On 10/14/12 7:26 AM, Dan Douglas wrote: > On Sunday, October 14, 2012 11:46:17 AM Wladimir Sidorenko wrote: >> To my mind '!' looks pretty much like a unary operator and '|' like a binary > one. > > This isn't as confusing as the associativity and nesting problem.
Think of `!' and `time' as reserved words that modify a pipeline rather than operators that begin one. You can stack `!' and `time' so that consecutive instances modify the same pipeline rather than delimit them. It's a little easier to see how ! ! is a no-op that way. There was an extensive discussion of this on the Posix list back a couple of years. Geoff Clare wrote the final version of a set of proposed changes that made a distinction between pipelines, `unadorned' pipelines, `negated' pipelines, `timed' pipelines, and allowed the `!' and `time' reserved words to modify the same pipeline. I'm not sure why a lot of that work didn't make it into the published standard, but it was clarifying. https://www5.opengroup.org/sophocles2/show_mail.tpl?CALLER=show_archive.tpl&source=L&listname=austin-group-l&id=12082 Chet -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
