Hello,

The function "pcomplete/xargs" (in lisp/pcmpl-unix.el) was set up to
treat xargs with the usage pattern

       xargs [command [initial-arguments]]

Whereas the usage of xargs is actually

       xargs [options] [command [initial-arguments]]

So options to xargs itself were not being completed (assuming
pcomplete-default-completion-function is capable of generating these
completions.)

I added this, treating any string that begins with a "-" following xargs
as an xargs argument and the first string that doesn't as the command
being run by xargs. For example,

       xargs -I{} -0 rm -r
       
-I and -0 will be completed as arguments to xargs (using
 pcomplete-default-completion-function) and rm as a command (using pcomplete-command-completion-function).
 
Commit log entry:

* lisp/pcmpl-unix.el (pcomplete/xargs): Add support for completing xargs
options, including the ability to distinguish them from the command
xargs runs.

Karthik Chikmagalur