stderr redirection on FreeBSD
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From: Eze on 20 Dec 2008 09:45 Greetings! I'm trying for the first time FreeBSD (as a virtual machine). I invoked /bin/sh but found that stderr redirection does not seem to happen: $ givemeanerror >/dev/null 2>&1 prints nothing in Linux, but I get givemeanerror: not found in FreeBSD. Does anybody know why? (Ditto if I try givemeanerror 2>&1 >/dev/null.)
From: Andre Majorel on 20 Dec 2008 11:19 On 2008-12-20, Eze <garzon.lucero(a)gmail.com> wrote: > Greetings! I'm trying for the first time FreeBSD (as a virtual > machine). I invoked /bin/sh but found that stderr redirection > does not seem to happen: > > $ givemeanerror >/dev/null 2>&1 > > prints nothing in Linux, but I get > > givemeanerror: not found > > in FreeBSD. Does anybody know why? (Ditto if I try givemeanerror 2>&1 > >/dev/null.) What is your shell on the FreeBSD host ? -- Andr� Majorel <URL:http://www.teaser.fr/~amajorel/> "After 15 minutes, I wanted to marry her. After a half hour, I completely gave up the idea of snatching her purse." -- _Take the Money and Run_
From: Eze on 20 Dec 2008 14:36 The default shell is tcsh, but I deliberately invoked sh, which is linked to /bin/sh. I assume this is some variant of the Bourne shell, isn't it? (The man pages are not available.) On Dec 20, 5:19 pm, Andre Majorel <che...(a)halliburton.com> wrote: > On 2008-12-20, Eze <garzon.luc...(a)gmail.com> wrote: > > > Greetings! I'm trying for the first time FreeBSD (as a virtual > > machine). I invoked /bin/sh but found that stderr redirection > > does not seem to happen: > > > $ givemeanerror >/dev/null 2>&1 > > > prints nothing in Linux, but I get > > > givemeanerror: not found > > > in FreeBSD. Does anybody know why? (Ditto if I try givemeanerror 2>&1 > > >/dev/null.) > > What is your shell on the FreeBSD host ? > > -- > André Majorel <URL:http://www.teaser.fr/~amajorel/> > "After 15 minutes, I wanted to marry her. After a half hour, I completely > gave up the idea of snatching her purse." -- _Take the Money and Run_
From: Sven Mascheck on 20 Dec 2008 18:07 Eze wrote: > $ givemeanerror >/dev/null 2>&1 > > prints nothing in Linux, but I get > > givemeanerror: not found > > in FreeBSD. This redirection is a corner case; usually a redirection is only referred to the command. But here, most shells redirect their own output - in case the command could not be found. (the point might be if the forked child has its output already redirected when it searches the command) Grouping is a way to influence it; you will see this: $ givemeanerror 2>/dev/null givemeanerror: not found $ { givemeanerror; } 2>/dev/null $ I know two shells which need this grouping: the traditional Bourne shells and the Almquist shell variants (FreeBSD /bin/sh is such a variant). As exception, this was changed in dash with release 0.4.7 (dec/02). If dash had not changed it, it were one of the few properties to identify an Almquist shell without just eliminating other possibilities. (Another one is "cmd > file*", which is not expanded, and which is handled likewise by the traditional Bourne shell, too). The time command is another interesting corner case. It is not a built-in, but usually even part of the grammar; thus you also need grouping to redirect its output. Seems difficult to get all this right under all possible conditions. I just stumbled over the unset error message in parameter substitution: { : ${unsetvar?error}; } 2>/dev/null bash is confused about where stderr should point to. The shell doesn't hang, just stderr is lost (and thus the prompt); hit ctrl-c to fix. It seems to have been fixed with one of the recent patches, though. Especially shells have a hard job to behave orthogonally.
From: André Gillibert on 20 Dec 2008 18:35
Eze <garzon.lucero(a)gmail.com> wrote: > The default shell is tcsh, but I deliberately invoked sh, which is > linked to /bin/sh. I assume this is some variant of the Bourne shell, > isn't it? (The man pages are not available.) > Google and wikipedia helped. It might be a derived from ash. <http://www.in-ulm.de/~mascheck/various/ash/#freebsd> <http://en.wikipedia.org/wiki/Almquist_shell> contains: > Derivatives of ash are installed as the default shell (/bin/sh) on FreeBSD, NetBSD, DragonFly BSD and Minix. Originally, it was a clone of Bourne shell. However, you should check that it isn't a simple symbolic link to tcsh. I installed tcsh and dash (Debian's fork of ash) on my Gentoo system. tcsh exposes the behavior you've seen, but dash doesn't. |