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Subject: |
Re: Interaction of the -I and -L options of xargs |
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Date: |
Mon, 20 Jun 2005 12:17:07 +0100 |
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Mutt/1.5.9i |
James Youngman <address@hidden> wrote, on 19 Jun 2005:
>
> The functionality of the -L and -I (uppercase i) options by themselves
> is quite clear. However, how should they work in combination?
> Specifically, what should the output of this be?
>
> # Create a file containing the numbers 1 to 10, one per line
> ( while echo yes ; do true; done ) |sed -n -e '=' -e '10 q' > short-file.txt
>
> # This is the test of interest
> xargs -L 5 -I Z echo foo Z bar < short-file.txt
I think a formal interpretation would have to say that the standard
is unclear and no conformance distinction can be made.
> Should xargs produce (my indentation)
>
> foo 1 bar
> foo 2 bar
> foo 3 bar
> foo 4 bar
> foo 5 bar
> foo 6 bar
> foo 7 bar
> foo 8 bar
> foo 9 bar
> foo 10 bar
>
> or should it produce
>
> foo 1 2 3 4 5 bar
> foo 6 7 8 9 10 bar
>
> ... or, should this depend on the order in which -L and -I are
> specified on the command line (ugh)?
You say "ugh", but that is exactly how the standard specifies that
the conflict between -L and -n is handled ("The -L and -n options are
mutually-exclusive; the last one specified shall take effect.").
> IRIX and GNU findutils (as at version 4.2.23) produce the former while
> *BSD produces the latter. I'm at home today so don't have any other
> systems handy for testing.
Solaris, HP-UX and Unixware all produce the former. However, if
you switch the order (i.e. xargs -I Z -L 5 echo foo Z bar) they
all produce:
foo Z bar 1 2 3 4 5
foo Z bar 6 7 8 9 10
as does GNU findutils (4.2.21). I.e. the -L causes the earlier -I
to be ignored.
So it is looking like the appropriate way to handle this in the
next revision would be to have -L and -I cancel each other out, the
same as -L and -n do. Actually, all three conflict with each other,
so the standard should probably say "The -I, -L and -n options are
all mutually-exclusive; the last one specified shall take effect."
--
Geoff Clare <address@hidden>
The Open Group, Thames Tower, Station Road, Reading, RG1 1LX, England
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