Re: [libvirt] [PATCH] [TCK] Convert scripts to also run with dash

On 11/15/2010 12:08 PM, Stefan Berger wrote: As a shell argument in isolation, "\1" is undefined in POSIX, but "\\1" and '\1' are both the two-character strings for \ and 1. Then, add printf or echo into the mix. echo is required to do further interpolation of some \ sequences (although not all shells enforce this by default), but not all sequences. For echo, dash does some non-required interpolations that bash in xpg_echo mode does not do; but for printf, both bash and dash provide non-required interpolations. Printf is only required to do \ interpolation of its first argument, and of any subsequent arguments that line up with %b in the first argument (and what's worse, the interpolations required of the two positions of printf arguments are different). Therefore: echo '\1' => undefined by POSIX (bash with xpg_echo outputs \1, bash in normal mode outputs \1, dash outputs char(1)) echo '\\1' => defined by POSIX, but not portable (bash with xpg_echo outputs \1, bash in normal mode outputs \\1, dash outputs \1) echo "\1" => doubly undefined by POSIX echo "\\1" => same problem as echo '\1' echo '\01' => defined by POSIX, but not portable (bash with xpg_echo outputs char(1), bash in normal mode outputs \01, dash outputs char(1)) printf %s\\n '\1' => well-defined as \1 everywhere printf %s\\n "\1" => undefined by POSIX, although it tends to portably output \1 printf %s\\n "\\1" => well-defined as \1 everywhere printf '\1' => well-defined as char(1) everywhere printf %b '\1' => undefined by POSIX, although it tends to portably output char(1) printf %b '\01' => well-defined as char(1) everywhere printf %b "\1" => undefined by POSIX, although it tends to portably output char(1) -- Eric Blake eblake(a)redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org