Re: sorting with -u and -k

[Paul Eggert]

Joost Helberg <address@hidden> writes:

> given options '-t: -k2 -k3' the following lines compare equal:
>
>   foo:1:2
>   oof:1:2
>
> hence, the oof-line doesn't appear in case -u was used.
>
> This strikes me as a surprise, I expected that these two lines would
> compare as non-equal. I cannot find any explicit reference in the
> manual indicating this as correct behaviour (only one example is
> given: -n).

Thanks for mentioning this.  Here's a proposed fix to the manual
to explain this more carefully.

2008-01-24  Paul Eggert  <address@hidden>

        * coreutils.texi (sort invocation): -u inspects only specified fields.
        Problem reported by Joost Helberg.

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 3785eae..3741e5d 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -3793,6 +3793,8 @@ this equivalence does not extend to arbitrary 
@command{sort} options.
 For example, @code{sort -n -u} inspects only the value of the initial
 numeric string when checking for uniqueness, whereas @code{sort -n |
 uniq} inspects the entire line.  @xref{uniq invocation}.
+Similarly, @code{sort -k 4,4 -u} inspects only the fourth field when
+determining whether two lines differ.

 @item -z
 @itemx --zero-terminated