03-25-2002
redirecting/piping
i want to fully undertand redirecting/piping. i know most of the basic stuff, like ls|less or cat file|grep hello etc etc. but there are a somethings like find / -name file 2>/dev/null. what's is the 2? i know it redirects the errors (at least Permission denied ones) to /dev/null (the unix blackhole).
can someone tell what the 2 is for, up there? and... any site i can check out to understand complex piping?
thx in advance
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RSH(1) BSD General Commands Manual RSH(1)
NAME
rsh -- remote shell
SYNOPSIS
rsh [-46dn] [-l username] [-p port] host [command]
rsh [-46dn] [-p port] username@host [command]
DESCRIPTION
rsh executes command on host.
rsh copies its standard input to the remote command, the standard output of the remote command to its standard output, and the standard error
of the remote command to its standard error. Interrupt, quit and terminate signals are propagated to the remote command; rsh normally termi-
nates when the remote command does. The options are as follows:
-4 Use IPv4 addresses only.
-6 Use IPv6 addresses only.
-d The -d option turns on socket debugging (using setsockopt(2)) on the TCP sockets used for communication with the remote host.
-l username By default, the remote username is the same as the local username. The -l option or the username@host format allow the remote
name to be specified.
-n The -n option redirects input from the special device /dev/null (see the BUGS section of this manual page).
-p port Uses the given port instead of the one assigned to the service ``shell''. May be given either as symbolic name or as number.
If no command is given, note that rlogin(1) is started, which may need a different daemon (rlogind(8) instead of rshd(8)) run-
ning on the server; you want to pass the rshd(8) port number in that case.
If no command is specified, you will be logged in on the remote host using rlogin(1).
Shell metacharacters which are not quoted are interpreted on local machine, while quoted metacharacters are interpreted on the remote
machine. For example, the command
rsh otherhost cat remotefile >> localfile
appends the remote file remotefile to the local file localfile, while
rsh otherhost cat remotefile ">>" other_remotefile
appends remotefile to other_remotefile.
FILES
/etc/hosts
SEE ALSO
rcmd(1), rlogin(1), rcmd(3), hosts.equiv(5), rhosts(5), environ(7)
HISTORY
The rsh command appeared in 4.2BSD.
BUGS
If you are using csh(1) and put a rsh in the background without redirecting its input away from the terminal, it will block even if no reads
are posted by the remote command. If no input is desired you should redirect the input of rsh to /dev/null using the -n option.
You cannot run an interactive command (like rogue(6) or vi(1)) using rsh; use rlogin(1) instead.
Stop signals stop the local rsh process only; this is arguably wrong, but currently hard to fix for reasons too complicated to explain here.
BSD
March 9, 2005 BSD