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From Cris Perdue <>
Subject [io] Re: ProcessUtils and support classes offer
Date Wed, 01 Sep 2004 23:18:41 GMT
Hello Matthew,

Thanks for checking out the ProcessUtils documentation!  Unfortunately 
some of my commons-dev digest emails have been getting sorted into my 
Spam folder, so your reply only showed up as I went to fix up spam 
processing.  Hopefully I will get the rest of them.

Matthew Hawthorne wrote:
 > Cris Perdue wrote:
 > > The purpose of the main ProcessUtils class is to make it simpler to 
 > > external programs and receive the results back.  It was inspired
 > > especially by the TCL exec function and also resembles the Perl
 > > backtick operator.  A simple call to "df" using the simplest form
 > > of call could look something like:
 > >
 > > String filestats = ProcessUtils.exec(new String[] {"df"});
 > >
 > > The package handles program output to "standard error" and nonzero 
exit codes.
 > This may be a good fit for commons-io
 > (   A class like ProcessUtils
 > seems interesting, but it would definitely need some extensive testing
 > on different platforms to make sure it's OK.
 > Consider submitting your stuff as a Bugzilla enhancement, so that  the
 > commons-io developers can take a look when they get a chance.
 > I believe the javadocs state that ProcessUtils throws an exception if
 > anything is written to stderr.  I would like it if this were
 > customizable, since a lot of programs write warnings and such to
 > stderr, but still keep on running.  Perhaps it could become some type
 > of callback mechanism.

Yes, this is a good case to handle.  The "dual Writer" version of exec 
can handle this and exit status also, e.g.:

  StringWriter ow = new StringWriter();
  StringWriter ew = new StringWriter();
  int status = ProcessUtils.exec(new String[] {"rpm", "-ql", 
"somepackage"}, ow, ew);
  String output = ow.toString();

It would be simple to allow null values for the Writers and ignore the 
output.  That would avoid the need for the app to create one or both of 
the Writers.

A ProcessUtils.Exception is actually an object with all of the results 
of the program.  It has a string with all the contents of stdout, a 
string with stderr, and an integer exit status.  One could make a form 
that always returns an object like this and never throws, or one could 
pass the object to "exec", which would fill it in and never throw.  I 
rather like this option.  A simple call would look something like:

  ProcessUtils.Exception ex = new ProcessUtils.Exception();
  String output = ProcessUtils.exec(new String[] {"df"}, ex);
Perhaps a null value for the extra parameter could mean "ignore exit 
status and output to stderr".  (And by the way in this case I would 
rename the Exception and make it a top-level class.) So there are a 
couple of additional options I can see.

Thanks also for the suggestions on how to submit this.


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