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Shell Commands for UNIX-Based Systems

This guide covers essential shell commands used in UNIX-based systems, including Linux and macOS. Some commands can also be used in Windows PowerShell to a certain extent.

Table Of Contents

  1. Terminology
  2. File System Navigation
  3. Flags
  4. Help and Manuals
  5. File Management
  6. File Input/Output
  7. Command-Line Utilities
  8. Redirection
  9. Pipelines
  10. Networking
  11. Other Useful Commands
  12. Third-Party Command-Line Tools
  13. Shell Scripting

Terminology

  • Shell: The interpreter that processes commands and returns the output.

    • UNIX examples: bash, zsh, fish
    • Windows examples: cmd, powershell

  • Terminal/Command-Line/Console: The program that allows you to interact with the shell.

    • Examples of terminal programs:
      • Default Terminal (macOS), Windows Terminal (Windows)
      • iTerm2 (macOS)
      • kitty
      • Hyper

File System Navigation

Commands to explore the file system:

  • ls: List files and directories in the current or specified directory.

  • pwd: Print working directory (shows the full path of your current directory).

  • cd: Change directory.

    File Paths:

    • Absolute Path: Full path from the root directory (e.g., /home/user/).
    • Relative Path: Path relative to the current directory (e.g., ./documents).
    • ./: Refers to the current directory.
    • ../: Refers to the parent directory.
    • /: Refers to the root directory.
    • ~: Refers to the user's home directory.
    • -: Refers to the previous directory.

Flags

Flags modify how commands behave:

  • Example: ls -lha
    • -l: Long format (more details like permissions and file size)
    • -h: Human-readable sizes (e.g., KB, MB)
    • -a: Show hidden files (files starting with .)

Help And Manuals

Find documentation directly from the command line:

  • --help: Displays usage information for a command.

    Example:

    grep --help

  • man <command>: Opens the manual page for the specified command.

    Example:

    man history

File Management

Basic commands to create, move, copy, and delete files or directories:

  • mkdir <directory>: Create a new directory.
  • touch <file>: Create an empty file or update the timestamp of an existing file.
  • open <directory>: Open directory in finder/folder.
  • cp <source> <destination>: Copy files or directories.
  • mv <source> <destination>: Move or rename files or directories.
  • rm <file>: Remove files or directories.
  • ln -s <target> <link_name>: Create a symbolic link.

File Input/Output

Commands to view or manipulate file content:

  • echo <text>: Output text to the console or write it to a file.

  • cat <file>: Display the contents of a file.

  • less <file>: View a file's content in a scrollable format.

    • In less: Press / to search, q to quit.

  • head <file> -n <number>: Display the first few lines of a file (default is 10).

  • tail <file> -n <number>: Display the last few lines of a file.

  • sed 's/<pattern>/<replacement>/<flag>' <file>: A stream editor used to perform basic text transformations on an input stream (files or piped input).

    Example:

    sed 's/REPLACE_EMAIL/randomperson@gmail.com/i' template.yaml

Command-Line Utilities

Useful utilities for working with text or files:

  • find <directory> -name <pattern>: Search for files and directories.

  • grep <pattern> <file>: Search for a specific pattern within a file.

  • sort <file>: Sort the lines in a file (defaults to alphabetical sorting).

  • wc <options> <file(s)>: Count lines, words, and characters in a file or input stream.

    • Options:
      • -l: lines
      • -w: words
      • -m: characters

    Example:

    wc sample.txt

wc -l sample.txt

# count files in current directory
ls | wc -l

Redirection

Redirect output or input between commands and files:

  • >: Redirect output to a file (overwrites).

    Example:

    echo "Hello universe!" > greetings.txt

  • >>: Append output to a file.

    Example:

    echo "This is Earth! Are there aliens out there?" >> greetings.txt

  • <: Use the content of a file as input to a command.

    Example:

    grep "Earth" < greetings.txt

Pipelines

Use the output of one command as the input for another:

  • |: Pipe the output from one command into another.

    Example:

    ls -l | grep "txt"

Networking

Basic networking commands you might encounter:

  • ping <hostname>: Check if a host is reachable.
  • curl <URL>: Fetch data from a URL.
  • ifconfig: Display network interfaces and IP addresses.

Other Useful Commands

A few more tools that might be helpful:

  • clear: Clear the terminal window.
  • history: Display a list of most recent commands.
    • !<number>: Execute the command on the input line number.
    • !!: Execute most recent command.
  • top: Display running processes.
  • htop: An improved version of top with a user-friendly interface.
  • df: Display disk space usage.
  • du: Show disk usage of files and directories.
  • ... more

Third-Party Command-Line Tools

In addition to built-in commands, there are several third-party tools that greatly extend the functionality of the command line.

These tools can be installed via the appropriate package manager for your system:

  • macOS: homebrew

  • Windows: chocolatey, scoop, or Windows Subsystem for Linux (WSL)

  • Linux: apt, yum, or pacman

    Neovim

    • Purpose: A modernized version of the classic vim text editor with better extensibility and performance.
    • Usage: Ideal for editing code or text directly in the terminal with powerful features like plugins and scripting support.
    • Command: nvim <file>
      • Example: nvim main.py

    fzf

    • Purpose: A general-purpose fuzzy finder for quickly searching files, directories, or command histories.
    • Usage: Fuzzy search for items in the terminal, works well when used in conjunction with other tools like git or ls.
    • Command: fzf
      • Example: find . -type f | fzf

    tmux

    • Purpose: A terminal multiplexer that allows you to open and manage multiple terminal sessions within a single window and allows session perssistence.
    • Usage: Run and manage multiple terminal sessions.
    • Command: tmux
      • Example: tmux new-session -s work

Shell-Scripting

You can use these commands directly in the terminal or include them in shell scripts for automation and repeatability. Here are some shell script examples:

To execute shell scripts use bash (need to have bash installed) before the filename like this:

bash greetings.sh

🚨 Do not execute unknown shell scripts on your system, unless you are absolutely sure what the script is doing!

This guide covers the basics, but the shell is vast—don't hesitate to explore new commands and tools!


Now go to the exercise.md file and practice some shell commands! Good luck!