8.6.15 Extract differences and merge updates for source files

Following one of these procedures will extract differences between two source files and create unified diff files file.patch0 or file.patch1 depending on the file location:

     $ diff -u file.old file.new1 > file.patch0
     $ diff -u old/file new1/file > file.patch1

The diff file (alternatively called patch file) is used to send a program update. The receiving party will apply this update to another file by:

     $ patch -p0 file < file.patch0
     $ patch -p1 file < file.patch1

If you have three versions of source code, you can merge them more effectively using diff3:

     $ diff3 -m file.mine file.old file.yours > file