

   mkdir success: skip echo, success && cd runs. mkdir fail: run echo "Created" (success) && cd runs. Error: echo "Created" runs only on failure (dir exists), wrong message.

3. Final Answer:

   The echo message is incorrect -> Option A

4. Quick Check:

   || echo "Created" runs on mkdir fail [OK]

Hint: || triggers echo only on failure, check message [OK]

Common Mistakes:

• Misparsing as right-associative (mkdir || (echo && cd))
• Thinking cd skips on mkdir success
• Overlooking echo on mkdir failure

5. You want to run backup.sh only if prepare.sh succeeds, but if prepare.sh fails, you want to run cleanup.sh. Which command chaining achieves this?

hard

A. prepare.sh || cleanup.sh && backup.sh

B. prepare.sh && (backup.sh || cleanup.sh)

C. prepare.sh ; backup.sh ; cleanup.sh

D. prepare.sh && backup.sh || cleanup.sh

Solution

1. Step 1: Understand the requirement

   Run backup.sh only if prepare.sh succeeds; if prepare.sh fails, run cleanup.sh.

2. Step 2: Analyze prepare.sh && backup.sh || cleanup.sh

   prepare.sh && backup.sh || cleanup.sh means: if prepare.sh succeeds, run backup.sh. If either prepare.sh or backup.sh fails, run cleanup.sh. This matches the requirement.

3. Final Answer:

   prepare.sh && backup.sh || cleanup.sh -> Option D

4. Quick Check:

   Run backup if prepare succeeds, else cleanup [OK]

Hint: Use && then || to handle success and failure paths [OK]

Common Mistakes:

• Running cleanup even if prepare succeeds
• Running backup even if prepare fails
• Using ; which ignores success/failure