How to Wait for User Input in Bash [With 4 Practical Examples]

In Bash, the read command is commonly used for taking user input. Interestingly, it allows the scriptwriter to take pause and wait until the user enters some input or presses any key. Moreover, one can set a timeout using the -t option. We can even take different actions based on different inputs provided by the user. We are going to explore waiting for input Bash and how to effectively utilize this in Bash scripting.

4 Practical Examples of Waiting for User Input Using Bash Script

The read command is the default choice for taking user input in Bash scripting. In the subsequent examples, we are going to discuss how to use the read command to wait for user input and discuss their applications in detail.

1. Wait for Input With “timeout” in Bash

This example demonstrates a Bash script that waits for user input while providing a time limit for response. The script allows users to terminate the program by pressing any key on the keyboard within a 5-second period. Here’s a bash script to wait for input with timeout:

#!/bin/bash

echo "Press any key within 5 seconds"

# Loop until a key is pressed or 5 seconds have elapsed
while true; do
read -t 5 -n 1 key  # Read a single character within a 5-second
if [ $? = 0 ]; then
echo -e "\n$key is pressed. Program Terminated"
exit  # Exit the script if a key is pressed
else
echo "Waiting for a keypress"
fi
done

Here, q is pressed within 5 seconds. So, the program terminates. In this case, the program waits for an initial 5 seconds during which the user doesn’t press any key. So, it starts waiting for another 5 seconds. This time the user pressed n, hence the program terminated.

2. Wait for Pressing Any Key in Bash script

This example discusses a Bash script that waits for user input and terminates only when the user types any key in the keyboard. Open a file named anykey.sh & write the following script in the file to wait for user input:

#!/bin/bash

echo "Press any key to terminate the application..."

# Loop until a key is pressed
while true; do
read -rsn1 key  # Read a single character silently
if [[ -n "$key" ]]; then
echo "One key detected. Program terminated."
break  # Exit the loop if a key is pressed
fi
done

The program terminates as soon as a key is pressed. Note that it doesn’t include Enter key as the exit status of the return key is zero.

3. Wait for Pressing Specific Key in Bash script

Like waiting to press any key, we can write a Bash script that waits for specific input from the user. For instance, the script of this example terminates its execution only when the user presses q. Open a file named specifickey.sh & write the following script to wait for specific user input:

#!/bin/bash
echo "Press the 'q' key to quit..."
while true; do
  # Read a single character from the input
  read -n 1 key
  # Check if the pressed key is 'q'
  if [[ $key == "q" ]]; then
    echo -e "\nProgram is Quitting..."
    break
  else
    echo -e "\nPlease press q to exit."
  fi
done

The program prints Please press q to exit when f is pressed. But it works fine and terminates immediately as soon as q is pressed.

4. Wait for Inputting Specific Key with “timeout” in Bash

This example discusses how we can terminate the execution of a script within a time limit. The program waits for the user to input a specific key to terminate the execution. However, if the user is reluctant to terminate the program inputting that specific key it deliberately terminates itself automatically.

Check the bash script to wait for inputting specific key with timeout:

#!/bin/bash

echo "Program will terminate automatically after 5 seconds."
echo "Press Enter to terminate immediately."
read -t 5
read_exit_status=$?

if [ $read_exit_status = 0 ]; then
echo "You pressed Enter. Program terminated."
else
echo "Timeout occurred. Enter key was not pressed."
fi

The image shows that the program was run two times consecutively. First time it terminates automatically after 5 seconds though the user doesn’t press enter. Second time the user terminated the program by pressing enter before reaching 5 seconds timeout.

2 Practical Applications of Waiting for User Input Using Bash Script

Bash waits for user input and has many real-life applications. This article delves into the creation of interactive menus and the implementation of user confirmation before executing critical actions.  Waiting for user input is the central part of the execution of these applications.

1. Creating Interactive Menu Using Bash Script

In this application, we utilize Bash to create a restaurant menu that waits for user input. Users are presented with four different food items and have the option to select a menu item from the available choices. Here’s a bash code to create an interactive menu to wait for user input:

#!/bin/bash

echo "Program will terminate automatically after 5 seconds."
echo "Press Enter to terminate immediately."
read -t 5
read_exit_status=$?

if [ $read_exit_status = 0 ]; then
echo "You pressed Enter. Program terminated."
else
echo "Timeout occurred. Enter key was not pressed."
fi

Here, user select option A, so the program terminates echoing a message “You selected Pizza. Enjoy your meal !” This time user presses q, which is an invalid option. So the program prompts the options again and waits for taking valid input.

2. User Confirmation Before Critical Action in Bash Script

User confirmation is crucial for major tasks. It adds an extra layer of protection, ensuring users can prevent unintended consequences. For example, before installing potentially risky applications, obtaining user confirmation helps to avoid potential harm to the system and data.

In this Bash script, we create a program that takes user confirmation before deleting all the empty files of the current directory. Open a file & write the following script to accomplish this task:

#!/bin/bash

echo "This script will delete all empty files in the current directory. Are you sure you want to proceed? (y/n)"

while true; do
read -s -n 1 key

case $key in
y|Y)
echo "Deleting empty files..."
find . -type f -empty -print -delete
echo "You pressed $key. Empty files deleted successfully."
exit 0
;;

n|N)
echo "You pressed $key. Operation canceled."
exit 0
;;
*)
echo "Invalid input. Please press 'y' or 'n'."
;;
esac

done

This image shows the user enter n. So, the program executes the case statement and cancels the operation of deleting all empty files of the current directory.This time user press neither ‘y’ nor ‘n’. Hence it shows a message of invalid input and waits for the user input again.Finally, user press ‘y’. So the program proceeds and delete all the empty files from the current directory.

Conclusion

In conclusion, waiting for input in Bash scripts has many practical applications. In some cases, it is important to take input from the user for further execution of the script. Even it may be crucial to continue if the user delays giving input. Hope this article helps you to understand all the basics of implementing how to wait for input in Bash.

People Also Ask

How to pause execution and wait for user input?

The read command can be used to pause execution and wait for user input. -t option of read command is useful to pause a script. -t by default takes second as unit of timeout. The sleep command can also be used for similar purposes.

Wait for complete a background process or user input to terminate?

To terminate a background process based on user input kill command can be used. The read command can take user input. By detecting the input the kill command can terminate the background process.

How to exit if nothing is given in the input wait part?

The easy way to exit if nothing is given in the user input part is by adding a exit statement just after the input section.

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• How to Read CSV Files in Bash? [2 Methods]

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