1. pwd: Print Working Directory

---

The pwd utility outputs the absolute path of the current working directory. It is primarily used to verify your location within the filesystem hierarchy before executing path-dependent operations.

Syntax

pwd [options]

Usage Example

$ cd /var/log/nginx
$ pwd
/var/log/nginx

2. cd: Change Directory

---

The cd command modifies the shell's current working directory. It supports both absolute and relative path resolution.

Syntax

cd [target_path]

Common Path Shortcuts

Shortcut	Behavior
~	Navigates to the current user's home directory
-	Returns to the previous working directory
.	References the current directory
..	References the parent directory
/	References the filesystem root

Usage Examples

# Navigate using an absolute path
$ cd /etc/sysconfig
$ pwd
/etc/sysconfig

# Jump to home directory
$ cd ~
$ pwd
/home/operator

# Return to the previous location
$ cd -
/etc/sysconfig

# Traverse upward using relative paths
$ cd ../../usr/local
$ pwd
/usr/local

3. ls: List Directory Contents

---

The ls command displays files and directories within a specified path. It provides metadata such as permissions, ownership, size, and modification timestamps when combined with formatting flags.

Syntax

ls [options] [target_path]

Frequently Used Options

Flag	Description
-l	Long format: displays permissions, owner, group, size, and timestamp
-a	Includes hidden files (those starting with a dot)
-i	Displays the inode number for each entry
-d	Lists directory entries themselves, not their contents
-t	Sorts output by modification time (newest first)
-r	Reverses the sorting order
-R	Recursively lists subdirectories

Usage Examples

# Verify file existence and view attributes
$ ls -l /etc/hostname
-rw-r--r-- 1 root root 14 Oct 12 09:30 /etc/hostname

# List multiple targets simultaneously
$ ls -l /etc/hosts /var/data/config.json
-rw-r--r-- 1 root root 221 Oct 12 09:30 /etc/hosts
-rw-r--r-- 1 app  app  1045 Nov 05 14:22 /var/data/config.json

# Display hidden files in the home directory
$ ls -a ~/
.  ..  .bash_history  .bashrc  .config  documents  .ssh

# Show inode numbers for current directory entries
$ ls -i
524891 config.yaml  524892 deploy.sh  524893 .env

4. mkdir: Create Directories

---

The mkdir utility generates new directories. It can create single folders, multiple sibling folders, or nested hierarchies in a single invocation.

Syntax

mkdir [options] directory_name [directory_name...]

Key Options

Flag	Description
-p	Creates parent directories as needed (no error if existing)
-m	Sets explicit permissions during creation
-v	Prints a message for each created directory

Usage Examples

# Create multiple sibling directories
$ mkdir src build dist
$ ls -d src build dist
build  dist  src

# Generate a nested directory structure
$ mkdir -p archive/2023/november/reports
$ tree archive
archive
└── 2023
    └── november
        └── reports

3 directories, 0 files

5. cp: Copy Files and Directories

---

The cp command duplicates files or directory trees to a specified destination. When copying directories, recursive mode must be enabled.

Syntax

cp [options] source destination

Key Options

Flag	Description
-r / -R	Recursively copies directories and their contents
-p	Preserves mode, ownership, and timestamps
-a	Archive mode: equivalent to -dR --preserve=all
-i	Prompts before overwriting existing files
-f	Forces overwrite without prompting
-b	Creates a backup of each existing destination file
-t	Treats the first argument as the destination directory

Usage Examples

# Copy and rename in one step
$ cp app.conf /backup/app.conf.bak

# Copy multiple files into a target directory
$ cp data.csv metrics.csv /backup/

# Recursively duplicate a directory tree while preserving attributes
$ cp -a module_core/ /backup/modules/
$ ls -l /backup/
total 12
-rw-r--r-- 1 user user   0 Oct 20 14:10 app.conf.bak
-rw-r--r-- 1 user user   0 Oct 20 14:11 data.csv
-rw-r--r-- 1 user user   0 Oct 20 14:11 metrics.csv
drwxr-xr-x 2 user user  40 Oct 20 14:12 modules

6. rm: Remove Files and Directories

---

The rm utility deletes filesystem objects. It operates permanently by default, bypassing any trash or recycle bin mechanisms.

Syntax

rm [options] target [target...]

Key Options

Flag	Description
-r / -R	Recursively removes directories and contents
-f	Ignores nonexistent files and never prompts
-i	Prompts before every removal
-d	Removes empty directories

Usage Examples

# Delete a single file
$ rm draft_notes.txt

# Force-remove a directory and all nested contents
$ rm -rf old_cache/

# Interactive deletion for safety
$ rm -i temp_session.log
rm: remove regular empty file 'temp_session.log'? y

7. mv: Move or Rename Files and Directories

---

The mv command relocates filesystem objects or changes their names. Unlike copying, moving updates directory entries without duplicating data blocks on the same filesystem.

Syntax

mv [options] source destination

Key Options

Flag	Description
-f	Overwrites destination without prompting
-i	Prompts before overwriting
-n	Prevents overwriting existing files
-b	Creates a backup before overwriting

Usage Examples

# Relocate a script to a binary directory
$ mv setup.sh /usr/local/bin/

# Rename a file in place
$ mv readme.md README.md

# Move multiple logs into an archive folder
$ mv access.log error.log /var/log/archive/

# Relocate an entire directory
$ mv legacy_app/ /opt/deprecated/

8. tree: Display Directory Structure

---

The tree command renders a visual, indented representation of directory hierarchies. It is highly useful for auditing project layouts or verifying nested structures.

Syntax

tree [options] [target_directory]

Key Options

Flag	Description
-L <depth>	Limits display to a specified number of levels
-d	Lists directories only
-a	Includes hidden files
-f	Prints the full path prefix for each entry

Usage Examples

# Visualize a project layout
$ tree project_root/
project_root/
├── config
│   └── settings.json
├── src
│   ├── main.py
│   └── utils.py
└── tests
    └── test_main.py

3 directories, 4 files

# Limit output to two levels deep
$ tree -L 2 /var/www/
/var/www/
├── html
│   ├── index.html
│   └── assets
└── logs
    ├── access.log
    └── error.log

3 directories, 3 files

9. du: Estimate File Space Usage

---

The du utility calculates disk consumption for files and directories. Its essential for identifying storage bottlenecks and monitoring partition utilization.

Syntax

du [options] [target_path]

Key Options

Flag	Description
-s	Displays only a total for each argument
-h	Prints sizes in human-readable format (K, M, G)
-a	Includes individual file sizes in the output
-c	Produces a grand total

Usage Examples

# Summarize directory size in readable format
$ du -sh /var/www/html
142M    /var/www/html

# Identify largest subdirectories within a path
$ du -h --max-depth=1 /var/log | sort -rh | head -n 5
85M     /var/log
42M     /var/log/journal
28M     /var/log/apache2
10M     /var/log/syslog
5.2M    /var/log/kern.log