How To Enter Password Only Once in a Bash Script Needing Sudo

In this article, we will explore how to write a Bash script that requires sudo privileges, but only asks for the password once. This can be useful in automating tasks that require elevated privileges without compromising security.

Understanding Sudo and Bash Scripting

Before we dive into the solution, let’s briefly understand what sudo and Bash scripting are. Sudo is a powerful command in Linux that allows users to run programs with the security privileges of another user (normally the superuser, or root).

Bash scripting, on the other hand, is a way to automate the execution of commands in the Bash shell. Bash scripts are text files containing a series of commands. These scripts can run complex and repetitive tasks automatically, saving time and reducing the chance of human error.

The Challenge

When a Bash script includes a command that requires sudo privileges, the script will normally pause and ask the user to enter their password. This can be a problem if you want to run the script unattended or automate it with a cron job.

The challenge, therefore, is to write a Bash script that only asks for the sudo password once, even if it includes multiple commands that require sudo privileges.

The Solution

To overcome this challenge, we can use a combination of the read, printf, and sudo commands in our Bash script. Here is a step-by-step guide on how to do this:

Step 1: Check If The Script Is Being Run As Root

First, we need to check if the script is being run as root. We can do this by using the $EUID variable, which holds the effective user ID of the current user. If the script is not being run as root, we display an error message and exit the script. Here’s how to do this:

#!/bin/bash

# Check if script is being run as root
if [[ $EUID -ne 0 ]]; then
 echo "This script must be run as root, use sudo "$0" instead" 1>&2
 exit 1
fi

In this code snippet, [[ $EUID -ne 0 ]] checks if the effective user ID is not equal to 0 (the user ID of the root user). If this condition is true, the script prints an error message and exits.

Step 2: Prompt User for Password

Next, we prompt the user for the password using the read command and store it in a variable:

# Prompt user for password
read -p "Password: " -s szPassword

In this command, -p allows us to specify a prompt, and -s makes the input silent, so the password is not displayed when the user types it.

Step 3: Use Sudo and Printf to Pass the Password

Finally, we use printf to pass the password to sudo and the command that requires sudo privileges:

# Use sudo and printf to pass the password to the command
printf "%s\n" "$szPassword" | sudo -S command

In this command, printf "%s\n" "$szPassword" formats the password as a string followed by a newline character. The pipe (|) passes this string to sudo -S command, where -S tells sudo to read the password from the standard input.

Wrapping Up

This approach allows us to write a Bash script that only asks for the sudo password once, even if it includes multiple commands that require sudo privileges. However, it’s important to note that this method should be used carefully, as it can pose a security risk if the script is not properly secured.

Here’s the complete script:

#!/bin/bash

# Check if script is being run as root
if [[ $EUID -ne 0 ]]; then
 echo "This script must be run as root, use sudo "$0" instead" 1>&2
 exit 1
fi

# Prompt user for password
read -p "Password: " -s szPassword
echo

# Use sudo and printf to pass the password to the command
printf "%s\n" "$szPassword" | sudo -S command

Remember to replace command with the command you want to run with sudo privileges.

For more information on sudo, read, and printf, you can check their man pages by typing man sudo, man read, and man printf in the terminal, respectively.

I hope this article was helpful and informative. Happy scripting!