Scripting essential

Bash built-in commands GNU manual:
https://www.gnu.org/software/bash/manual/html_node/Bash-Builtins.html

Built-in, Special built-in and POSIX Inherited command list:
https://www.computerhope.com/unix/bash/index.htm

Basic syntax and special characters

Character Description

#                 Used to add a comment, except when used as \#, or as #! when starting a script

\                 Used at the end of a line to indicate continuation on to the next line

;                 Used to interpret what follows as a new command to be executed next

$                 Indicates what follows is an environment variable

>                 Redirect output

>>                 Append output

<                 Redirect input

|                 Used to pipe the result into the next command

Parameters

Command substitution

Variables

To export the variable in order to be valid also for the child processes:

export VAR=value

or

VAR=value ; export VAR

where "VAR" is the variable we want to export.

When a child process modifies a variable, that remains within the child processes and it doesn't affect the variable of the parent process. In other words, exporting means copying and inheriting.

Functions

Entering a function in a script means:

1. Declaring a function
2. Calling a function

The function declaration requires a name which is used to invoke it. The proper syntax is:

function_name () {

   command...

}