Date: Mon, 14 Jan 2002 23:10:29 +0200 From: Giorgos Keramidas <keramida@freebsd.org> To: adrian kok <adriankok2000@yahoo.com.hk> Cc: questions@freebsd.org Subject: Re: /dev/null 2>&1 Message-ID: <20020114211029.GD31045@hades.hell.gr> In-Reply-To: <20020114173304.68462.qmail@web21210.mail.yahoo.com> References: <20020114173304.68462.qmail@web21210.mail.yahoo.com>
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On 2002-01-15 01:33:04, adrian kok wrote:
> Dear all
>=20
> What is the meaning of /dev/null 2>&1
>=20
> Thank you
You'll see constructs like this in scripts that read:
command >/dev/null 2>&1
That is a Bourne shell idiom (does not work in CSH and friends), that
means ``redirect standard output to /dev/null'' and then ``redirect
file-descriptor 2 (stderr) to the same place as 1 (stdout)''.
The purpose of all this is to stop `command' from producing *any* kind
of output, on standard output and error.
Another use could be to save all output from a command in a file, both
standard output and standard error. I customarily build my kernels
and update my FreeBSD systems with commands like this:
# cd /usr/src
# make buildworld >buildworld.log 2>&1 &
# logout
Then after buildworld finishes ...
# cd /usr/src
# make buildkernel >buildkernel.log 2>&1 &
# logout
This way, all output from `make buildworld' is saved in the file
/usr/src/buildworld.log and all output from `make buildkernel' is
saved in /usr/src/buildkernel.log. A few hours later, I can browse
the file for interesting messages.
Cheers,
--=20
Giorgos Keramidas . . . . . . . . . keramida@{ceid.upatras.gr,freebsd.org}
FreeBSD Documentation Project . . . http://www.freebsd.org/docproj/
FreeBSD: The power to serve . . . . http://www.freebsd.org/
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