From mboxrd@z Thu Jan 1 00:00:00 1970 From: dot@dotat.at (Tony Finch) Date: Fri, 15 Jul 2016 10:00:54 +0100 Subject: [TUHS] Shell control through external commands In-Reply-To: References: <4fcf31ef-50af-10b5-0c34-ad647ed10a4e@aueb.gr> Message-ID: Dave Horsfall wrote: > On Thu, 14 Jul 2016, Clem Cole wrote: > > > Could you be confusing the fact the true and false were implemented by > > external commands in some early shell's > > And on the Mac and FreeBSD, they still are (as well as being builtins). > At one time they were shell scripts e.g. "exit 0" for "true". This isn't a BSDism: POSIX requires that most built-in commands also exist as executables on the PATH. The exceptions are the "special built-in commands" which manipulate the shell command language state, e.g. break and set. http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_14 Tony. -- f.anthony.n.finch http://dotat.at/ - I xn--zr8h punycode Humber, Thames, Dover: West or southwest 4 or 5, increasing 6 at times. Slight or moderate. Mainly fair. Good.