Profound Linux For Developers

By Onder Teker

This book contains topics about Linux for developers as well as advanced users or administrators. The shells & commands together with expansion & substitutionare explained in detail. Process communication with pipes & redirection are explained. Scripting is covered for both developers and system experts at both fundamental and advanced level. Topics such as files, array, strings, declarations are added. Initialization scripts & crontab are explained. MySQL/MariaDB, PostgreSQL, MongoDB databases; Apache, NGINX, Tomcat web servers; C/C++, Java, JavaScript, Python development kits are included.

Author

Önder Teker, the author of the book, develops projects since the end of the 1990s, gives courses and lectures since the beginning of the 2000s, and produces printed and electronic books and visual courses since the beginning of the 2010s.

• Language: English
• Publisher: Godoro
• Release date: Nov 26, 2023
• ISBN: 9786259947815

Book preview

Profound

Linux

For

Developers

Önder Teker

Godoro Publishing

GODORO PUBLISHING

Publisher Certificate No: 40946

The Name Of The Book:

Profound Linux For Developers

Copyright © 2023 Godoro Publishing

The Author Of The Book:

Önder Teker

First Edition, December 2023, Istanbul

ISBN:

978-625-99478-1-5

Cover Design & Makeup:

Önder Teker

Printing & Binding:

Godoro

Special Printing Solutions

Atikali Mah. Fatih Cad. No: 81 D: 2

Fatih / İstanbul

Telefon : [phone]

http://www.godoro.com

GODORO PUBLISHING

Atikali Mah. Fatih Cad. No: 81 D: 2

Fatih / Istanbul

Phone : [phone]

http://www.godoro.com

Shell & Commands

In this section, basics about the operating system commands and the shell which interprets commands are explained.

Command

General information about commands are provided here.

Command & Interpreter

In this section, what a command and interpreter means is explained.

Command

An instruction given as a few words is called a command. It is the thing a user requires the computer to do. In general, it is a word. For example, the expression below can be a command

perform

In many cases, it is shortened. For example, perform the important operation may be shortened as below:

pio

Argument

The data given to a command is called an argument. For example, the expression below

perform ABC

means the perform command will be executed with the ABC argument.

A command can take multiple arguments. Example

perform ABC 123 xyz

Or, no argument is needed. Example

perform

Option

A command may run in more than one way. The extra requirement to a command is called an option. There may be multiple options. For example, the perform command can be run in a slow mode or a fast mode. Or a direct mode or an indirect mode. In that case, the call will be as below:

perform -slow -indirect

In some cases, an option is mandatory and in some others, it is optional. If it is mandatory and not given, an error message is printed.

Parameter

In some cases, an option needs a value. It is called a parameter. For instance, let us assume that the option speed. It needs the speed value. An example can be written as below:

$ perform -speed 100

This means the value given to the speed option is 100.

A parameter can look like an argument. But a command will understand it as a parameter from its locations. For example, in the call below:

$ perform -speed 100 200

the first number is a parameter if the option takes one parameter. The second number is an argument for the command.

In some cases, the parameter value is given after the option name. If it is a letter, the value is given just after it. Example:

$ perform -s100 200

If it is a word, an equals (=) sign can be used. Example:

$ perform --speed=100 200

Exit Code

Each command or program returns an exit code as a result. If it is zero (0) it means the execution is a success. If any number other than zero is returned, it means the call is a failure.

Interpreter

The program which executes commands is called interpreter. Reading a command and trying to understand what it is and how to run it is called to interpret. The action is named interpretation. Each command has one file where instructions are kept. The interpreter finds that file, gives the arguments.

Command Line

A command is entered in a line and after pressing Enter key they are executed. The line in which commands are entered is called the command line. A command can be written in more than one line or more than one command can be executed in a single line. Sometimes all the calls of a command, the name, arguments and parameters are called a line since a command takes a line in general. The call of a command may be thought as a sentence which can take a line or more.

Script

Instead of running command one by one in a command line, they can be put into a file and executed from there. The extension of this file is something line sh (shell). This file is called a script. In a script file, some features of programming languages such as conditions or loops can be used. The task containing many commands and needs some logic are written to shell scripts and executed from there.

Comment

A script file or a file used for definitions may have some explanations. It is called a comment. It is given after hash (#) symbol. Example :

# This is done becuase it is needed

Sometimes, a command or a piece of executable statement can be turned into a comment. For example, the lines below:

# echo Godoro

# department = Publishing

may look like a command but it does not work. Because, it is left as a comment. In order to activate it, the hash (#) symbol must be removed as below:

echo Godoro

department = Publishing

Command Line

The place where commands  for a shell are entered is called the command line. Here are some details about it.

