Very Computer

by **kevi** » Mon, 21 Jan 2002 16:42:36

Hi,

When I read someone else's shell script, I find the following sentence,
Would someone tell me what does it mean?

: ${VOLROOT_DIR:=$__VXVM_ROOT_DIR}

Thanks

Kevin

by **Tony Lawrenc** » Mon, 21 Jan 2002 17:22:48

> Hi,

> When I read someone else's shell script, I find the following sentence,
> Would someone tell me what does it mean?

> : ${VOLROOT_DIR:=$__VXVM_ROOT_DIR}

It means that VOLROOT_DIR will be set to $_VXM_ROOT_DIR if VOLROOT_DIR
isn't already set. But if it already has been set, it won't change.
Oftyen used to set fdefault values that can be overridden at the command
lne.

You'll find this and other useful shortcuts like this in the man page for your shell.

--
Tony Lawrence
SCO/Linux Support Tips, How-To's, Tests and more: http://pcunix.com

by **Chris F.A. Johnso** » Tue, 22 Jan 2002 03:02:46

> > When I read someone else's shell script, I find the following sentence,
> > Would someone tell me what does it mean?

> > : ${VOLROOT_DIR:=$__VXVM_ROOT_DIR}

> It means that VOLROOT_DIR will be set to $_VXM_ROOT_DIR if VOLROOT_DIR
> isn't already set. But if it already has been set, it won't change.

Actually, it sets VOLROOT_DIR if it is unset or its length is zero.

To set VOLROOT_DIR only if it is unset:

: ${VOLROOT_DIR=$__VXVM_ROOT_DIR}

Quote:> Oftyen used to set fdefault values that can be overridden at the command
> lne.

> You'll find this and other useful shortcuts like this in the man page for your shell.

--
Chris F.A. Johnson http://cfaj.freeshell.org
===================================================================
My code (if any) in this post is copyright 2002, Chris F.A. Johnson
and may be copied under the terms of the GNU General Public License

Very Computer

What does it mean: ${VOLROOT_DIR:=$__VXVM_ROOT_DIR}

What does it mean: ${VOLROOT_DIR:=$__VXVM_ROOT_DIR}

What does it mean: ${VOLROOT_DIR:=$__VXVM_ROOT_DIR}

What does it mean: ${VOLROOT_DIR:=$__VXVM_ROOT_DIR}