Re: [libvirt] GNU awk vs BSD awk?

On 12/01/2010 09:08 PM, Justin Clift wrote: GNU awk, or GNU make? There's a difference :) With regards to make, libvirt is firmly in the camp of GNU make and nothing else. We use too many extensions specific to gmake that just aren't present in other implementations, and it is too difficult to figure out how to rewrite those in the lowest-common-denominator of POSIX make syntax. (Side note - the Austin Group, which is in charge of updating the POSIX standard, is currently reviewing several proposals to increase the lowest-common-denominator, such as by standardizing something similar to gmake's $(shell) or BSD makes != assignment, but that is a lengthy process, and you can't expect it to make a difference overnight). With regards to awk, libvirt should be able to get by with any POSIX-compliant awk; if you find a counter-example where things are broken while using BSD awk, it should be relatively easy to patch things to get it working again. Note, however, that there are multiple awk flavors out there; oawk (called awk on some systems) is NOT posix-compliant, and is inadequate for libvirt's needs; while mawk, nawk, BSD awk, and gawk should all be interchangeable given a script that sticks only to POSIX features. In fact, autoconf requires a decent awk just for running ./configure, and substitutes $AWK appropriately. I see several uses where libvirt is hard-coded to awk (for example, tools/virt-pki-validate), but most of those are portable even to oawk, because they avoid POSIX features that were not present in older awk; but I have not audited all of libvirt's awk usages. http://www.gnu.org/software/autoconf/manual/autoconf.html#index-g_t_0040c... gives a good overview of features to look for when auditing awk scripts for POSIX vs. oawk compliance, as well as some common bugs in almost-POSIX-compliant implementations and how to work around those bugs. -- Eric Blake eblake(a)redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org