View source for Patch (utility)

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'''patch''' is a utility used to apply source code [[patch]]es to a source code tree. Source code patches are commonly used to distribute code changes to developers working on open-source projects.

The '''diff''' utility is used to create patches, which can then be applied by '''patch'''.

== Unified Diff ==
The most common format for patches is the unified diff. The unified diff shows both line additions and removals, which are indicated by '+' and '-' symbols at the front of each line, respectively.

Example unified diff:

 --- a/pyl.asm
 +++ b/pyl.asm
 @@ -55,9 +55,9 @@ START:
         jsr     draw_active_square
 
  main:
 -       ; Wait 16 frames. (1/3 second)
 -       ; TODO: Support PAL timing.
 -       moveq   #15, d0
 +       ; Wait a bit to advance the square.
 +       moveq   #0, d0
 +       move.b  RAM_Frames_SquareAdvance, d0
  .vsync_loop:
                 jsr     VSync
                 dbf     d0, .vsync_loop

In order to make a Unified Diff with the '''diff''' utility, simply use this example:

 '''diff -U''' ''old_source'' ''new_source''

where ''old_source'' is your unaltered disassembly and ''new_source'' is end result.  You will need to redirect the output to a file of some sort, possibly with a pipe or an external program on your system.

On the other hand, you can also apply these patches in this manner:

 '''patch -Np1 -i''' ''path_to_patch_file''

from the inside of the disassembly being patched.  The 1 assumes that the folder depth is 1.  If the patch was made with a larger folder depth, then simply count the number of /'s in the paths in the patch itself.  This will prevent errors down the rode and is a good reason to keep the folder depth to 1 in all patches, it makes life simpler for the rest of us.

== POSIX Diff ==
The '''diff''' utility can also run in POSIX mode and create a POSIX compliant Diff, which uses > and < instead of + and -. The '''patch''' utility also supports these.

Example posix diff:
 Binary files s1hive/alink.msg and s1hive-as/alink.msg differ
 Common subdirectories: s1hive/_anim and s1hive-as/_anim
 Binary files s1hive/as.msg and s1hive-as/as.msg differ
 Binary files s1hive/asw.exe and s1hive-as/asw.exe differ
 diff -P s1hive/build.bat s1hive-as/build.bat
 2c2
 < include.exe sonic1.asm s1comb.asm
 ---
 > REM include.exe sonic1.asm s1comb.asm
 13c13,15
 < snasm68k.exe -emax 0 -p -o ae- s1comb.asm, s1built.bin
 ---
 > cls
 > asw  -xx -c -A sonic1.asm
 > p2bin sonic1.p s1built.bin -l 0 -r $-$
 Binary files s1hive/cmdarg.msg and s1hive-as/cmdarg.msg differ
 Common subdirectories: s1hive/_dlls and s1hive-as/_dlls
 Common subdirectories: s1hive/_inc and s1hive-as/_inc


In order to make a POSIX Diff with the '''diff''' utility, simply use this example:

 '''diff -P''' ''old_source'' ''new_source''

where ''old_source'' is your unaltered disassembly and ''new_source'' is end result.  You will need to redirect the output to a file of some sort, possibly with a pipe or an external program on your system.

On the other hand, the '''patch''' utility can apply these in the exact same manner as with Unified Diffs.

== Reverse Patching ==
Sometimes you end up with a patch that does not agree with your hack and makes it defunct.  In that case you will want to apply a Reversed Patch to undo the changes.

Here is how you do that:

 '''patch -Np1 -R -i''' ''patch_in_question''

where ''patch_in_question'' is the patch you want to undo. 

== Downloads ==
* GNU patch: http://www.gnu.org/software/patch/
* GNU patch (Win32): http://gnuwin32.sourceforge.net/packages/patch.htm
* GNU diffutils: http://www.gnu.org/software/diffutils/
* GNU diffutils (Win32): http://gnuwin32.sourceforge.net/packages/diffutils.htm

[[Category:Programs]]