Great to see quality post from real expert once in a while. Thanks! Xah ∑ http://xahlee.org/
☄ On Nov 29, 9:03 am, Stephane CHAZELAS <[EMAIL PROTECTED]> wrote: > There's a common confusion in this in the nature of /bin/sh. > There's no standard (neither POSIX nor Unix) that specifies that > /bin/sh should be any variant of the Bourne shell. Over the > years and on the different flavours of Unix, /bin/sh has been a > Thomson shell, Mashey shell, Bourne shell and all its variants, > Almquist shell, bash, ksh, zsh... > > For a very long time, on a wide range of Unices, it has been the > Bourne shell (modified slightly in different ways by the > different Unix vendors), so that's probably why it is still > nowadays confused with the Bourne shell even though it is still > so only on very few Unices (mainly only Solaris, Tru64 and some > SCO OSes). > > Nowadays, what the POSIX and Unix standards say is that a conformant Unix > should have somewhere (and the location is not specified but on > most Unices except those quoted above is generally /bin) a > command called "sh" that is an interpreter of the POSIX shell > language it defines. > > Shells that do implement an interpreter for that language > (though most shells of course have extensions which the > specification doesn't prohibit, such as many C compilers (like > gcc) have extensions to the standard C language as published by > the ISO) include (with lesser or greater accuracy) bash (2 or > above), the AT&T Korn shell (88<x> or 93<x> versions) and its > variants, the public domain Korn shell and its derivatives such > as posh, mksh or OpenBSD sh, modern variants of the Almquist > shell such as the NetBSD sh or dash. > > That shell language is based on a subset of the ksh88 language > and the Bourne shell is not a conformant implementation. Amongst > the feature of the POSIX/Unix sh that are not in the Bourne > shell are the $(...) form of command substitution, arithmetic > expansions as in $((...)), the processing of IFS that differs, > redirections of compound commands that no longer invoke a > subshell... That language is mostly backward compatible with the > Bourne syntax though there are a few small differences. > > To sum up, /bin/sh is no longer the Bourne shell. It is only so > on very old systems and on systems that have chosen to keep the > Bourne shell as /bin/sh for backward compatibility (and for > those, the standard sh is in another place such as > /usr/xpg4/bin on Solaris). Free software Unices have never had > the Bourne shell as their /bin/sh as the source code of the > Bourne shell has not been released until recently (except for > some early versions of BSD and they were then breaching the > law). > > -- > Stéphane -- http://mail.python.org/mailman/listinfo/python-list
