Tilde expansion (~) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this command?

Consider the following bash command run by user 'alice' whose home directory is '/home/alice':

echo ~

What will be printed?

Bash Scripting

echo ~

A /root

B ~

C /home

D /home/alice

💡 Hint

The tilde (~) expands to the current user's home directory in bash.

In bash, the tilde (~) alone expands to the home directory of the current user. Since the user is 'alice', it expands to '/home/alice'.

💻 Command Output

intermediate

What does this command output?

Given that user 'bob' exists with home directory '/home/bob', what is the output of:

echo ~bob

when run by user 'alice'?

Bash Scripting

echo ~bob

A /home/bob

B ~bob

C /home/alice

D Error: user not found

💡 Hint

Tilde followed by a username expands to that user's home directory.

In bash, ~username expands to the home directory of that user. Since 'bob' exists with home '/home/bob', it expands accordingly.

📝 Syntax

advanced

Which command correctly uses tilde expansion to list files in the home directory?

You want to list all files in your home directory using tilde expansion. Which of the following commands will work correctly?

A ls '~/'

B ls "~/"

C ls ~/

D ls ~

💡 Hint

Tilde expansion does not occur inside quotes.

Tilde expansion happens only when the tilde is unquoted. Option C uses unquoted ~/, so it expands correctly. Options B and C quote the tilde, so no expansion occurs. Option C works but lists the home directory without trailing slash, which is valid but less explicit.

💻 Command Output

advanced

What is the output of this command?

Assuming user 'carol' has home directory '/home/carol', what is the output of:

echo ~carol/Documents

when run by user 'dave'?

Bash Scripting

echo ~carol/Documents

A /home/carol/Documents

B ~carol/Documents

C Error: user carol not found

D /home/dave/Documents

💡 Hint

Tilde expansion works with usernames followed by paths.

The tilde with username expands to that user's home directory, and the rest of the path is appended. So it becomes '/home/carol/Documents'.

💻 Command Output

expert

What is the output of this script snippet?

Consider this bash script snippet run by user 'eve' whose home directory is '/home/eve':

dir=~
echo "$dir"

What will be printed?

Bash Scripting

dir=~
echo "$dir"

A /home/eve

B ~

C Error: invalid assignment

D $HOME

💡 Hint

Tilde expansion does not happen during variable assignment without evaluation.

When assigning dir=~, the tilde is not expanded because tilde expansion happens only in unquoted command arguments, not in variable assignments. So dir contains the literal '~'.

Practice

1. What does the tilde symbol ~ represent in a bash shell?

easy

A. The current user's home directory

B. The root directory

C. The current working directory

D. A temporary directory

Solution

1. Step 1: Understand tilde usage in bash

   The tilde ~ is a shortcut that expands to the current user's home directory path.

2. Step 2: Compare options with definition

   Only the current user's home directory correctly states that ~ means the current user's home directory.

3. Final Answer:

   The current user's home directory -> Option A

4. Quick Check:

   Tilde (~) = home directory [OK]

Hint: Remember: ~ always means your home folder [OK]

Common Mistakes:

• Confusing ~ with root directory /
• Thinking ~ means current directory
• Assuming ~ is a temporary folder

2. Which of the following is the correct way to refer to another user's home directory named alice using tilde expansion?

easy

A. ~ /alice

B. ~/alice

C. ~ alice

D. ~alice

Solution

1. Step 1: Understand tilde with username

   Using ~username refers to that user's home directory without a slash after the username.

2. Step 2: Check each option

   ~ /alice has a space after ~, invalid. ~/alice refers to alice subfolder in current user's home. ~alice correctly refers to alice's home directory. ~ alice has space between ~ and alice, invalid syntax.

3. Final Answer:

   ~alice -> Option D

4. Quick Check:

   ~username = user's home directory [OK]

Hint: Use ~username without spaces or slashes to get their home [OK]

Common Mistakes:

• Adding a slash immediately after username
• Putting space between ~ and username
• Using ~/username which means subfolder in current user's home

3. What will be the output of the following bash command if the current user's home directory is /home/bob?

echo ~

medium

A. /home/bob

B. ~

C. /root

D. Error: command not found

Solution

1. Step 1: Understand echo with tilde

   The shell expands ~ to the current user's home directory before running echo.

2. Step 2: Apply expansion

   Since the home directory is /home/bob, the command becomes echo /home/bob, which prints /home/bob.

3. Final Answer:

   /home/bob -> Option A

4. Quick Check:

   echo ~ outputs home directory path [OK]

Hint: echo ~ prints your home folder path [OK]

Common Mistakes:

• Expecting echo to print ~ literally
• Confusing with root directory /root
• Thinking echo ~ causes error

4. You wrote this bash command to list files in your home directory:

ls ~

But it shows an error: ls: cannot access '~': No such file or directory. What is the most likely cause?

medium

A. ls command does not support ~

B. You put single quotes around ~, preventing expansion

C. You need to use $HOME instead of ~

D. Your home directory does not exist

Solution

1. Step 1: Understand tilde expansion and quoting

   Tilde expansion happens only when ~ is unquoted. Quoting it (like '~') disables expansion.

2. Step 2: Analyze error cause

   The error shows ls tried to find a folder literally named '~', meaning expansion did not happen due to quotes.

3. Final Answer:

   You put single quotes around ~, preventing expansion -> Option B

4. Quick Check:

   Quotes block tilde expansion [OK]

Hint: Never quote ~ if you want it expanded [OK]

Common Mistakes:

• Assuming ~ always expands even in quotes
• Thinking home directory is missing
• Believing ls cannot use ~

5. You want to write a bash script that copies a file named notes.txt from the home directory of user carol to your current directory. Which command correctly uses tilde expansion to do this?

hard

A. cp ~/carol/notes.txt .

B. cp ~ /carol/notes.txt .

C. cp ~carol/notes.txt .

D. cp ~carol notes.txt .

Solution

1. Step 1: Understand tilde with username and path

   ~carol expands to carol's home directory. Adding /notes.txt accesses the file inside her home.

2. Step 2: Check each option

   cp ~carol/notes.txt . correctly uses ~carol/notes.txt. cp ~/carol/notes.txt . uses ~/carol/notes.txt which means a subfolder carol inside your home, wrong user. cp ~ /carol/notes.txt . has a space breaking the path. cp ~carol notes.txt . misses the slash before filename, so it tries to copy a directory.

3. Final Answer:

   cp ~carol/notes.txt . -> Option C

4. Quick Check:

   ~username/file = file in that user's home [OK]

Hint: Use ~username/path to access files in another user's home [OK]

Common Mistakes:

• Using ~/username which is wrong path
• Adding spaces breaking tilde expansion
• Forgetting slash between username and file