which and whereis for commands in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of which command

What is the output of the command which ls on a typical Linux system?

Linux CLI

which ls

A /bin/ls

B ls: command not found

C /usr/bin/which

D /usr/local/bin/ls

💡 Hint

The which command shows the full path of the executable that runs when you type a command.

The which command searches your PATH and shows the location of the executable. Usually, ls is in /bin.

💻 Command Output

intermediate

Output of whereis command

What does the command whereis python3 typically output?

Linux CLI

whereis python3

A python3: command not found

B python3: /usr/bin/python3 /usr/lib/python3 /usr/share/man/man1/python3.1.gz

C /bin/python3

D /usr/local/bin/python3

💡 Hint

The whereis command shows locations of the binary, source, and manual files.

The whereis command searches standard locations for binaries, source code, and man pages related to the command.

🧠 Conceptual

advanced

Difference between which and whereis

Which statement correctly describes the difference between which and whereis commands?

A <code>which</code> shows source code location; <code>whereis</code> shows only the executable path.

B <code>which</code> searches all system directories; <code>whereis</code> only searches the current directory.

C <code>which</code> shows the path of the executable found in PATH; <code>whereis</code> shows locations of binary, source, and man files.

D <code>which</code> and <code>whereis</code> are identical and interchangeable.

💡 Hint

Think about what each command searches for and where.

which finds the executable in your PATH. whereis looks for binaries, source files, and manual pages in standard system locations.

🔧 Debug

advanced

Why does which fail to find a command?

You run which myscript but get no output, even though myscript runs fine when you type it. Why?

A The script is not in any directory listed in the PATH environment variable.

B The script has no execute permission.

C The which command is broken and needs reinstalling.

D The script is a shell alias or function, not an executable file.

💡 Hint

Think about what which can find and what it cannot.

which only finds executables in PATH. It does not find shell aliases or functions, which can run but are not files.

🚀 Application

expert

Using which and whereis in a script

You want a script to check if the git command is installed and print its path. Which snippet correctly does this?

A if which git > /dev/null; then echo "Git found"; else echo "Git not found"; fi

B if path=$(which git); then echo "Git found at $path"; else echo "Git not found"; fi

C if [ $(which git) ]; then echo "Git found"; else echo "Git not found"; fi

D if whereis git; then echo "Git found"; else echo "Git not found"; fi

💡 Hint

Think about how to check command success and suppress output.

Option A correctly uses which git and checks its exit status, suppressing output. This is the best way to test if git is installed.

Practice

1. What does the which command do in Linux?

easy

A. Lists all files related to a command including source and man pages

B. Displays the manual pages of a command

C. Shows the full path of the executable that runs when you type a command

D. Shows the current directory contents

Solution

1. Step 1: Understand the purpose of which

   The which command searches your PATH environment to find the executable file that runs when you enter a command.

2. Step 2: Compare with other options

   whereis lists multiple locations including source and man files, not just the executable path. Manual pages are shown by man. Directory contents are shown by ls.

3. Final Answer:

   Shows the full path of the executable that runs when you type a command -> Option C

4. Quick Check:

   which = executable path [OK]

Hint: Remember: which = executable path only [OK]

Common Mistakes:

• Confusing which with whereis
• Thinking which shows manual pages
• Assuming which lists all related files

2. Which of the following is the correct syntax to find the location of the ls command using which?

easy

A. which -l ls

B. which ls

C. which --all ls

D. which ls -a

Solution

1. Step 1: Recall basic which syntax

   The basic syntax to find the path of a command is simply which command_name. No extra flags are needed for a single path.

2. Step 2: Analyze options

   Options like -l or --all are not standard or needed for basic usage. Adding -a or extra flags incorrectly after the command name is invalid.

3. Final Answer:

   which ls -> Option B

4. Quick Check:

   Simple syntax: which + command [OK]

Hint: Use just 'which command' to find executable path [OK]

Common Mistakes:

• Adding unnecessary flags to which
• Placing flags after command name
• Using incorrect or unsupported options

3. What will be the output of the command whereis bash on a typical Linux system?

medium

A. bash: /bin/bash /usr/share/man/man1/bash.1.gz

B. bash: command not found

C. /usr/bin/bash

D. /bin/bash

Solution

1. Step 1: Understand whereis output format

   whereis shows multiple locations: the binary executable path, source files if any, and manual page locations.

2. Step 2: Analyze typical output for bash

   On most systems, whereis bash returns the binary path like /bin/bash and the man page location like /usr/share/man/man1/bash.1.gz.

3. Final Answer:

   bash: /bin/bash /usr/share/man/man1/bash.1.gz -> Option A

4. Quick Check:

   whereis = binary + man files [OK]

Hint: whereis shows binary and man page locations [OK]

Common Mistakes:

• Expecting only one path from whereis
• Confusing whereis output with which output
• Thinking whereis returns error if command exists

4. You run which python3 but get no output. What is the most likely reason?

medium

A. Python3 is installed but hidden by a firewall

B. You typed the command incorrectly

C. which command is broken on your system

D. Python3 is not installed or not in your PATH

Solution

1. Step 1: Interpret empty output from which

   If which returns nothing, it means it did not find the executable in any directory listed in your PATH environment variable.

2. Step 2: Consider common causes

   Most often, this means the program is not installed or its executable directory is not in PATH. Typing errors usually cause an error message, not empty output. The command itself rarely breaks, and firewalls do not hide executables.

3. Final Answer:

   Python3 is not installed or not in your PATH -> Option D

4. Quick Check:

   No output from which = command missing or PATH issue [OK]

Hint: No output means command not found in PATH [OK]

Common Mistakes:

• Assuming which is broken
• Blaming firewall for missing executable
• Ignoring PATH environment variable

5. You want to find all locations related to the gcc compiler including binary, source, and manual files. Which command should you use?

hard

A. whereis gcc

B. which gcc

C. locate gcc

D. find / -name gcc

Solution

1. Step 1: Understand the purpose of each command

   which shows only the executable path. locate searches a database for filenames but may show unrelated files. find searches the entire filesystem but is slow and may produce too many results.

2. Step 2: Identify the command that shows binary, source, and manual files

   whereis is designed to show all related locations for a command including binary, source, and man pages, making it the best choice.

3. Final Answer:

   whereis gcc -> Option A

4. Quick Check:

   whereis = binary + source + man files [OK]

Hint: Use whereis to find all related command files [OK]

Common Mistakes:

• Using which to find all files
• Using locate without filtering results
• Running find without knowing its slowness