Writing Learning Bash

docs/books/learning_bash/00-toc.md

@@ -0,0 +1,52 @@
+---
+title: Learning bash with Rocky
+---
+
+# Learning Bash with Rocky
+
+In this part, you will learn more about Bash scripting, an exercise that every administrator will have to perform one day or another.
+
+## Generalities
+
+The shell is the command interpreter of Linux.
+It is a binary that is not part of the kernel, but forms an additional layer, hence its name "shell".
+
+It parses the commands entered by the user and then makes them executed by the system.
+
+There are several shells, all of which share some common features.
+The user is free to use the one that suits him best among (among others):
+
+* the **Bourne-Again shell** (`bash`),
+* the **Korn shell** (`ksh`),
+* the **C shell** (`csh`),
+* etc.
+
+The `bash` is present by default on the main Linux distributions.
+It is characterized by its practical and user-friendly features.
+
+The shell is also a **basic programming language** which, thanks to some dedicated commands, allows :
+
+* the use of **variables**,
+* **conditional execution** of commands,
+* the **repetition** of commands.
+
+Shell scripts have the advantage that they can be created **quickly** and **reliably**, without **compiling** or installing additional commands. A shell script is just a text file without any embellishments (bold, italics, etc.).
+
+!!! NOTE
+
+    Although the shell is a "basic" programming language, it is still very powerful and sometimes faster than bad compiled code.
+
+To write a shell script, you just have to put all the necessary commands in a single text file.
+By making this file executable, the shell will read it sequentially and execute the commands in it one by one.
+It is also possible to execute it by passing the name of the script as an argument to the bash binary.
+
+When the shell encounters an error, it displays a message to identify the problem but continues to execute the script.
+But there are mechanisms to stop the execution of a script when an error occurs.
+Command-specific errors are also displayed on the screen or inside files.
+
+What is a good script? It is:
+
+* **reliable**: its operation is flawless even in case of misuse;
+* **commented**: its code is annotated to facilitate the rereading and the future evolutions;
+* **readable**: the code is indented appropriately, the commands are spaced out, ...
+* **portable**: the code runs on any Linux system, dependency management, rights management, etc.

docs/books/learning_bash/01-first-script.md

@@ -0,0 +1,109 @@
+---
+title: Bash - First script
+author: Antoine Le Morvan
+contributors: Steven Spencer
+update: 29-mar-2022
+---
+
+# Bash - First script
+
+In this chapter you will learn how to write your first script in bash.
+
+****
+
+**Objectives**: In this chapter you will learn how to:
+
+:heavy_check_mark: Write your first script in bash;
+:heavy_check_mark: Execute your first script;
+:heavy_check_mark: Specify which shell to use with the so-called shebang;
+
+:checkered_flag: **linux**, **script**, **bash**
+
+**Knowledge**: :star:     
+**Complexity**: :star:
+
+**Reading time**: 10 minutes
+
+****
+
+## My first script
+
+To start writing a shell script, it is convenient to use a text editor that supports syntax highlighting.
+
+`vim`, for example, is a good tool for this.
+
+The name of the script should respect some rules:
+
+* no names of existing commands;
+* only alphanumeric characters, i.e. no accented characters or spaces;
+* extension .sh to indicate that it is a shell script.
+
+```
+#!/usr/bin/env bash
+#
+# Author : Rocky Documentation Team
+# Date: March 2022
+# Version 1.0.0: Displays the text "Hello world!"
+#
+
+# Displays a text on the screen :
+echo "Hello world!"
+```
+
+To be able to run this script, as an argument to bash:
+
+```
+$ bash hello-world.sh
+Hello world !
+```
+
+Or, more simply, after having given it the right to execute:
+
+```
+$ chmod u+x ./hello-world.sh
+$ ./hello-world.sh
+Hello world !
+```
+
+!!! NOTE
+
+    Note that to execute the script, it has been called with `./` before its name.
+    The interpreter may refuse to execute a script present in the current directory without indicating a path (here with `./` before it).
+
+    The `chmod` command is to be passed only once on a newly created script.
+
+The first line to be written in any script is to indicate the name of the shell binary to be used to execute it.
+If you want to use the `ksh` shell or the interpreted language `python`, you would replace the line:
+
+```
+#!/usr/bin/env bash
+```
+
+with :
+
+```
+#!/usr/bin/env ksh
+```
+
+or with :
+
+```
+#!/usr/bin/env python
+```
+
+This first line is called the `shebang`.
+It is materialized by the characters `#!` followed by the path to the binary of the command interpreter to use.
+
+Throughout the writing process, you should think about proofreading the script, using comments in particular:
+
+* a general presentation, at the beginning, to indicate the purpose of the script, its author, its version, its use, etc.
+* during the text to help understand the actions.
+
+Comments can be placed on a separate line or at the end of a line containing a command.
+
+Example:
+
+```
+# This program displays the date
+date # This line is the line that displays the date!
+```