Command Prompt

The expression after which commands are entered is called command prompt.  In general some words or expressions together with a symbol such as a dollar ($)  or hash (#) are used to show the command line. After that, a cursor may be blinking to show where the keys pressed in a keyboard will be displayed. For example, the command prompt looks like below:

$ _

Here the underscore represents the blinking cursor. Itshows the characters entered using the keyboard. It will move right each time a key is pressed. For example, if per is written, the command prompt will be as below:

$ per_

Multiple Commands

In one line, multiple commands can be entered by the semicolon (;) symbol.  For example, the example below:

$ mycommand ; yourcommand

will execute the first command and then the second.

There will be no relation between the two. It is the same as calling the method in two separate lines as below:

$ mycommand

$ yourcommand

Clear

The output printed on the terminal can be cleaned by the clear command. Its usage is as below:

$ clear

After this call, only the command line will stay and the other text will be cleared.

Reset

The reset command put the terminal to its initial state. It clears the output but also removes all the settings done by the user. Its usage is as below:

$ reset

This command can be used when the terminal is in a mess. Sometimes, a user may cause the terminal to behave as if it is broken. In those cases, calling the reset command will fix the problem.

Command Prompt

In this section, components of the command prompt and ways to customize them are explained.

Admin

If the user is an admin, a hash (#) symbol  can be used in some environments.

# _

Machine Name

In some cases, the name of the machine or computer or host can be written before the $ symbol. Example:

myachine $ _

Username

In some cases, a user name is added and the two pieces of information are written in square brackets ([]). Example:

[ myuser@mymachine ] $ _

Home

If a user works in their home directory, the tilde (~) symbol is added as below:

[ myuser@mymachine ~] $ _

Working Directory

The curent directory or working directory can be displayed in the command prompt. For example, the prompt may be as below:

mymachine:/usr/bin$

This shows that current directory is as below:

/usr/bin

Prompt String

The command prompt can be changed by the PS1 (prompt string 1) variable. For example, the call below:

PS1=Godoro>

will change the prompt to this:

Godoro> _

There are some escape characters to customize the prompt. For example u means username, h means hostname, w means working directory. The call below:

PS1="\u@\h - \w Godoro > "

will make the prompt as below:

myuser@myhost - ~/mydirectory Godoro > _

Prompt Command

There is another way to customize the command prompt. The PROMPT_COMMAND variable can be declared the command to produce the prompt is declared.  For example, the call below:

PROMPT_COMMAND=date +'%y-%m-%d %H:%M >'

will change the prompt to this:

23-09-18 17:52 >

Command Syntax

The thing the user asked from the operating system is called command.

Execute

A command is executed by writing its name and pressing the Enter key. For example, if the name of the command is mycommand, it can be executed by writing its name as below:

$ mycommand

and pressing the Enter key.

In most cases, programs or utilities which is called from a command line is also can be thougt as commands. For example, a program named myutility.exe can be called as below:

myutility.exe

In most case, the extension can be omitted as below:

myutility

Argument

A command may take some extra information named arguments to perform a task. This is given after the command separated by a space ( ) symbol. For example, if 123 is to be given to the mycommand command, the call will be as below:

mycommand 123

More than one argument can be supplied. For example, the call below:

mycommand 111 222 333

takes 3 arguments.

Argument, Option, Parameter

If an argument is a value to the command, its called a parameter. If the argument is used to change the behavior of a command, it is called an option. The general syntax is as below:

command -opt1 -opt2 -opt3 param1 param2

Since a parameter does not have a name, their position is important. The second one must not be used instead of the first. On the other hand, the order of the options are not so important.

In some cases, an option also can take some value by using equals (=) sign. Example:

command -opt1=ABC -opt2=123

Technically the name of a command or program is also called an argument at index 0.

Option - Word

A command may be called by some options. A command will be executed according to these options. If it is a word, an option is given after two dash (--). For example, an option named fast may be given as below:

$ mycommand --fast

Option - Letter

In most cases, an option can be given by a single letter. Only one dash (-) is used. For example, instead of fast the f letter can be used as below:

$ mycommand -f

The case is important. The call below may refer to a different option from the one above:

$ mycommand -F

The letter may not be the inital of the word related to the option. Especially, if there are two options with the same initial, a different letter can be used. For instance, furious  may be represented by upper case F. The call below:

$ mycommand -fast -furious

can be written as  below:

$ mycommand -f -F

Multiple Options

More than one option may be supplied to a command. For example, the call below:

$ mycommand --fast --deep --careful

have three options.

The short forms can be used as below:

$ mycommand -f -d -c

The letters can be given after a single dash (-) sign as below:

$ mycommand -fdc

Advanced Syntax

In this section some advanced features are explained.

Range

In some cases, a command can be called by an argument with multiple values. For this, the curly brackets ({}) can be used. The values can be given one by one with