mkdir (create directories) in Linux CLI - Time & Space Complexity

Time Complexity: mkdir (create directories)

O(n)

Understanding Time Complexity

When creating directories using the mkdir command, it's helpful to understand how the time it takes grows as you create more directories.

We want to know how the work done by mkdir changes when the number of directories increases.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

for dir in dir1 dir2 dir3 dir4 dir5; do
  mkdir "$dir"
done

This script creates five directories one by one using a loop.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The mkdir command inside the loop creates one directory per iteration.
• How many times: The loop runs once for each directory name, so it runs n times if there are n directories.

How Execution Grows With Input

Each directory creation takes roughly the same amount of time, so total time grows as you add more directories.

Input Size (n)	Approx. Operations
10	10 mkdir commands run
100	100 mkdir commands run
1000	1000 mkdir commands run

Pattern observation: The total work grows directly with the number of directories you create.

Final Time Complexity

Time Complexity: O(n)

This means the time to create directories grows linearly with how many directories you want to make.

Common Mistake

[X] Wrong: "Creating multiple directories with mkdir is always instant no matter how many directories."

[OK] Correct: Each directory creation takes some time, so more directories mean more total time, even if each one is quick.

Interview Connect

Understanding how simple commands like mkdir scale helps you think clearly about scripts and automation tasks in real work.

Self-Check

"What if we used mkdir -p to create nested directories in one command? How would the time complexity change?"

Practice

1. What does the mkdir command do in Linux?

easy

A. Deletes files from the system

B. Creates new directories (folders) to organize files

C. Lists files in a directory

D. Changes the current directory

Solution

1. Step 1: Understand the purpose of mkdir

   The mkdir command is used to create new directories (folders) in Linux.

2. Step 2: Compare with other commands

   Deleting files is done by rm, listing files by ls, and changing directories by cd.

3. Final Answer:

   Creates new directories (folders) to organize files -> Option B

4. Quick Check:

   mkdir = create folders [OK]

Hint: mkdir always makes folders, not files or lists [OK]

Common Mistakes:

• Confusing mkdir with rm or ls commands
• Thinking mkdir deletes files
• Assuming mkdir changes directories

2. Which of the following is the correct syntax to create a directory named projects?

easy

A. mkdir: projects

B. mkdir -d projects

C. mkdir projects

D. mkdir > projects

Solution

1. Step 1: Recall mkdir syntax

   The basic syntax to create a directory is mkdir directory_name. No extra symbols or options are needed for a simple directory.

2. Step 2: Evaluate options

   mkdir -d projects uses a non-existent -d flag, mkdir: projects uses invalid colon syntax, and mkdir > projects uses redirection which is incorrect here.

3. Final Answer:

   mkdir projects -> Option C

4. Quick Check:

   Simple mkdir = mkdir directory_name [OK]

Hint: Use just mkdir plus folder name to create one folder [OK]

Common Mistakes:

• Adding unnecessary flags like -d
• Using colons or symbols incorrectly
• Trying to redirect output with >

3. What will be the result of running this command?

mkdir -p home/user/docs

medium

A. Creates home, user, and docs directories if they don't exist

B. Creates only the docs directory if home/user exists

C. Shows an error because -p is invalid

D. Deletes existing home/user/docs directory

Solution

1. Step 1: Understand the -p option

   The -p option tells mkdir to create parent directories as needed without error if they already exist.

2. Step 2: Analyze the command effect

   This command creates the full path home/user/docs including any missing directories in the path.

3. Final Answer:

   Creates home, user, and docs directories if they don't exist -> Option A

4. Quick Check:

   mkdir -p = create nested folders [OK]

Hint: Use -p to make all needed folders in one go [OK]

Common Mistakes:

• Thinking -p only creates the last folder
• Assuming -p is invalid or causes errors
• Confusing mkdir with delete commands

4. You run mkdir folder1 folder2 folder3 but get an error. What is the most likely cause?

medium

A. You need to use -p to create multiple folders

B. mkdir cannot create more than one folder at a time

C. You must create folders one by one with separate commands

D. One or more folder names contain spaces without quotes

Solution

1. Step 1: Check mkdir multiple folder support

   mkdir supports creating multiple folders by listing names separated by spaces.

2. Step 2: Identify common error with spaces

   If folder names contain spaces, they must be quoted or escaped. Otherwise, mkdir treats parts as separate names causing errors.

3. Final Answer:

   One or more folder names contain spaces without quotes -> Option D

4. Quick Check:

   Spaces in names need quotes for mkdir [OK]

Hint: Quote folder names with spaces to avoid errors [OK]

Common Mistakes:

• Thinking -p is needed for multiple folders
• Believing mkdir only creates one folder at a time
• Not quoting folder names with spaces

5. You want to create a project folder structure with src, bin, and docs inside myproject in one command. Which command achieves this?

hard

A. mkdir -p myproject/src myproject/bin myproject/docs

B. mkdir myproject && mkdir src bin docs

C. mkdir -p myproject/src/bin/docs

D. mkdir myproject/src myproject/bin myproject/docs

Solution

1. Step 1: Understand nested folder creation

   Using -p allows creating parent directories and nested folders in one command without errors.

2. Step 2: Analyze each option

   mkdir myproject/src myproject/bin myproject/docs lacks -p so may fail if myproject doesn't exist. mkdir -p myproject/src myproject/bin myproject/docs correctly uses -p to create all paths. mkdir -p myproject/src/bin/docs creates nested folders incorrectly. mkdir myproject && mkdir src bin docs creates folders separately, not in one command.

3. Final Answer:

   mkdir -p myproject/src myproject/bin myproject/docs -> Option A

4. Quick Check:

   Use mkdir -p with full paths for multiple nested folders [OK]

Hint: Use mkdir -p with all paths to create nested folders at once [OK]

Common Mistakes:

• Omitting -p when parent folder doesn't exist
• Creating nested folders incorrectly as one path
• Running multiple mkdir commands instead of one