BASH CLI Scripting - Paiet/Tech-Journal-for-Everything GitHub Wiki

What is BASH?
- Bourne Again SHell
- bashing together features of sh, csh, and ksh
- Created by Brian Fox in 1989 to replace the Bourne Shell
- Free BASH book: man bash or info bash
- Bash is a shell
  - What is a shell
    - A shell is a program that allow interaction with the OS
    - aka Command Line Interpreter
  - Interactive logon vs. interactive non-logon vs. non-interactive
    - Interactive logon: Start the computer, greeted with a non-graphical, text-based logon prompt. After logon, you are still in a text-based environment
    - Interactive non-logon: You start a shell by invoking it from the CLI, you start a shell by clicking an icon in the GUI, you don't provide logon credentials in either case
    - Non-Interactive: Runs without user interaction. I.E. startup scripts, init.d, rc.d, etc...
- Bash compared to other shells
  - sh
  - ksh
  - csh
  - tcsh
  - dash
  - zsh
  - rbash or restricted bash
    - rbash in Debian and bash -r in Redhat
    - man rbash in Debian and man bash then search for RESTRICTED in RH
    - invoke rbash and see what it's like to have it restrict you
  - cygwin (POSIX compliant Windows port)
- Bash is a scripting and programming language
  - Traditional programming languages are compiled and then run
  - Scripting is using a programming language that is interpreted as it is run with no need to compile it
  - Portability
    - Contains features than the traditional Bourne shell doesn't
      - BASH built-ins
      - Brace expansion
      - Extended test construction
- Also performs arithmetic
  - Has the ability to calculate numbers
    - This can be helpful at predicting numerical output in scripts
      - The file is 10kb today, it is growing by 2kb per day, how big will the file be in 10 days? If file reaches xKB in size then perform command y