Bash Shell Scripting

Bash Shell Read

Bash Shell provides read command that enables a developer to read input from the user. You can also use read command to read from the file as well.

Syntax of Bash Shell Read Command

read [options] variable

Here, the entered data is stored in a variable.

Command line options of Bash Shell Read Command

Options	Description
-p "Message"	It is used to display message and shows prompt just after that message. You can see its usage here- How to read input from user in Bash Shell?
-s	This option prevents the entered character from being displayed on the screen. Used for inputting password from the user. Example of this option can be seen here- How to prompt for password in Bash Shell?
-t NumberOfSeconds	Here, we mention the number of seconds for the read command to wait for input. Example read -t 5 firstnumber
-n NumberOfCharacters	It limits the user from entering specified length characters. Example read -n 2 choice

How to limit user from entering characters of specified length in Bash Shell?

Use -n option and specify the number of characters that you want to read from the user. Below example will show its usage-

#Bash Shell script to check the usage of -n option
read -n 1 -p "Do you want to continue(Y/N): " choice
case $choice in
Y | y) 
      echo
      echo "Go on";;
N | n)
      echo
      echo "Goodbye"
      exit;;
esac

Output of the above program

Do you want to continue(Y/N): Y
Go on

Explanation of the above code-

read -n 1 -p "Do you want to continue(Y/N): " choice

We want user to enter Y or N and does not want user to enter complete Yes or No. To achieve this, we have specified 1 to -n option.

How to set the timer for inputting characters in Bash Shell?

You might face a situation in which your script is waiting for the user to enter data. And you want your script to go one then in that case, use -t option to mention the number of seconds for the read command to wait for input.

#Bash Shell script to check the usage of -t option
read -t 5 -p "Enter your name: " name
if [ $name ];
then
  echo "Hello $name, How are you?"
else
  echo "You are too slow!"
fi