[jamming] BJam's command/shell execution

[Diane Holt]

Boost Jam has this (it's what I patterned the Command built-in after):

The SHELL Rule

rule SHELL ( command )

SHELL executes *command*, and then returns the standard output of *command*.
SHELL only works on platforms with a popen() function in the C library. On
platforms without a working popen() function, SHELL is implemented as a
no-op. SHELL works on Unix, MacOS X, and most Windows compilers. SHELL is a
no-op on Metrowerks compilers under Windows.


On 3/22/07, Joshua ChaitinPollak <jpollak at kivasystems.com> wrote:
>
> Hi,
>
> I'm using BJam, and I can't figure out how to get the shell script
> execution working. I know there was a recent thread about a COMMAND
> patch for Jam, and I'm looking forward to that, but for now I'm using
> BJam and I don't have the time to apply patches and compile, etc.
>
> I've ported most of my project to Jam, but I have one Makefile I
> can't figure out how to ditch. I have this Makefile code:
>
> REVISION := $(shell svnversion)
> OLD_REVISION := $(shell cat revision.cpp 2> /dev/null)
>
> revision.cpp:
> ifeq (,$(findstring \"{REVISION}\", ${OLD_REVISION}))
>    @echo "void config::getRevision(std::string& rev) { rev = \"$
> {REVISION}\"; } >> revision.cpp
> endif
>
> This (should) effectively (re)builds revision.cpp if the revision has
> changed. My program depends in revision.cpp, so if revision has
> changed, the file gets rebuild and the program gets rebuilt.
>
> How would I do this in a Jam way? I guess I could call a shell script
> to build the revision.cpp file all the time, but I'd rather not
> unless its out of date.
>
> -Josh
>
> --
> Joshua ChaitinPollak
> Software Engineer
> Kiva Systems
>
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