Why 'svn diff --diff-cmd=diff ' output inner diff format?

Question

I found diff output is strange when I set --diff-cmd=diff.

➜  svntest  svn diff --diff-cmd=diff -x '' #The cmd `diff` cann't output this format, so strange 
Index: a.c
===================================================================
--- a.c (revision 1)
+++ a.c (working copy)
@@ -0,0 +1 @@
+teste

➜  svntest  svn diff --diff-cmd=diff -x '-i'
Index: a.c
===================================================================
0a1
> teste

I thought the two commands above essentially excute as below, am I wrong?

➜  svntest  diff   -L 'a.c(revision 1)' -L 'a.c(working copy)' '/Users/hilojack/www/svntest/.svn/pristine/da/da39a3ee5e6b4b0d3255bfef95601890afd80709.svn-base' '/Users/hilojack/www/svntest/a.c'
0a1
> teste
➜  svntest  diff  -i -L 'a.c(revision 1)' -L 'a.c(working copy)' '/Users/hilojack/www/svntest/.svn/pristine/da/da39a3ee5e6b4b0d3255bfef95601890afd80709.svn-base' '/Users/hilojack/www/svntest/a.c'
0a1
> teste

I get this from svn help diff

-x [--extensions] ARG    : Default: '-u'. When Subversion is invoking an external diff program, ARG is simply passed along to the program.

The subversion will pass default params -u to external diff program.

➜  svntest  svn diff --diff-cmd=echo
Index: a.c
===================================================================
-u -L a.c   (revision 1) -L a.c (working copy) /Users/hilojack/www/svntest/.svn/pristine/da/da39a3ee5e6b4b0d3255bfef95601890afd80709.svn-base /Users/hilojack/www/svntest/a.c

Thanks for posting this. I can't understand how this output is useful for a custom diff command. — Sridhar Sarnobat
– Sridhar Sarnobat, Commented Jun 4, 2024 at 20:03

David W. · Accepted Answer · 2014-05-09 17:56:49Z

4

Subversion passes the following parameters to the external diff command:

-u or the user specified flags via -x'. If-xis null, the-u` is passed anyway.
-L
Base Title
-L
Working Copy Title
Base file
Working copy file

The only way to get rid of -u is to pass in another parameter. I wrote a Perl script I use to do my parsing and then use VIM for my diff:

#! /usr/bin/env perl

use strict;
use warnings;

use constant DIFF => qw(mvim -d -f);

my $parameters = $#ARGV;
my $file1 = $ARGV[$parameters - 1];
my $file2 = $ARGV[$parameters];
my $title1 = $ARGV[$parameters - 4];
my $title2 = $ARGV[$parameters - 2];

$ENV{TITLE} = "$title1  -   $title2";
system DIFF, '-c', 'let &titlestring=$TITLE', $file1, $file2;

answered May 9, 2014 at 17:56

David W.

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Sridhar Sarnobat · Accepted Answer · 2024-06-04 20:27:34Z

Diffmerge Command Line options

This doesn't answer the question but I hope will be useful background for people who land on this page, and doesn't seem to be on the official site (https://sourcegear.com/diffmerge/webhelp/chapter_clargs.html).

Mac

    SourceGear DiffMerge - Version 4.1.0 (534:eca1777d85) [intel] stable
    Copyright (C) 2003-2013 SourceGear LLC. All Rights Reserved.

    Synopsis:
    DiffMerge [options] [path1 [path2 [path3]]]

    Options:
    -h, -help, --help
    -c=STRING, -caption=STRING, --caption=STRING
    -m, -merge, --merge
    -r=PATH, -result=PATH, --result=PATH
    -ro2, --ro2
    -t1=STRING, -title1=STRING, --title1=STRING
    -t2=STRING, -title2=STRING, --title2=STRING
    -t3=STRING, -title3=STRING, --title3=STRING
    -nosplash, --nosplash

    Batch Options:
    -d=PATH, -diff=PATH, --diff=PATH
    -u, -unified, --unified

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