Re: [coreutils] cut feature request

[Eric Blake]

On 09/07/2010 10:29 AM, Laurent Lyaudet wrote:
> Hi,
> it would be useful that cut handles negative numbers parameters for
> columns and fields as "from the end" parameters.
> One could select the last field with -f -1 for example. (Currently, -f
> -1 do the same that -f 1.)

Thanks for the report.  I also wonder if allowing negative end fields 
for sort -k key specifiers also makes sense.

> I didn't find a previous request that is similar in coreutils archive.
> I think using awk or something similar is overkill for solving that
> problem.

On the contrary, we tend to take the conservative position that if there 
is a POSIX-mandated tool that already does what you need, then adding an 
alternative shortcut to some other tool to do the same thing is very 
difficult to justify, on the grounds that you cannot rely on our 
extension, but can rely on awk's behavior, when porting to multiple 
systems.  In other words, the bar for 'convenience' features is rather 
high before considering additions like this.

It may help us decide by showing a sample input file and a command line 
using your proposed extension, along with any awk alternative to do the 
same, to convince us that the verbosity required in awk is worth such a 
shortcut (or conversely, that the awk script is already so simple as to 
not be worth changing cut, as has already been our argument for the 
numerous times that people suggest teaching cut how to reorder fields).

> Let me know what you think about it.

If we do it, I'd like to see it done uniformly across all the coreutils 
that take partial field specifications.  And although I probably won't 
be the one writing such a patch, it does sound like it still might be 
justifiable.

--
Eric Blake   address@hidden    +1-801-349-2682
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