[Work Notes] Patch Files in Linux

Creating a Patch File

diff -Naur old-dir-or-file new-dir-or-file > patchfile.patch

How to Apply a Patch

There are two common ways to apply a patch:

# Method 1
cat new-patch | patch -p0

# Method 2
patch -p0 < new-patch

Understanding the -p (strip) Parameter

The -p parameter specifies how many leading directory components to strip from paths in the patch file.

For example, if a patch file begins with:

--- old/modules/network  JAN 26 12:11:36 2002
+++ new/modules/network  SEP 20 20:07:38 2003

• -p0: Start from the current directory and look for the full path old/modules/network
• -p1: Strip the first directory level (old or new), then look for modules/network from the current directory

Patch File Structure

• Lines beginning with --- and +++ indicate the files to be patched.
• A single patch file can contain multiple patches — each patch is a separate ---/+++ block.
• Each block (hunk) represents a section to be modified, typically surrounded by unchanged context lines for location reference.
• Hunks begin with @@ and end at the start of another hunk or a new patch header.
• Hunk indentation:
  • + at the start of a line: this line is to be added
  • - at the start of a line: this line is to be deleted