On 03/21/2017 12:08 PM, Greg Wooledge wrote: > The code that makes bash behave differently when "jobs" is one of the > commands in a pipeline/subshell is kind of a hack. It's probably not > extremely well known outside of this mailing list, but I suspect many > people have used it without realizing what it is. It's a fairly intuitive > hack.
And it's for more than just 'jobs' - at least 'trap' relies on it, too. > > I've got no strong opinions about whether the "jobs hack" should be > documented. POSIX documents the 'jobs'/'trap' hack thus: When a subshell is entered, traps that are not being ignored shall be set to the default actions, except in the case of a command substitution containing only a single trap command, when the traps need not be altered. Implementations may check for this case using only lexical analysis; for example, if `trap` and $( trap -- ) do not alter the traps in the subshell, cases such as assigning var=trap and then using $($var) may still alter them. For more background on this, see: http://austingroupbugs.net/view.php?id=53 although that bug specifically mentions 'trap', and concludes that a separate bug may need to be opened (which I could not find) giving the same treatment to 'jobs'. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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