diff - AIX diff -b 坏了？

Question

我正在尝试比较忽略回车符的文件 - diff -b 在任何其他 unix 上的表现令人钦佩。但是在这个 AIX 5.3 机器上:

    tst1:tst2$ od -c testfile
0000000    t   h   i   s  \r  \n   f   i   l   e  \r  \n   h   a   s  \r
0000020   \n   c   a   r   r   i   a   g   e  \r  \n   r   e   t   u   r
0000040    n   s  \r  \n
0000044
tst1:tst2$ od -c testfile_nocr
0000000    t   h   i   s  \n   f   i   l   e  \n   h   a   s  \n   c   a
0000020    r   r   i   a   g   e  \n   r   e   t   u   r   n   s  \n
0000037
tst1:tst2$ diff -b testfile testfile_nocr
1,5c1,5
< this
< file
< has
< carriage
< returns
---
> this
> file
> has
> carriage
> returns
tst1:tst2$

为什么这样？

Answer 1

AIX 5.3 diff 似乎没有考虑 \r作为空白。请参阅以下成绩单:

/home/pax: od -c file1
0000000    h   e   l   l   o  \n   t   h   e   r   e  \n
0000014

/home/pax: od -c file2
0000000    h   e   l   l   o  \r  \n   t   h   e   r   e  \r \n
0000016

/home/pax: od -c file3
0000000    h   e   l   l   o      \n   t   h   e   r   e     \n
0000016

/home/pax: od -c file4
0000000    h   e   l   l   o  \t  \n   t   h   e   r   e  \t \n
0000016

/home/pax: diff -b file1 file2
1,2c1,2
< hello
< there
---
> hello
> there

/home/pax: diff -b file1 file3
<<No output>>

/home/pax: diff -b file1 file4
<<No output>>

diff 的联机帮助页在这件事上有点迟钝，说 -b将“导致行尾的任意数量的空白被视为单个换行符......”但实际上并没有定义它认为是空白的内容。

根据上述成绩单，我认为空格和制表符可以，但回车不行。

解决此问题的一种方法是使用如下脚本自行删除回车符:

#!/usr/bin/ksh
# crdiff: diffs two files after changing \r\n to \n in both.
if [[ $# -ne 2 ]] ; then
    echo 'Usage: crdiff <file> <file2>'
    return 1
fi
perl -pne 's/\r$//' $1 >/tmp/xyzzy_$$_$1
perl -pne 's/\r$//' $2 >/tmp/xyzzy_$$_$2
diff -b /tmp/xyzzy_$$_$1 /tmp/xyzzy_$$_$2
rc=$?
rm -f /tmp/xyzzy_$$_$1 /tmp/xyzzy_$$_$2
return $rc

或者，您可以编译 GNU diff实用程序，并将其插入 /usr/bin 之前的路径中- 似乎没有问题 \r作为空白。事实上，自 diff 起，我们在 AIX4 机器上就是这样做的。甚至不假装支持 -b选项。