Linux Command Line Tools - Paiet/Tech-Journal-for-Everything GitHub Wiki

Command-Line Basics
- Exploring Your Linux Shell
  - Bourne Again Shell (bash)
    - Based on the Unix Bourne shell (sh)
    - bash is the default shell in most Linux systems
  - csh or the C Shell utilizes a syntax that is liken to the C programming language
  - tcsh based off of csh
    - More bash-like but still different
    - The T stands for TENEX. An OS that inspired the author of tcsh
  - There are 2 types of default shells
    - Default Interactive Shell
      - The shell that the user works with to enter commands
    - Default System Shell
      - The shell that they system uses to run startup scripts
      - Typically the file /bin/sh points to the default system shell
        
        Usually /bin/bash in Linux
        
        Points to /bin/dash in Ubuntu
- Using a Shell
  - Starting a shell
    - Linux can drop you straight to a shell after startup
    - In a GUI environment you can start a terminal emulator
      - XTERM, Konsole, Terminal, gnome-terminal
      - uname -a returns all the system information
  - Internal vs. External Commands
    - Internal commands are built-in to the shell
    - External commands are programs that run in the shell but aren't native to the shell
    - Internal command examples
      - cd Change Directory
        
        cd ~/sally is the same as cd /home/sally
      - pwd Print Working Directory
      - echo prints a string of text
        
        echo Hello
        
        Useful when writing scripts and checking the content of environmental variables
      - exit terminates any shell
      - logout terminates only login shells
    - You can find out whether a command is internal or external by using the type command
      - type pwd
      - type cd
      - type bash
    - type -a will display different programs that use the same name
      - type -a cd
      - type -a pwd
    - Shell tricks and tips
      - Auto-complete commands with Tab
      - history shows list of previously used commands, usually the last 500
        
        !! lists and executes the last command
        
        !210 lists and executes command #210 in the list
        
        history -c clears the history
        
        The history is stored in ~/.bash_history
      - Ctrl+P/Up arrow Ctrl+N/Down arrow scrolls through recently used commands
      - Ctrl+R performs a reverse search of commands
      - Ctrl+S performs a forward search of commands
        
        Ctrl+G quits the search
      - Ctrl+A moves the cursor to the start of the line
      - Ctrl+E moves the cursor to the end of the line
      - Ctrl+Left or Right arrow keys move the cursor backward or forward a word at a time
        
        Esc+B/F performs the same action
      - Ctrl+K deletes from the cursor to the end of the line
      - Ctrl+X+Backspace deletes text from cursor to the beginning of the line
      - Ctrl+T transpose the character before the cursor with the character under the cursor
        
        Esc+T transposes the word
      - Ctrl+X+Ctrl+E quick launches the default text editor
- Exploring Shell Configuration
  - Shell configuration files are just plain text shell scripts
    - ~/.bashrc and /etc/profile
      - Make necessary changes to these files
      - $PATH add directories to search for executables
- Using Environment Variables
  - Variables are containers for data
  - System Variables and User-Created Variables
  - $TERM

Begin

$> PS1="My New Prompt$>"
My New Prompt$> export PS1
My New Prompt$> export PS1="Prompt$>"
Prompt$> echo $PS1

Using Environment Variables
- env lists all environmental variables
- unset removes the data from the variable
Getting Help
- man for the manual of a program
- man man to learn to use man
- man -k will perform a lookup
  - man -k "system information"
- man is divided into 9 sections
  - Some commands can reside in multiple sections
    - passwd resides in both sections 1 and 5
    - man defaults to the lowest numbered section
    - man 5 passwd will return the manual for section 5's entry for the passwd command
- info is like man but uses hypertext and has some internal options for navigating the manual
- help usually gives a succinct synopsis of use for built-in commands