Bash scripting is a way to automate tasks on Linux and macOS systems. It involves writing a series of commands in a plain text file, which is then executed by the Bash shell.

• pwd: Print Working Directory.

  ~$ pwd
  /home/ubuntu
  

• whoami: print the current username of loggedin user.

  ~$ whoami
  ubuntu
  

• man: display thecomplete manual of the asked command in pages .

  ~$ man [option] [command]
   ~$ man ls
  

• help: display the brief information of the command.

  ~$ ls --help
  

  
  
  

File Manipulation:

• cd: Change directory to certain location by providing path from the start of root directory ('/') or current directory ('.').

  ~$ cd path
  

  Change the path to home Directory.

  ~$ cd /home
  

  " . " represent current directory so pwd i.e. (print working directory or current working directory path) will not change

  ~$ cd .
  

  change to parent directory

  ~$ cd ..
  

  change to home directory

  ~$ cd ~
  

  change to two level up of current directory (if pwd is /home/ubuntu then after this command pwd become root ('/') directory.

  ~$ cd ../..
  

• ls: List the contents of a directory.
  

  ~$ ls
  

  List the hidden content in the Directory.

  ~$ ls -a
  

  List the given permission (using ls -l) and hidden content (ls -a) in the Directory.

  ~$ ls -la
  

  List the content of the Directory using the path.

  ~$ ls /path
  

  
  

• mkdir: Create a new directory. Using -p you can create subdirectories.

  ~$ mkdir folder_name1  -p folder_name1/folder_name2
  

• touch: Create an empty file.

  ~$ touch myfile.txt
  

  Create Multiple files using single command

  ~$ touch file{1..5}.txt
  file1.txt file2.txt file3.txt file4.txt file5.txt
  

• cp: Copy a file or directory. This command creates a copy of the source_file at the specified destination_path

  ~$ cp source_file destination_path
  

  Copy multiple files to a destination_path

  ~$ cp a.txt b.txt c.txt new/
  

• mv: Move or rename a file or directory. (e.g. mv file1.txt renamed_file.txt renames file1.txt)

  ~$ mv source_file destination_path
  

• rm: Remove a file or directory (use with caution!). (e.g. rm file1.txt removes file1.txt)

  `$ rm file.txt
  

  Remove the Non Empty Directory Recursively.

  `$ rm -r folder
  

  Remove the Non Empty Directory Recursively and forecfully.

  `$ rm -rf folder
  

• echo: Print text to the terminal. (e.g. echo Hello World! prints "Hello World!")

  ~$ echo "Hello World"
  Hello World
  ~$ echo target.com
  

  Store the content in a file

  ~$ echo "Hello World" > hello.txt
  ~ $ cat hello.txt
  Hello World
  

  Overwrite the content of a file

  ~$ echo "World" > hello.txt
  ~ $ cat hello.txt
  World
  

  Append the content of a file

  ~$ echo ", Good to see you" >> hello.txt
  ~ $ cat hello.txt
  Hello World, Good to see you
  

• cat: Display the contents of a file, also can overwrite and append the content in same way as the echo command.

  ~$ cat message.txt
  

• grep: Search for a pattern within a file. (e.g. grep error log.txt searches for "error" in log.txt)

  ~$ cat log.txt | grep "error"
  

• wc: word count from a file.

  ~$ wc -w hello.txt
  6 hello.txt
  
  ~$ wc -w > hello.txt
  6
  

  Count word from the input directly

  ~$ wc -w <<< "Hello World"
  2
  

Basic Scripting Elements:

• #: Used for comments (ignored by the shell).
• $: Used to access variables. (e.g. name="John" sets a variable named "name")

1. Scripting Bascis
   • Create a file with .sh extension

     ~$ touch basics.sh
     

   • open the file using nano or vim editor using command:

     ~$ nano basics.sh
     

     or

     ~$ vim basics.sh
     

     • Start writing in nano directly and to close ctrl+w + Enter and then ctrl+x to exit the editor.
     • For vim users: press i to write, then press esc to exit write mode, then press :wq where w is to save the file and q is to exit the editor.
       
   • start with this line #!/bin/bash which tells the type of Shell used by OS to interpret the script, where /bin/bash is the path of the bash shell.

     #!/bin/bash
     

   • Use of echo command to a read a text:

     ~$ echo Hello World
     

   • Execute the script:

     ~$ bash basics.sh
     Hello World
     

     or

     ~$ sh basics.sh
     

     or

     ~$ ./basics.sh
     

   • If there is some error occur such as permission denied then use this command and execute the script again:

     ~$ chmod u+x basics.sh
     

2. Variables