Re: [coreutils] "cut" from last column

[Brian Dessent]

Philip Ganchev wrote:

> > > cut -f 3,5-+3 myfile
> >
> > How about:
> >
> > perl -F'\t' -nae 'print join "\t", @F[2,4..$#F-3]' myfile
> 
> Even more verbose and complicated (clumsy).

Your original cut example requires forking four external binaries and
one shell builtin, and involves at least two subshells.  To me, that is
a lot more complicated (in terms of both syscalls and points of failure)
than just running a single perl (or awk) command with no subshells.

> Plus, it depends on
> having Perl, which is not a coreutil as far as I know.

You're asking for a feature that currently does not exist in 'cut' to be
added.  Do you realize how long it will take before you could count on
being able to use this feature in a portable script?  Even if the
feature was added today I bet that you would find many systems in three
years from now that are still running an out of date coreutils that
would not support that feature.  Just look at all the people that post
to this list that are still using coreutils 5.2x or even its
predecessors, textutils/fileutils/sh-utils.  And on systems that use the
vendor 'cut' instead of GNU 'cut', the feature will essentially never be
available.

On the other hand, a unix-like system that is not an embedded device
that does not have perl (or awk) installed is pretty rare.  So if the
question is availability or portability of a particular feature, to me
it looks like there is no contest.

> going to use Perl, why do we need "cut" at all?  It is just sensical
> that if a command allows you to cut from the beginning, it will let
> you cut from the end.

I agree that it sounds like a logical idea, but the problem comes when
you try to add features to programs like 'cut' that have existed for
probably decades and that are standardized by IEEE/POSIX, and have
multiple implementations (i.e. not everybody uses GNU cut.)  Any
features you add become GNU extensions, and can't be used in anything
but private scripts that you don't ever intend to distribute to anyone
since there's a very low chance they will work on other people's
systems.

Brian