Getting Started With The Command Line

What is Command Line?

A user interface where one can enter text prompts to execute commands or automate tasks.

The terms: Command Line, Bash, Shell, Terminal, Command Prompt, are used interchangeably but they all generally mean the same thing. Below are some quick descriptions for each term.

• Command Line Interface (CLI) is a user interface where users type in commands and view outputs printed on the screen.

• Bash is a shell and command language in Linux.

• Shell is a software that interprets and executes the various commands that we type in the CLI.

• Terminal, is a CLI application in Mac OS.

• Command Prompt, is a CLI application in Windows OS.

Benefits of using the Command Line

While many users are accustomed to using a graphical user interface (GUI), the command line offers the following benefits:

• Direct interaction with the computer, with no overhead processing from the GUI, allowing faster and more efficient execution of tasks.
• Automation of commands and tasks by running scripts.
• Makes you feel like a hacker (sort of)

What can we use it for?

In my day-to-day, I use the command line to:

• Inspect details of my localhost/servers/applications/processes
• Navigate and manipulate files and folders (Filesystem Management)
• Access servers over networks
• Run applications
• Debug logs
• Write and run scripts to automate tasks/applications
• Version Control (Git)

Note: The above list is not exhaustive, use cases will differ between individuals

Cheatsheet

The below cheatsheet is a compilation of commands that I either frequently used or found useful along the way when I approach the command line.

General Usage
Command	Usage
date	Print current date and time
exit	Close current session
history	Check the history of used commands
hostname	Print name of host system
sudo	Run command as an root/administrator
sudo shutdown -h now	Shutdown computer
sudo shutdown -r now	Restart computer
sudo su -	Log in as an root/adminstrator
whoami	Prints current user

Filesystem management
Command	Usage
cat filename	Read and print content from file (Fast for reading small contents) Use “less filename” for viewing large contents page by page For Windows, use “filename”
cd	Change directory to home
cd -	Change to previous directory
cd ..	Change to parent directory
cd dirname	Change directory to specific directory
cd ~	Change to home directory
clear	Clear the screen/Remove previously typed commands For Windows, use “cls”
cp -r dirname1 dirname2	Copy contents recursively from directory 1 to directory 2 For Windows, use “robocopy dirname1 dirname2”
cp filename dirname	Copy file to a directory For Windows, use “copy filename dirname”
ditto -V dirname1 dirname2	Copy all contents of one folder to another folder
echo “Hello World”	Display message “Hello World”
echo “Hello World” > filename	Create a file with “Hello World” or appends “Hello World” to file
find dirtosearch -name filename	Find location of a program
grep regex dirname	Search for text patterns in directory
grep regex filename	Search for text patterns in filename
head -100f filename	Show the first 100 lines of file in real-time
head -n 5 filename	Show first 5 lines of file
ls	List directory contents. For Windows, use “dir”
ls -a	List contents including hidden files (Files that begin with a dot)
ls -l	List contents with more info including permissions (long listing)
ls -r	List contents reverse order
mkdir dirname	Make directory
mv dirname1 dirname2	Move directory from directory 1 to directory 2 For Windows, use “move” instead of “mv”
mv filename dirname	Move file to directory
mv filename1 filename2	Rename file or folder from file 1 to file 2 For Windows, use “ren filename1 filename2”
mv filename1 filename2 -v	Rename Verbose - print source/destination directory
open dirname	Open a file/folder. For Windows, use “start filename“ For Linux, use “xdg-open filename”
ps -ef » filename	Append the piped output of ps -ef to file ”>” : Overwrite existing file or creates a file if the file is not present in directory ”»”: Append existing file or creates a file if the file is not present in directory.
pwd	List path to the working directory For Windows, use “cd”
rm -i filename	Remove directory
rm -r dirname	Remove directory with contents recursively
rm -rf dirname	Remove directory with contents recursively and ignore non-existent files and arguments, no confirmation prompt
rm ./*	Remove everything in the current folder
rm filename	Remove file For Windows, use “del filename”
rmdir dirname	Remove empty directory
tail -10 input_file | grep “Hello World” » output_file	Pipe last 10 lines of input_file and grep texts matching “Hello World” to output_file.
tail -100f filename	Show the last 100 lines of file in real-time. Useful for inspecting running logs
tail -n 5 filename	Show last 5 lines of file
tar -czvf dirname.tar.gz dirname	Create tarball
tar -tzvf dirname	See what is in the tarball
tar xzvf dirname.tar.gz	Extract tarball
tar flags	c : Creates Archive x : Extract the archive f : creates archive with given filename t : displays or lists files in archived file u : archives and adds to an existing archive file v : Displays Verbose Information A : Concatenates the archive files z : Zip - tellstar command that creates tar file using gzip j : filter archive tar file using tbzip W : Verify a archive file r : update or add file or directory in already existed .tar file
touch filename	Create a file
vi filename	Create/Edit a file in VIM

Server and Network Management
Command	Usage
curl -o path to file	Download file
nc -v serverName	Initiate a telnet connection to server
netstat	Show network status and protocol statistics
ping/curl serverName	Ping or curl a server
scp dest1 dest2	Remote copy filepath from dest 1 to dest 2 where dest1 and dest2 can be written as user@remote_server:filepath
ssh serverName	Initiate SSH connection to server

Disk Management
Command	Usage
df -h	Check free disk space
du	List subdirectory memory usage
du -s	Check storage for specific file

Process Management
Command	Usage
kill PID	Kill processes using PID
ps -ax	Show all running processes
ps -ax | grep <name/pid/regex>	Search process using name/PID/regex
top	Display live process statistics
top -o rsize	Display processes with the highest memory usage
nohup file > logFile &	Run process in the background (&) and pipes the standard output to log file
nohup file > logFile 2>&1 &	Run process in the background (&) and pipes both standard output and error (2>&1) to log file

Conclusion

The command line is the bread and butter application for all computer systems. Not only will it automate and speed up your day-to-day development work, it serves as a starting point for you to run, inspect and monitor the applications and filesystems of servers directly. For many who are initially starting out, this application looks and feels like a “black box”. But rest assured, with sufficient exposure and practise, you will eventually master it and enjoy the many benefits this application brings to your everyday workflow.

Sources

1. 11 Terminal Commands You Should Know
2. bradtraversy/terminal-commands
3. Most useful Terminal commands for macOS (2023 Updated)
4. Windows vs. Mac: 70+ Common and Helpful Keyboard Shortcuts
5. The Difference Between “>” and “»” in Linux
6. An A-Z Index of the Linux command line: bash + utilities.
7. Stackoverflow - What does “2>&1” mean?