Using Diff

metallica1973 · 12-04-2007, 07:10 AM

How can one compare the difference between 2 files and then redirect them to a file with the changes already applied? In other words compare the changes, make the changes and then write it to a file? thanks

druuna · 12-04-2007, 07:41 AM

Hi,

You want to make this an automated process? If so: You probably cannot do that.

How would the this automated process know which of the differences are correct?

I.e: File one holds (all on 1 line) 1 2 3 4, and file two holds (again all on one line) 1 2 3 5. Is 4 correct and 5 not correct, is 5 correct and 4 incorrect or are both correct.

Hope I understood correctly and if so I hope this clears things up a bit.

matthewg42 · 12-04-2007, 07:50 AM

Code:

$ cat file_one
this is file_one
hello world

$ cat file_two
this is file_two
hello world

$ diff -u file_one file_two | tee my.patch
--- file_one    2007-12-04 13:47:22.000000000 +0000
+++ file_two    2007-12-04 13:47:11.000000000 +0000
@@ -1,2 +1,2 @@
-this is file_one
+this is file_two
 hello world

$ patch < my.patch
patching file file_one

$ cat file_one
this is file_two
hello world

druuna · 12-04-2007, 07:56 AM

Hi,

@matthewg42: Ok, that works. But isn't it true that it only works if you know which file is correct and which one isn't?

matthewg42 · 12-04-2007, 08:16 AM

What do you mean?

druuna · 12-04-2007, 08:38 AM

Hi,

In your example file_one is the file that needs to be changed, file_two is the file that holds the correct data (the 'patch'). In that case your solution works.

If, in the example the OP gave, you have two files which are different, you cannot let an automated process determine which changes are correct (see also post #2).

matthewg42 · 12-04-2007, 10:13 AM

The OP didn't make much sense, and I took a little guess at the intention. It still doesn't make a lot of sense. Perhaps an example would help - can you provide one?

metallica1973 · 12-04-2007, 12:34 PM

Druuna and mathewg42 many thanks, also I love me some Druuna. She is one of favorite Fantasy Art characters.

druuna · 12-04-2007, 12:43 PM

Hi,

I'm still curious what the original problem was. matthewg42 and I both assumed and came up with answers that conflict. Anyway, glad to read that our input helped.

PS: Fantasy Art character??? She's alive in my reality

metallica1973 · 12-04-2007, 06:25 PM

I think that you can just use diff to do everything in one command!

matthewg42 · 12-05-2007, 01:14 AM

No, diff finds differences. Patch apples them (or ed if you tell diff to make ed-style patches).

Besides, if you have both files, and want to change file2 to be like file1, why not just copy file1 over file2?

The whole point of the diff/patch system is that you can send just the diff to someone who has a file which you have, and they can apply it without having to receive a copy of the whole new file (presumably saving bandwidth and time).

metallica1973 · 12-05-2007, 05:19 AM

no, what I am mean by my example is to compare two different files (file_one and file_two)for differences and remove the differences and them redirect that to a new single file. I hope I said that correctly.

druuna · 12-05-2007, 05:26 AM

Hi,

If you want the entries that are both in file_one and file_two and not the differences (in either):

comm -12 file_one file_two > file_three

Example:

Code:

$ cat file_1
1
2
3
4
$ cat file_2
1
2
3
5
$ comm -12 file_1 file_2
1
2
3

The comm command can be more flexible then the diff command. Take a look at both manpages.

Hope this helps.

matthewg42 · 12-05-2007, 05:52 AM

Quote:

Originally Posted by metallica1973

no, what I am mean by my example is to compare two different files (file_one and file_two)for differences and remove the differences and them redirect that to a new single file. I hope I said that correctly.

OK, even if this is not the command you're looking for, does it essentially do the same thing (this is a test to see if my understanding of the question is correct):

Code:

diff file_one file_two > my.diff
cp file_one file_two

Would you end up with the same results that you want using this method? If not, please try to explain again.

metallica1973 · 12-06-2007, 07:13 AM

PHP Code:


			
# cat test_data1

192.168.1.1

192.168.2.1

192.168.1.3

192.168.2.2

# cat test_data2

192.168.1.1

192.168.1.2

192.168.1.3

192.168.1.4

# diff test_data1 test_data2 > output

# cat output

2c2

< 192.168.2.1

---

> 192.168.1.2

4c4

< 192.168.2.2

---

> 192.168.1.4

This is what I want but without:

PHP Code:


			
192.168.2.1

192.168.1.2

192.168.2.2

192.168.1.4

Can diff do this in one command?