topic Re: variable in if in Operating System - Linux

variable in if

Gemini_2 — Mon, 14 Apr 2008 21:50:07 GMT

I would like to change the following two statements into one.

"list=$(ls -1 $xturns/tur*)
if [ "$list" ];then"

how can I do that?

i tried
if [ $list=$(ls -1 $xturns/tur*) ]; then

but...it doesnt work...

for shell script..please advise

Re: variable in if

James R. Ferguson — Mon, 14 Apr 2008 22:42:08 GMT

Hi Gemini:

# LIST=$(ls -1 /tmp/tur* 2>/dev/null||echo "empty")

# echo ${LIST}

...would return a list of files or the word "empty"

Is that your objective?

Regards!

...JRF...

Re: variable in if

Gemini_2 — Mon, 14 Apr 2008 22:44:08 GMT

not quite.

I just want to condense two statements into one in the if statement. can that be done?

Re: variable in if

James R. Ferguson — Mon, 14 Apr 2008 22:57:58 GMT

Hi:

Again, I'm not sure of your objective, but:

if [ -z "$(ls -1 /tmp/gemini* 2>/dev/null)" ]; then
echo "empty"
else
echo "ok"
fi

...Note that no variable is necessary for capturing the list.

Regards!

...JRF...

Re: variable in if

Gemini_2 — Mon, 14 Apr 2008 23:01:13 GMT

ah, you are right.. I didnt make myself clear. I left one important part. my bad.

use your example

if [ -z "$(ls -1 /tmp/gemini* 2>/dev/null)" ]; then
echo "empty"
else
echo "ok"
fi

what if i want to echo the result of ls -l? then what do you do

thanks for your patience

Re: variable in if

James R. Ferguson — Mon, 14 Apr 2008 23:12:12 GMT

Hi (again):

I think the best we might do is:

# LIST=$(ls -1 /tmp/gemini* 2>/dev/null)
# [ -z "${LIST}" ] && echo "empty" || echo ${LIST}

...yes, that's two statements, but ...

Regards!

...JRF...

Re: variable in if

Gemini_2 — Mon, 14 Apr 2008 23:22:30 GMT

I was hoping to have something like this

[ -z "${LIST}=$(ls -1 /tmp/gemini* 2>/dev/null)" ] && echo "empty" || echo ${LIST}

but, i know my syntax is not quite right...

anyway..thaks for your help..

Re: variable in if

Steven Schweda — Tue, 15 Apr 2008 00:28:48 GMT

Just so I understand, ...

You have two simple statements which work
properly, and are easy to understand, and you
wish to combine them into a single, more
complex statement because you think that that
will look better somehow?

Is that the goal here?

Re: variable in if

Gemini_2 — Tue, 15 Apr 2008 00:34:30 GMT

I know

I just thought that option is available...but I forgot it...I just want to know it for memory refresh purple

but, thanks for your help anyway

Re: variable in if

Dennis Handly — Sat, 17 Sep 2011 02:01:28 GMT

>I would like to change the following two statements into one.

You would do the obvious:
if [ "$(ls -1 $xturns/tur*)" ]; then

Compare to JRF's solution where -z tests for empty string.

>what if I want to echo the result of ls -l?

As Steven said, why make it harder to understand?

But if you insist, if may be something like:
[ -z "${LIST:=$(ls -1 /tmp/gemini* 2>/dev/null)}" ] && echo "empty" || echo ${LIST}

Note: You would really need to unset LIST to make sure it gets set.

Re: variable in if

Gemini_2 — Tue, 15 Apr 2008 20:59:14 GMT

yes, yes, your answer is correct.

it was very closed to what I had, but I placed my quote place wrong.

thanks for your help!

ps: you also dont need the ":=", you only need "="

Re: variable in if

James R. Ferguson — Tue, 15 Apr 2008 21:59:13 GMT

Hi (again) Gemini:

I too had concocted a solution identical to by Dennis'. It would seem to be correct (using '=' instead of the ALGOL assignment ':=' operator) and yet failed/fails for me:

# [ -z "${LIST=$(ls -1 /tmp/gemini* 2>/dev/null})" ] && echo "empty" || echo ${LIST}

This does not yield any results for me; rather it gives and empty list. Comments, gentlemen?

Regards!

...JRF...

Re: variable in if

Gemini_2 — Tue, 15 Apr 2008 22:20:34 GMT

oh, he had a little typo in his statement..
I corrected in my script, but I didnt point it out.

this should be right.

[ -z "${LIST=$(ls -1 /tmp/gemini* 2>/dev/null)}" ] && echo "empty" || echo ${LIST}

Re: variable in if

Dennis Handly — Sat, 17 Sep 2011 02:03:42 GMT

I made a typo, swap the "}" and ")":
[ -z "${LIST:=$(ls -1 /tmp/gemini* 2>/dev/null)}" ]

>you also don't need the ":=", you only need "="

Yes, only because $LIST must NOT be set at all.

>JRF: This does not yield any results for me; rather it gives and empty list. Comments, gentlemen?

Did you do this as root? You have created a file in /dev: null}

Re: variable in if

James R. Ferguson — Tue, 15 Apr 2008 22:42:50 GMT

Hi Gemini & Dennis:

Aahhaa! Yes, OK.

> Dennis: I made a typo, swap the "}" and ")":

Oh, OK, I kept missing that :-{

> Dennis: Did you do this as root? You have created a file in /dev: null}

And, again, yes! I did and I had a file in '/dev/' so named.

Very nice solution, Dennis.

Regards!

...JRF...