How To Retrieve User Input from Dialog Box in Bash Scripting

In the world of scripting, it is often necessary to interact with users and retrieve their input. Bash scripting is no different. This article will guide you on how to retrieve user input from a dialog box in Bash scripting, with a focus on the dialog command and its application.

Introduction to Dialog Boxes in Bash

A dialog box is a small window that prompts the user to enter data. It is a user-friendly way of getting input in a graphical user interface (GUI). However, in the context of Bash scripting, we are dealing with a command-line interface (CLI), not a GUI. This is where the dialog command comes into play.

The dialog command allows you to display dialog boxes from shell scripts. It supports various types of dialog boxes, including input boxes, message boxes, yes/no boxes, and more. The dialog command is not installed by default on all systems, so you may need to install it using a package manager like apt, yum, or dnf.

Using Dialog to Retrieve User Input

Here is a simple example of how to use the dialog command to retrieve user input:

#!/bin/bash
input=$(dialog --inputbox "What is your username?" 0 0 2>&1 >/dev/tty)
retval=$?

case $retval in
0)
 echo "Your username is '$input'";;
1)
 echo "Cancel pressed.";;
esac

Let’s break down this script:

• #!/bin/bash: This is the shebang line that specifies the script should be executed using the Bash shell.
• input=$(dialog --inputbox "What is your username?" 0 0 2>&1 >/dev/tty): This line uses the dialog command to display an input box with the message “What is your username?”. The 0 0 parameters specify the height and width of the dialog box, respectively. If these are set to 0, the dialog box will automatically adjust to the size of the message. The 2>&1 >/dev/tty redirection sends the output of the dialog command (which is on STDERR) to STDOUT and then redirects it to the terminal (/dev/tty). The $(...) syntax captures the output of the command and assigns it to the input variable.
• retval=$?: This line captures the exit status of the last executed command, which in this case is the dialog command. The exit status is 0 if the user pressed OK, and 1 if the user pressed Cancel.
• The case statement checks the value of retval and performs different actions based on the result. If the exit status is 0, it echoes the user’s input. If the exit status is 1, it echoes “Cancel pressed.”

Alternative Approaches

While the dialog command is a powerful tool for creating dialog boxes in Bash scripts, there are other methods you can use to achieve the same result.

Using a Temporary File

You can use a temporary file to capture the user’s input. Here’s how:

#!/bin/bash
tempfile=$(mktemp)
dialog --inputbox "What is your username?" 0 0 2> $tempfile
input=$(cat $tempfile)
rm -f $tempfile

echo "Your username is '$input'"

In this script, the mktemp command creates a temporary file, and the dialog command redirects its output to this file. The cat command reads the contents of the file into the input variable, and the rm -f command removes the temporary file.

Using Zenity

Zenity is a tool that allows you to display GTK+ dialog boxes from command line scripts. It provides a more graphical alternative to dialog but requires an X server.

#!/bin/bash
input=$(zenity --entry --text "What is your username?")
echo "Your username is '$input'"

In this script, the zenity --entry command displays an input dialog box, and the $(...) syntax captures the output into the input variable.

Conclusion

Retrieving user input from a dialog box in Bash scripting can be achieved in a number of ways, with the dialog command being one of the most commonly used methods. By understanding how to use this command and its parameters, you can create interactive scripts that prompt users for input in a user-friendly manner. Remember to always consider your specific needs and the environment in which your script will run when choosing the method to use.