Re: [bug-grep] [bug #12660] byte-offset has an off-by-one error

[Julian Foad]

anonymous wrote:
> URL:
>   <http://savannah.gnu.org/bugs/?func=detailitem&item_id=12660>
>
>                  Summary: byte-offset has an off-by-one error

Thanks for trying to help, but this is user error, not a bug.

>                  Project: grep
>             Submitted by: None
>             Submitted on: Tue 04/12/2005 at 14:22

[...]
> the byte offset reported when using the -b option is incorrect.  It is off by
> one *per line*.  (except of course the first line, which correctly reports 0
> offset).  So the byte offset reported on the Nth line is incorrect by (N-1). 
>
>
> I reproduced this with grep v2.5 on a Solaris system and grep v2.5.1 on a
> Linux system.  
>
> This can be easily demonstrated.  
> 1.  create a small file.  e.g.  
>     echo '0123456789abcdefghijklmnopqrstuv' > foo
>     foo will now contain 32 bytes (including the final cr) on a 
>     unix system.  (DOS will add a lf)

No, that's 32 printable characters, so 33 bytes including the final LF on a 
Unix system (and DOS will add a CR).

> 2.  view foo with xxd to satisfy self that this is true.  
>     use 'xxd -c 8 foo' - this will show four rows of 16

16 whats?  You mean 16 hexadecimal digits, plus the other information that it 
shows.  And it shows a fifth row showing the final LF byte:

0000000: 3031 3233 3435 3637  01234567
0000008: 3839 6162 6364 6566  89abcdef
0000010: 6768 696a 6b6c 6d6e  ghijklmn
0000018: 6f70 7172 7374 7576  opqrstuv
0000020: 0a                   .

>     (xxd will display 2 characters per byte)
> 3.  view output of 'xxd -p -c 8 foo' -- satisfy self that this 
>     outputs only the contents of the file in rows of 16 chars

It outputs this:

3031323334353637
3839616263646566
6768696a6b6c6d6e
6f70717273747576
0a

which is four rows each of sixteen printable characters plus one LF character, 
and one row of two printable characters plus one LF character.

> 4.  pipe it to grep as follows:
>     'xxd -p -c 8 foo | grep -b ".*"'   
> 5.  view output - note that although there are only 16 
>     chars per line,  grep reports offsets of 
>     0,17,34,51 ...

No, there are 17 characters per line including the LF, so the output is correct.

I have closed this bug as invalid.

Please discuss problems on this mailing list before filing a bug in the tracker.

- Julian