On Sun, Jan 12, 2003 at 09:22:55PM -0800, Randall R Schulz wrote: > Jon, > > Well, Cygwin does not include Bourne shell, it has BASH, ash and zsh, but > it does appear that the status returned by a parenthesized pipeline under > BASH is that of the last command in that pipeline.
As specified on the bash man page. > Strictly speaking, that's not at odds with the first part of what I said, > which is that the parent - child process relationship between processes in > a pipeline is not specified. > > So this leaves one puzzle: Why is it that Rolf is getting different results > for this command between Linux and Cygwin? > > (false | true) && echo true || echo false > > Rolf, which shells are you using on Linux and Cygwin? And what results? > At 20:53 2003-01-12, Jon LaBadie wrote: > >On Sun, Jan 12, 2003 at 02:21:45PM -0800, Randall R Schulz wrote: > >> Rolf, > >> > >> One posting is enough, really. > >> > >> There is no guaranteed or specified parent child relationship between the > >> processes in a pipeline. This means that you cannot predict which > >process's > >> status will be the one returned as that of the pipeline as a whole. > > > > > >> At 14:09 2003-01-12, Rolf Campbell wrote: > >> >/home/rcampbell> (true | true) && echo true || echo false > >> >true > >> >/home/rcampbell> (true | false) && echo true || echo false > >> >false > >> >/home/rcampbell> (false | true) && echo true || echo false > >> >true > >> >/home/rcampbell> (false | false) && echo true || echo false > >> >false > >> > > >> >The third test above yields different results when run on Linux. I'm > >> >wondering if this was the desired result or not? > > > > > >There is (or had been last I looked at the source) a defined relationship > >in the Bourne and Korn shells at least. > > > >The parent forks the last command in a pipeline which then becomes the > >parent of the other commands in the pipeline. Thus the original parent > >only sees the last command's exit status. > > > >This scheme was done to implement the following behavior back around > >System V.2 in the great Bourne shell "rewrite in C". > > > >>From the current Solaris man page for Bourne Shell: > > > > ... . Each command is run as a separate process; the > > shell waits for the last command to terminate. The exit > > status of a pipeline is the exit status of the last command > > in the pipeline. > > > >The addition of the pipefail option to recent ksh93 versions suggests > >this relation-ship scheme has been altered in those shells. But I > >do not think it appropriate to generically say there is no defined > >relationship as if it applies to every shell out there. > > > >-- > >Jon H. LaBadie [EMAIL PROTECTED] > > > -- > Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple > Bug reporting: http://cygwin.com/bugs.html > Documentation: http://cygwin.com/docs.html > FAQ: http://cygwin.com/faq/ > > >>> End of included message <<< -- Jon H. LaBadie [EMAIL PROTECTED] JG Computing 4455 Province Line Road (609) 252-0159 Princeton, NJ 08540-4322 (609) 683-7220 (fax) -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Bug reporting: http://cygwin.com/bugs.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
