Exit codes ($?) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the exit code after a successful command?

Consider the following Bash commands run in sequence:

echo "Hello World"
echo $?

What will be the output of the second echo command?

Bash Scripting

echo "Hello World"
echo $?

A 1

B 0

C Hello World

D Command not found

💡 Hint

The exit code $? shows if the last command succeeded or failed. Zero means success.

The first echo command runs successfully and prints "Hello World". The exit code $? after a successful command is 0.

💻 Command Output

intermediate

Exit code after a failing command

What will be the output of this script?

ls /nonexistent_directory
echo $?

Bash Scripting

ls /nonexistent_directory
echo $?

A No such file or directory

B 1

C 2

D 0

💡 Hint

When a command fails, the exit code is non-zero. Different commands may use different codes.

The ls command fails because the directory does not exist. On many systems, ls returns exit code 2 for this error.

📝 Syntax

advanced

Which script correctly checks the exit code?

You want to run a command and then check if it succeeded using its exit code. Which script snippet correctly does this?

A

command
if $? == 0 then
 echo "Success"
fi

B

command
if [ $? -eq 0 ] then
 echo "Success"
fi

C

command
if [$? -eq 0]; then
 echo "Success"
fi

D

command
if [ $? -eq 0 ]; then
echo "Success"
fi

💡 Hint

Remember to have spaces around brackets and use correct syntax for if statements in Bash.

Option D uses correct syntax: spaces around [ and ], the -eq operator, and the then keyword on the same line or next line.

🚀 Application

advanced

What is the exit code after a pipeline?

Consider this pipeline:

grep 'pattern' file.txt | sort
echo $?

What does the exit code represent?

Bash Scripting

grep 'pattern' file.txt | sort
echo $?

A Exit code of the last command in the pipeline (sort)

B Exit code of the first command in the pipeline (grep)

C 0 if both commands succeed, else non-zero

D Sum of exit codes of both commands

💡 Hint

In Bash, $? after a pipeline returns the exit code of the last command by default.

By default, $? returns the exit code of the last command in the pipeline, which is sort here.

🧠 Conceptual

expert

How to get exit codes of all commands in a pipeline?

You run a pipeline of commands in Bash:

cmd1 | cmd2 | cmd3

How can you get the exit codes of all three commands?

A Use the array ${PIPESTATUS[@]} immediately after the pipeline

B Use the command 'exitcodes' after the pipeline

C Use $? three times, once after each command

D Use 'echo $PIPESTATUS' after the pipeline

💡 Hint

Bash stores exit codes of all pipeline commands in a special array variable.

The special array ${PIPESTATUS[@]} holds exit codes of all commands in the last pipeline executed.

Practice

1. What does the exit code 0 usually mean in bash scripting?

easy

A. The command is still running

B. The command failed

C. The command was skipped

D. The command was successful

Solution

1. Step 1: Understand exit codes meaning

   In bash, exit code 0 means success, any other number means failure or error.

2. Step 2: Interpret exit code 0

   Since 0 means success, the command completed without errors.

3. Final Answer:

   The command was successful -> Option D

4. Quick Check:

   Exit code 0 = success [OK]

Hint: Exit code 0 means success, anything else means error [OK]

Common Mistakes:

• Thinking 0 means failure
• Confusing exit code with process ID
• Checking $? too late after command

2. Which of the following is the correct way to check the exit code of the last command in bash?

easy

A. echo $exit_code

B. echo $?

C. echo $lastcode

D. echo $status

Solution

1. Step 1: Recall special variable for exit code

   The special variable $? holds the exit code of the last command.

2. Step 2: Verify correct syntax

   Using echo $? prints the exit code correctly.

3. Final Answer:

   echo $? -> Option B

4. Quick Check:

   Use $? to get last exit code [OK]

Hint: Use $? immediately after command to get exit code [OK]

Common Mistakes:

• Using undefined variables like $exit_code
• Forgetting to check $? right after command
• Using $status which is not standard

3. What will be the output of this script?

ls /nonexistent_dir
 echo $?

medium

A. 2

B. 0

C. No output

D. ls: cannot access '/nonexistent_dir': No such file or directory

Solution

1. Step 1: Understand the command behavior

   The command ls /nonexistent_dir tries to list a folder that does not exist, so it fails.

2. Step 2: Check exit code after failure

   After failure, $? holds a non-zero exit code, 2 for ls missing directories.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Failed command exit code ≠ 0 [OK]

Hint: Failed commands return non-zero exit codes like 2 [OK]

Common Mistakes:

• Assuming output is 0 for failure
• Confusing error message with exit code
• Expecting no output from echo

4. Consider this script snippet:

mkdir test_dir
false
if [ $? -eq 0 ]; then
  echo "Created"
else
  echo "Failed"
fi

What is the problem if the script always prints "Failed" even when the directory is created?

medium

A. mkdir command does not set exit code

B. The syntax of if statement is wrong

C. The $? is checked too late after mkdir

D. echo command overwrites the exit code

Solution

1. Step 1: Understand exit code timing

   The exit code $? must be checked immediately after the command it relates to.

2. Step 2: Identify delay in checking exit code

   If any command runs between mkdir and checking $?, the exit code changes.

3. Final Answer:

   The $? is checked too late after mkdir -> Option C

4. Quick Check:

   Check $? immediately after command [OK]

Hint: Check $? right after command, no commands in between [OK]

Common Mistakes:

• Checking $? after other commands
• Assuming mkdir never fails
• Misunderstanding if syntax

5. You want to run two commands in a script: cmd1 and cmd2. You want to run cmd2 only if cmd1 succeeded (exit code 0). Which is the best way to do this?

hard

A. cmd1 && cmd2

B. cmd1 || cmd2

C. cmd1; if [ $status -eq 0 ]; then cmd2; fi

D. if [ cmd1 ]; then cmd2; fi

Solution

1. Step 1: Understand conditional execution operators

   The operator && runs the second command only if the first succeeds (exit code 0).

2. Step 2: Compare options for best practice

   cmd1 && cmd2 uses cmd1 && cmd2 which is concise and reliable for this purpose.

3. Final Answer:

   cmd1 && cmd2 -> Option A

4. Quick Check:

   Use && to run second command only if first succeeds [OK]

Hint: Use && to run next command only if previous succeeds [OK]

Common Mistakes:

• Using || which runs second if first fails
• Checking $? manually when && is simpler
• Using if with command but less concise