cd demo

有bug文件a.txt：

当前目录为demo

mkdir -p  old/a/p

vi   old/a/p/foo.txt

old_line_1

old_line_2

bug 修复后的foo.txt：

当前目录为demo

mkdir -p  new/a/p

vi   new/a/p/foo.txt

new_line_1

new_line_2

补丁产生:

当前目录为demo

LC_ALL=C TZ=UTC0 diff -Naur old new > foo.patch

补丁内容：
当前目录为demo

[root@monitor demo]# cat foo.patch
diff -Naur old/a/b/foo.txt new/a/b/foo.txt

--- old/a/b/foo.txt     -- ::56.999206666 +

+++ new/a/b/foo.txt     -- ::03.160497528 +

@@ -, +, @@

-old_line_1

-old_line_2

+new_line_1

+new_line_2

模拟打补丁：(补丁针对 old/a/b.foo.txt文件打补丁）
当前目录demo

[root@monitor demo]# patch -p0 <foo.patch

 patching file old/a/b/foo.txt

当前目录demo

[root@monitor demo]# mkdir xx
[root@monitor demo]# cp foo.patch xx
[root@monitor demo]# patch -p0 < xx/foo.patch
 patching file old/a/b/foo.txt

cd xx

当前目录为demo/xx

[root@monitor xx]# patch -p0 < foo.patch

can't find file to patch at input line 4
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|diff -Naur old/a/b/foo.txt new/a/b/foo.txt
|--- old/a/b/foo.txt 2016-05-26 06:57:56.999206666 +0000
|+++ new/a/b/foo.txt 2016-05-26 06:59:03.160497528 +0000

说明在当前目录不能找到  old/a/b/foo.txt (在demo/xx目录下找到文件与目录去补丁

P0:你当前的目录位置,去找old/a/b/foo.txt

p1:你当前目录位置去找a/b/foo.txt,p1会掉old/,到当前目录找a/b/foo.txt

p2:你当前目录位置去找a/b/foo.txt,p2会掉old/a,到当前目录找b/foo.txt

p3:你当前目录位置去找a/b/foo.txt,p3会掉old/a/b,到当前目录找foo.txt

结论：决定补丁如何补:你的补丁所在的目录（你该把补丁放在那里)
     P(N)决定去查找要补丁的文件路径,不同的N,会掉某部分路径后,再在当前目录,找已除掉后路径,找文件去补丁
     P(N)与当前目录关系很大,与补丁在那里没有关系

    patch -d xx  P(N) 〈 XX  可以命令行上指定 工作目录