Re: How do I invoke a shell command during the parsing phase?

From: msheppard_climax (msheppard_at_[hidden])
Date: 2003-09-26 10:11:08

--- In jamboost_at_[hidden], Vladimir Prus <ghost_at_c...> wrote:
> msheppard_climax wrote:
> 
> > I want to invoke a shell command during the parsing phase which 
will
> > update a source target with information from the Jamfile, but I 
can't
> > see how to do it. I'm looking for the Jam equivalent of doing:
> >
> > $(shell whatever 2>&1 >/dev/null)
> >
> > in GNU Make. Is there a way to do that in Boost Jam?
> 
> Nope, there's no such facility. It was talked about, but nothing 
happened, 
> probably because it's not that simple. 

I couldn't find that discussion with a search of the jamboost Yahoo 
group, do have a link to it? I had imagined it wouldn't be that hard 
a feature to add, but obviously it is.

> Why do you need it? Maybe the problem can be solved in some other 
way?

I want it to run a program which will write out a C++ file which just 
#includes a number of other C++ files. The list of files to #include 
originates from the jamfile and would be passed in on the command 
line. If the generated file exists and already includes exactly the 
same list of files it's left alone, if not it's updated. The 
generated file is then compiled rather than all the individual files 
it includes.

This needs to be done prior to dependency checking so that the 
timestamp on the generated file can be checked. If you avoid 
checking the timestamp on this file and instead use explicit calls to 
DEPENDS/INCLUDES to make the object file depend on the files the 
generated file includes then jam would fail to notice if the list of 
files had changed since the previous invocation. If none of the 
included files had been changed jam then wouldn't do the compilation 
when it should.

I guess a work-around would be to run the program as part of the 
normal action commands and have it exit non-zero if it updated the 
file causing jam to bail out. The user would then have to re-run jam 
to get it to compile the updated file. A bit inelegant, but it 
should work.

Mark.