07-25-2011
Purpose of - (hypen) in script or command line
Hi,
I am new for unix and I am following ABS guide. What is the purpose of - (hypen ) in the below command and What it will do in this?. Can anyone explain it in detail. Rest of the things in the below command I understood somewhat.
(cd /source/directory && tar cf - . ) | (cd /dest/directory && tar xpvf -)
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chroot(1M) System Administration Commands chroot(1M)
NAME
chroot - change root directory for a command
SYNOPSIS
/usr/sbin/chroot newroot command
DESCRIPTION
The chroot utility causes command to be executed relative to newroot. The meaning of any initial slashes (/) in the path names is changed
to newroot for command and any of its child processes. Upon execution, the initial working directory is newroot.
Notice that redirecting the output of command to a file,
chroot newroot command >x
will create the file x relative to the original root of command, not the new one.
The new root path name is always relative to the current root. Even if a chroot is currently in effect, the newroot argument is relative to
the current root of the running process.
This command can be run only by the super-user.
RETURN VALUES
The exit status of chroot is the return value of command.
EXAMPLES
Example 1: Using the chroot Utility
The chroot utility provides an easy way to extract tar files (see tar(1)) written with absolute filenames to a different location. It is
necessary to copy the shared libraries used by tar (see ldd(1)) to the newroot filesystem.
example# mkdir /tmp/lib; cd /lib
example# cp ld.so.1 libc.so.1 libcmd.so.1 libdl.so.1 libsec.so.1 /tmp/lib
example# cp /usr/bin/tar /tmp
example# dd if=/dev/rmt/0 | chroot /tmp tar xvf -
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO
cd(1), tar(1), chroot(2), ttyname(3C), attributes(5)
NOTES
Exercise extreme caution when referencing device files in the new root file system.
References by routines such as ttyname(3C) to stdin, stdout, and stderr will find that the device associated with the file descriptor is
unknown after chroot is run.
SunOS 5.10 15 Dec 2003 chroot(1M)