/Ultimate-Guide-to-Shell-Scripting

This series of tutorials aimed at making the easiest guide to shell scripting in linux

Primary LanguageShell

Linux Scripting Tutorial

: Linux is a Unix-like, open source and community developed os for which is capable of handling activities from multiple users at the same time.

CONTENTS

  1. what-is-the-kernel

  2. Basic Linux Commands

  3. Command Line Essentials

  1. Shell Scripting

What is the Kernel

:The computer programs that allocate the system resources and coordinate all the details of the computer's internals is called the operating system or the Kernel.Users communicate with the OS through a program called the Shell

Basic Commands in the Linux Shell

  1. nano :nano is a text editor like vim or emacs. To use it just append the file name at the end to open a file. For Instance :nano textFile.txt

  2. pwd :Shows current Directory. Result :/home/kolynz

  3. ls :Lists all files in a directory. For Instance :ls /home/ #this will list the files in the home directory.and if its not accompannied with a path name it lists those in the current directory

  4. --help :This flag gives you a list of flags associated with a particular Command. For Instance :ls --help

  5. ls -l :List files in a long format. Results

-rwxrwxrwx 1 kolynzb kolynzb 282 Oct 21 21:15 desktop.ini
-rwxrwxrwx 1 kolynzb kolynzb 2224 Mar 1 10:14 Discord.lnk

permissions notsure user user-group not-sure date-created time-created file-name
r - read
w - write
x - executable

  1. cp :Copies files to a directory.For Instance cp test.txt /test will copy test.txt to /test directory.

  2. mv :Moves files. For Instance mv test.txt /test will move test.txt to /test directory.

  3. echo :Prints to the console. For Instance echo 'hello world'.

  4. cat :Concatenates contents of a test file to a terminal Syntax cat test.txt

  5. less :displays contents of a test file to a terminal in a new window Syntax less test.txt

  6. grep :Grabs data from file or command passed in. Syntaxmv --help | grep verbose #is the verbose command available for the move command and what it does

  7. touch :Creates a new file in current directory Syntax touch test.txt

  8. mkdir :Creates a new directory Syntax mkdir test

  9. cd :Moves into a new directory Syntax cd test/

  10. chmod :used to alter file permissions Syntax chmod +w text.sh #just adds a writing permission to the file or git add --chmod=+x . #makes all files added to staging area executable

: chmod 777 test.sh #makes this executable but these numbers are the user the group, others the file name in that order

number equavalent meaning description
0 0 nothing nobody get any information
1 1 execute execute
2 2 write write
3 2+1 w+x read and write
4 4 read read
5 4+1 r+x read and execute
6 6 r+x read and write
7 4+2+1 r+w+x All Permissions

so when one writes chmod 777 filename the first 7 allows the user to read, write and execute.The second applies to the user group and the last applies to everybosy else.

  1. man :displays a manual explaining a Command. Syntax man test

Command Line Essentials

CLI vs GUI

ClI(Command Line Interface) GUI(Graphical User Interface)
-console representational -Graphical represatation
-Difficult for beginners -Easy to use
-Faster OS -Os is slower
-Granular Control -Lesser Control
-Cooler 😎 😆

Remember Its a personal choice but for scripting its way better to use CLI :dissapointed_relieved:

what is CLI

:Is a text-based interface used to interact with a software and operating system by typing commands into the interface and receive a response in the same way.Easy to scale up and controll and less memory usage

Shell Scripting

:Shell is a command line intepreter.it translates commands entered by a user and converts them into a language understood by the Kernel

:Shell Script is a list of commands,which are listed in order of execution.a good shell script will have comments preceded with a hashtag sign,descibing the steps.

Shell Scripting Basics

There are two main broad types

BOURNE SHELL TYPES C SHELL TYPES
Bourne shell C shell
korn shell TENEX/TOPS C shell
Bourne-Again shell (BASH) Z shell
POSIX shell C shell

Lets begin

-create a file with .sh extension -add a Shebang at the top #! usr/bin/bash (bin/sh is the absolute path to the interpreter which is gotten by which bash)

  • 1. Variables

    • 1.Variables: Variable is a character string which we assign a value(Value assigned can be a number,text,filename,device,or other type of data). They are of 3 types 1.Local(that is preset in the current instance of a shell) 2.Environment/Global(Is avalable to any child process of the shell) 3.Shell(Set by the shell and is required by the shell in order to function correctly. Some of these are either global or local variables)

  • 1. Basic Operators

    • 1.Operators Arithmetic Operators

      Operator Purpose Example
      +(Addition) adds values on either side of the operator expr $a + $b will give 30
      -(Subtract) Subtract values on either side of the operator expr $a - $b will give -10
      *(Multiply) Multiply values on either side of the operator expr $a \* $b will give 200
      /(Division) Divides values on either side of the operator expr $a / $b will give 2
      %(Modulus) Divides values on either side of the operator returns reminder expr $a % $b will give 0
      =(Assignment) asigns left to right $a = $b assign a to b
      ==(Equality) Compares two characters and returns a boolean [$a == $b] return false
      !=(Not equal) Compares two characters and returns a boolean [$a != $b] return true

      Relational Operators

      Operator Purpose Example
      -eq checks equality of two operands [$a -eq $b] is not true
      -ne checks none equality of two operands [$a -ne $b] is true
      -gt checks if the 1st operand is greater of two operands [$a -gt $b] is not true
      -lt checks if the 1st operand is less of two operands [$a -lt $b] is true
      -ge checks if the 1st operand is greater or equal to the 2nd operand [$a -ge $b] is not true
      -le checks if the 1st operand is less or equal to the 2nd operand [$a -le $b] is true

      Boolean Operators

      Operator Purpose Example
      ! logical negation [!false]] is true
      -o logical OR [false -o true]] is true
      -a logical AND [false -a true ] is false

      String Operators

      Operator Purpose Example
      = checks equality of two operands [$a = $b] is not true
      != checks inequality of two operands [$a != $b] is true
      -z checks if given operand size is zero [-z $a] is not true
      -n checks if given operand size is non-zero [-n $a] is true
      str checks if str is not an empty string [-n $a ] is true

      File Operators(Bourne-shell-specific)

      Operator Purpose Example
      -b file checks if file is block special file [-b $file] is false
      -c file checks if file is character special file [-c $file] is false
      -d file checks if file is a directory [-d $file] is not true
      -f file checks if file is ordinary file as opposed to a special file or directory [-f $file] is true
      -g file checks if file has its group id set to (SGID) bit set [-g $file] is false
      -k file checks if file has sticky bit set [-k $file] is false
      -p file checks if file is a named pipe [-p $file] is false
      -t file checks if file descriptor is open and associated with the terminal [-t $file] is false
      -u file checks if file has its Set User ID bit(SUID) set [-u $file] is false
      -r file checks if file is readable [-r $file] is true
      -w file checks if file is writable [-w $file] is true
      -x file checks if file is executable [-x $file] is true
      -s file checks if file size is greater than zero [-s $file] is true
      -e file checks if file exists [-e $file] is true

  • 3. Loops

    • 3.Loops: These are loops -while -for -until -nested -break,continue

  • 4. Functions

    • 4.functions: Are Blocks of code that can be called multiple times -function with params -recurssive (calls itself)

  • 5. Use Cases - 4.functions: these are a few use cases t