Matthew Nuzum wrote:
>
> Can anyone point to clear instructions on how to use diff, especially in
> understanding and using the output?
The only form of diff I use is -u. This is called a unified diff. Here is
an example of it's output, explained. For this I used the -ruN options
(recursive, unified, new-files as diffs). Sometimes the -b option is
useful to ignore blankspace diffs.
> diff -ruN dist-2.4.12+patches/Documentation/Configure.help
>cvs-2.4.12+patches/Documentation/Configure.help
the command line - when diffing multiple files, diff puts this in.
> --- dist-2.4.12+patches/Documentation/Configure.help Mon Oct 15 10:20:16 2001
> +++ cvs-2.4.12+patches/Documentation/Configure.help Mon Oct 15 10:34:55 2001
The --- line shows the name of the old file.
The +++ line shows the name of the new file.
All lines that start with a - have been removed. All lines that start with
a + have been added. In non-unified diffs, sometimes you'll see other
line-markers.
> @@ -14952,9 +15177,10 @@
This is the hunk-header. It says that the hunk starts at line 14952 and
lasts 9 lines in the original file. It also says that the new hunk starts
at line 15177 in teh new file, and contains 10 lines. A net gain of one
line.
> CONFIG_NVRAM
> If you say Y here and create a character special file /dev/nvram
> with major number 10 and minor number 144 using mknod ("man mknod"),
This is context. By default diff uses 3 lines of context (a cmdline opt
can change that). This helps patch find where to put a diff when teh line
numbers don't match exactly. Always three lines at the top of a hunk and
three lines at the bottom. Thus, no hunk is less than 7 lines (6 context,
at least one change).
> - you get read and write access to the 50 bytes of non-volatile memory
> + you get read and write access to the extra bytes of non-volatile memory
This shows that the line changed, the old form is removed and the new form
is inserted at the same place
> in the real time clock (RTC), which is contained in every PC and
an unchanged line, but less than 3 lines, so no need for a new hunk.
> - most Ataris.
> + most Ataris. The actual number of bytes varies, depending on the
> + nvram in the system, but is usually 114.
This shows that one line was removed and two inserted. Here is our net
gain of one line.
>
> This memory is conventionally called "CMOS RAM" on PCs and "NVRAM"
> on Ataris. /dev/nvram may be used to view settings there, or to
3 lines of context at the end. So we have 3 context, 1 change, 1
unchanged, 1 change, 1 new, and 3 context = 10 lines.
> diff -ruN dist-2.4.12+patches/drivers/char/nvram.c
>cvs-2.4.12+patches/drivers/char/nvram.c
> --- dist-2.4.12+patches/drivers/char/nvram.c Mon Oct 15 10:21:41 2001
> +++ cvs-2.4.12+patches/drivers/char/nvram.c Mon Oct 15 10:21:41 2001
Another file.
> @@ -10,8 +10,9 @@
> * "NVRAM" (NV stands for non-volatile).
> *
> * The data are supplied as a (seekable) character device, /dev/nvram. The
> - * size of this file is 50, the number of freely available bytes in the memory
> - * (i.e., not used by the RTC itself).
> + * size of this file is dependant on the controller. The usual size is 50,
> + * the number of freely available bytes in the memory (i.e., not used by the
> + * RTC itself).
> *
> * Checksums over the NVRAM contents are managed by this driver. In case of a
> * bad checksum, reads and writes return -EIO. The checksum can be initialized
I'll leave the interpretation to you. Any file can have multiple hunks,
each starting with @@
Clear now? Maybe a bit :)
--
Tim Hockin
Systems Software Engineer
Sun Microsystems, Cobalt Server Appliances
[EMAIL PROTECTED]
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