[bug #52137] unexpected behaviour when combining -I and -n

[Ulrich Sibiller]

URL:
  <http://savannah.gnu.org/bugs/?52137>

                 Summary: unexpected behaviour when combining -I and -n
                 Project: findutils
            Submitted by: uli42
            Submitted on: Thu 28 Sep 2017 10:37:17 AM UTC
                Category: xargs
                Severity: 3 - Normal
              Item Group: Wrong result
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.5.11
           Fixed Release: None

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Details:

I see an unexpected behaviour with xargs on Ubuntu 16.04 (and also with 4.5.11
on Centos 7.4) when using -I and -n together.

This is the version of xargs:
$ xargs --version
xargs (GNU findutils) 4.7.0-git
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Eric B. Decker, James Youngman, and Kevin Dalley.

I try

$ echo a b c d e f | xargs -I_ -n1 echo _xxx
a b c d e fxxx

-> this is expected, as the manpage states "unquoted blanks do not terminate
input items" for -I

But increasing -n leads to this surprising result:

$ echo a b c d e f | xargs -I_ -n2 echo _xxx
_xxx a b
_xxx c d
_xxx e f

 From my understanding -n2 means use 2 input items at max, and xargs is only
getting one here (because of -I ignoring the spaces). So the result should be
identical to the -n1 case. Also -I does not seem to have an effect here,
nothing is replaced.

Playing around shows even more unexpected stuff:

$ echo a b c d e f | xargs -n2 -I_ echo _xxx
a b c d e fxxx

Obviously the position of -n does matter here, but I cannot find the manpage
mentioning that.

Now, adding spaces as delimiters it gets even weirder:

$ echo a b c d e f | xargs -n1 -d" " -I_ echo _xxx
axxx
bxxx
cxxx
dxxx
exxx
f
xxx

That one looks good at first sight, but the manpage refers to -d as a single
character, so it does not include \n anymore. But the line break that echo
appends is treated as a delimiter, too.

Now, increasing -n again does not change the output. But it should:

$ echo a b c d e f | xargs -n2 -d" " -I_ echo _xxx
axxx
bxxx
cxxx
dxxx
exxx
f
xxx

So it looks to me that handling -I and -n in the same command line is broken
somehow.





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