On Tue, Mar 19, 2002 at 10:46:04AM +1100, [EMAIL PROTECTED] wrote:
>
> In an attempt to stimulate non-golf threads:
>
> .. Has anybody done any really interesting Perl "hacks" that they are
> proud of?
Yeah, I do actually. Recently I was writing a program that needed
to (shell) source a file, to get some environment variables set,
and use those variables in further calculations.
I could of course have written a shell wrapper that sourced the file,
then started my program. But I decided I just wanted a single program.
To source a shell file, one cannot use 'system' - that would start
a child process, and setting the environment in the child is pointless.
So, I decided to use a trick, a double exec. First I exec a shell
that is sourcing the file with the environment variables, then I
exec the original program - with a special argument to indicate the
variables have been set.
The relevant part of said program follows.
Abigail
my $ENVIRONMENT = "/some/file/somewhere";
if (@ARGV && $ARGV [0] eq '--sourced_environment') {
shift;
}
else {
if (-f $ENVIRONMENT) {
#
# Now we perform a double exec. The first exec gives us a shell,
# allowing us the source the file with the environment variables.
# Then, from within the shell we re-exec ourself - but with an
# argument that will prevent us from going into infinite recursion.
#
# We cannot do a 'system "source $ENVIRONMENT"', because
# environment variables are not propagated to the parent.
#
# Note the required trickery to do the appropriate shell quoting
# when passing @ARGV back to ourselves.
#
@ARGV = map {s/'/'"'"'/g; "'$_'"} @ARGV;
exec << " --";
source '$ENVIRONMENT'
exec $0 --sourced_environment @ARGV;
--
die "This should never happen.";
}
}
