External diff

Subversion calls external diff programs with parameters suitable for the GNU diff utility, and expects only that the external program return with a successful error code. For most alternative diff programs, only the sixth and seventh arguments—the paths of the files which represent the left and right sides of the diff, respectively—are of interest. Note that Subversion runs the diff program once per modified file covered by the Subversion operation, so if your program runs in an asynchronous fashion (or “backgrounded”), you might have several instances of it all running simultaneously. Finally, Subversion expects that your program return an error code of 1 if your program detected differences, or 0 if it did not—any other error code is considered a fatal error. [50]

Example 7.2, “diffwrap.sh” and Example 7.3, “diffwrap.bat” are templates for external diff tool wrappers in the Bourne shell and Windows batch scripting languages, respectively.

Example 7.2. diffwrap.sh

#!/bin/sh

# Configure your favorite diff program here.
DIFF="/usr/local/bin/my-diff-tool"

# Subversion provides the paths we need as the sixth and seventh 
# parameters.
LEFT=${6}
RIGHT=${7}

# Call the diff command (change the following line to make sense for
# your merge program).
$DIFF --left $LEFT --right $RIGHT

# Return an errorcode of 0 if no differences were detected, 1 if some were.
# Any other errorcode will be treated as fatal.

Example 7.3. diffwrap.bat

@ECHO OFF

REM Configure your favorite diff program here.
SET DIFF="C:\Program Files\Funky Stuff\My Diff Tool.exe"

REM Subversion provides the paths we need as the sixth and seventh 
REM parameters.
SET LEFT=%6
SET RIGHT=%7

REM Call the diff command (change the following line to make sense for
REM your merge program).
%DIFF% --left %LEFT% --right %RIGHT%

REM Return an errorcode of 0 if no differences were detected, 1 if some were.
REM Any other errorcode will be treated as fatal.



[50] The GNU diff manual page puts it this way: “An exit status of 0 means no differences were found, 1 means some differences were found, and 2 means trouble.