Re: Bug in 'tail' (coreutils 6.10) -- '+' option not working

[Eric Blake]

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According to Joshua White on 9/20/2009 9:46 AM:
> The '+' option appears not to be working as documented.  From the man page:
> "If the first character of N (the number of bytes or lines) is a ‘+’, print
> beginning with the Nth item from the start of each file, otherwise,  print
> the last N items in the file."  I recall this working in previous versions.

Not a bug, but a difference in various versions of POSIX.  From the NEWS file:

>  A few usages still have behavior that depends on which POSIX standard is
>   being conformed to, and portable applications should beware these
>   problematic usages.  These include:
> 
>     Problematic       Standard-conforming replacement, depending on
>        usage            whether you prefer the behavior of:
>                       POSIX 1003.2-1992    POSIX 1003.1-2001
>     sort +4           sort -k 5            sort ./+4
>     tail +4           tail -n +4           tail ./+4
>     tail - f          tail f               [see (*) below]
>     tail -c 4         tail -c 10 ./4       tail -c4
>     touch 12312359 f  touch -t 12312359 f  touch ./12312359 f
>     uniq +4           uniq -s 4            uniq ./+4
> 
>     (*) "tail - f" does not conform to POSIX 1003.1-2001; to read
>     standard input and then "f", use the command "tail -- - f".

You can also change behavior on the fly; read 'info coreutils standards',
which states:

>    The GNU utilities normally conform to the version of POSIX that is
> standard for your system.  To cause them to conform to a different
> version of POSIX, define the `_POSIX2_VERSION' environment variable to
> a value of the form YYYYMM specifying the year and month the standard
> was adopted.  Two values are currently supported for `_POSIX2_VERSION':
> `199209' stands for POSIX 1003.2-1992, and `200112' stands for POSIX
> 1003.1-2001.  For example, if you have a newer system but are running
> software that assumes an older version of POSIX and uses `sort +1' or
> `tail +10', you can work around any compatibility problems by setting
> `_POSIX2_VERSION=199209' in your environment.


> tail (GNU coreutils) 6.10

Consider upgrading; the latest stable version is 7.6, and has some fixes
in tail.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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