topic Re: difference between $LOGDIR and ${LOGDIR} ? in Operating System - HP-UX

difference between $LOGDIR and ${LOGDIR} ?

Sammy_2 — Fri, 18 Nov 2005 14:55:39 GMT

Is there a difference in parentheses being out as oppose to not having them at all.
we are trying to run a job via cron. (hpux 11.11)and have a mixture of these parentheses and want to make sure we get the same result in all cron entries.

Please explain.

Re: difference between $LOGDIR and ${LOGDIR} ?

Rodney Hills — Fri, 18 Nov 2005 15:14:27 GMT

Usually they are used when the variable is embedded with other text.

example-
echo ${LOGDIR}A $LOGDIRA

Will display variable LOGDIR followed with an A, while LOGDIRA the shell will think it is the variable name.

{} are also used for arrays and some other operations that are available on variables. See man ksh for more.

HTH

-- Rod Hills
and
${LOGDIR}A

Re: difference between $LOGDIR and ${LOGDIR} ?

Devender Khatana — Fri, 18 Nov 2005 15:26:32 GMT

Hi,

It is used for defining a new variable according to the value of previous variable. By defining it like this shell understand that this is a variable previously defined.

For ex.
server1:/home/hp/>>export LOGNAME=123
server1:/home/hp>>echo $LOGNAME
123
server1:/home/hp>>export LOGNAME1=${LOGNAME}newlogname
server1:/home/hp>>echo $LOGNAME1
123newlogname

(The value is new variable is appended to previous value of similar variable)

Some scripting experts will describe it better otherwise.

HTH,
Devender

Re: difference between $LOGDIR and ${LOGDIR} ?

A. Clay Stephenson — Fri, 18 Nov 2005 15:48:25 GMT

If you use the {}'s each and every time, you will never get into trouble (parsing-wise); the converse is not true. It's a very good habit to learn.

Re: difference between $LOGDIR and ${LOGDIR} ?

James R. Ferguson — Fri, 18 Nov 2005 15:50:49 GMT

Hi Sammy:

As noted, bounding your variable names with curly braces avoids ambiguitites in what you versus the shell interpret as the variable name.

Personally, I consider it simply good practice to always encapsulate variables within curly braces in shell programming.

Regards!

...JRF...

Re: difference between $LOGDIR and ${LOGDIR} ?

Jeff_Traigle — Fri, 18 Nov 2005 15:53:28 GMT

Also note you're asking about braces (i.e. {}), not parentheses (i.e. ()). Big difference in how the shell interprets these. It's best to say what you mean in cases where you aren't typing what you're really referencing.

${something} represents the value of the some variable.

$(something) represents executing whatever "something" is. This is also represented as `something` in older shells and is still used for backwards compatibility.

Re: difference between $LOGDIR and ${LOGDIR} ?

Sammy_2 — Fri, 18 Nov 2005 16:11:53 GMT

Point taken. thanks to Rod and Devender for providing examples which was reinforced by JRF and Clay. Jeff made another good pt about parentheses.

Thanks to all