It’s like when you buy a car but want some extra features added on instead of buying an entirely new model, you just get the upgrades installed.
So how does it work? Well, let’s say there’s this awesome program called “SuperCalc” that comes with Debian by default. But maybe you need to add a feature that isn’t included in the original version like being able to calculate pi to 10 decimal places instead of just two.
To do this, we can create a patch file (which is basically just a text document) and apply it to SuperCalc using dpkg-patch. This will add our new feature without messing up any other parts of the program or causing conflicts with other packages.
Here’s an example:
1. First, let’s say we want to create a patch file for adding pi calculations to 10 decimal places in SuperCalc. We can do this by opening up our favorite text editor (like Notepad on Windows or Leafpad on Linux) and creating a new document called “supercalc-pi-fix.patch”.
2. In the patch file, we’ll add some code that tells dpkg-patch what to change in SuperCalc. For example:

--- supercalc/calculate_numbers.py  (original) # Indicates the original file being modified
+++ supercalc/calculate_numbers.py    (modified) # Indicates the modified file
@@ -12,6 +12,7 @@
 # Calculates the sum of two numbers using a for loop
 def calculate_sum(x, y):
     total = 0 # Initializes the variable total to 0
+    pi = math.pi # Imports the pi constant from the math module
     for i in range(x, y+1): # Loops through the range of numbers from x to y+1
         total += i # Adds the current number to the total
         print("The value of pi is: {:.10f}".format(pi)) # Displays the current value of pi with 10 decimal places
     return total # Returns the final total of the sum of numbers

3. This patch file tells dpkg-patch that we want to replace lines 12 through 17 in “calculate_numbers.py” with our new code (which includes adding a variable called “pi” and printing out its current value).
4. Once the patch is created, we can apply it using dpkg-patch like this:

# This line uses sudo to run the dpkg-patch command with root privileges
sudo dpkg-patch -p < supercalc-pi-fix.patch > /dev/null 2>&1
# The -p flag specifies the path to the patch file we want to use
# The < symbol redirects the contents of the patch file to the dpkg-patch command
# The > symbol redirects the output of the command to /dev/null, a special device that discards all data written to it
# The 2>&1 redirects any error messages to the same place as the standard output, in this case /dev/null
# This ensures that any error messages are not displayed on the screen, keeping the output clean and concise.

This will tell dpkg-patch to use our new patch file and apply the changes without printing out any output (which is useful if we don’t want to see a bunch of messages on the screen).
5. After running this command, we can test SuperCalc by opening it up and seeing if pi calculations are now working correctly!
And that’s how you manage patches in Debian packages easy peasy lemon squeezy!