Question: How to find list of all shell in the Linux, Unix or mac ?

Answer: $ cat  /etc/shells

this will list all shell  in the system.

Question: How to find current  active shell in the Linux, Unix or mac ?

Answer:  $SHELL variable contains the value of current shell.

echo $SHELL

Question:  What is shell  scripting?

Answer:  Shell script is series of command written in text file.

1. Shell script can take input from user , file and output from other program.

2.Shell  script helps to automate daily task.

Question:  How to write shell script ?

Answer:  Shell script writing contains following steps.

1. Create a file for shell script.

2.Change the permission of shell script file to execute.

$ chmod +x script-name

$chmod +755 script-name