为什么'；svn diff--diff cmd=diff'；输出内部差异格式？

当我设置

--diff cmd=diff

时，我发现diff输出很奇怪

➜  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

我认为上面的两个命令本质上是如下的，我错了吗

➜  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

---

我从svn help diff

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

subversion会将默认参数
-u
传递给外部差异程序

➜  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

Subversion将以下参数传递给外部diff命令：


-u
或用户通过
-x>指定的标志。如果
-x
为空，则仍会传递
-u`
-L
基本标题
-L
工作副本标题
基本文件
工作副本文件

摆脱
-u
的唯一方法是传入另一个参数。我编写了一个Perl脚本，用于进行解析，然后将VIM用于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;