Open Function Basics

• The open function documentation contains a lot of parameters
• The only positional parameter (file) specifies the path of the file to be read.

About Special Parameters

• Special parameters are set by the shell to store information about aspects of its current state
• Example 1: the number of arguments of the current script
• Example 2: the exit code of the last command.
• Their names are nonalphanumeric characters (for example, *, #, and _). Variables are identified …

About Parameters in bash

• A parameter is an entity that stores values.
• There are three types of parameters:
  • positional parameters
  • special parameters
  • variables
• We'll discuss here only positional parameters.
  (the other types will be discussed in other posts)

Positional Parameters

• These are arguments present you give …

Shell Script

• A shell script is a file containing one or more commands
• You could type those commands individually on the command line
• Here's the content of my first shell script:

1echo Hello World!

• We have already encountered the [echo] command in

  Command Types

• Now I have to give my file a name:
  • do not choose …

UNIX philosophy

Every operating system needs to interract with users.
The original UNIX philosophy said (among other things):
Write programs that do one thing and do it well. Write programs to work together.
This philosophy applis also to the interraction with the user, and the kernel.
In other words, the UNIX system …

About vi

• vi is a screen-oriented text editor originally created for the Unix operating system
• vi was a visual mode of the ex line editor, hence the name
• Being screen-oriented means that vi would work in a terminal you would use to connect textually to UNIX like systems (so telnet and ssh would be enough to use it) …

Let's create our own systemd service.

Our service program

• We'll use a simple bash script that endlessly outputs text into a log file:

1for (( ; ; ))
2do
3	echo "still running:" $(date)  >> /tmp/myprog.log
4	sleep 1
5done

• Save this in a file, make it executable by anyone (777) and copy to /usr/bin: …