for shell script how to store the output of another task other than this command self

vvpp · 11-11-2009, 10:01 PM

Hi guys,

In my shell script, I failed to store the result of an external command, which will exit instantly just after sending msg to another task that will print some info out, into a variable.
For example, let's assume the command name is "alarm_dbg", which just sends a "PRINT" msg to another task like "alarm" then returns, and the task "alarm" will print the info out, so my sentence in script would be like

Code:

val=`alarm_dbg` #external command
echo "val=$val"

but the return value is null, as

Code:

# here the executed result by alarm task is displayed
# but val variable is null
val=

Does anyone know how to store the info into this variable just using shell script other than modify the code to let "alarm_dbg" self to print out the info?

Thanks in advance.

ghostdog74 · 11-11-2009, 10:23 PM

if you are using bash, try using $() syntax instead of backticks

evo2 · 11-11-2009, 11:01 PM

If you run alarm_dbg on the command line, what happens?
It prints some text? Is this what you want to store in your variable, val?

Also you didn't tell us what shell you are using for the script. Are we correct assuming that it is bash?

Evo2.

vvpp · 11-11-2009, 11:23 PM

1> it just prints out the info as that of
2> yeah, it does print texts, and which are what I want.
3> sorry for no mention about shell name, it is bash, as you assumed.

Quote:

Originally Posted by evo2

If you run alarm_dbg on the command line, what happens?
It prints some text? Is this what you want to store in your variable, val?

Also you didn't tell us what shell you are using for the script. Are we correct assuming that it is bash?

Evo2.

vvpp · 11-11-2009, 11:26 PM

yeah, it's bash, but it seems $() take same effect as ``
and the "val" I got is still null

Quote:

Originally Posted by ghostdog74

if you are using bash, try using $() syntax instead of backticks

GrapefruiTgirl · 11-11-2009, 11:44 PM

A while back, I recall an "external" command or program of some sort, that for whatever reason was sending it's output through 'stderr' instead of 'stdout' as one would expect. Maybe this external command you are running is also doing the same?

At least to eliminate this as a possibility, try redirecting stderr into stdout when running the command whose output you wish for $val to trap.

Sasha

vvpp · 11-12-2009, 01:39 AM

Sasha，thanks for your idea, but this command is stdout too, in fact the output is done by another running task instead of this command, which just sends msg to the task to trigger the output.

Quote:

Originally Posted by GrapefruiTgirl

A while back, I recall an "external" command or program of some sort, that for whatever reason was sending it's output through 'stderr' instead of 'stdout' as one would expect. Maybe this external command you are running is also doing the same?

At least to eliminate this as a possibility, try redirecting stderr into stdout when running the command whose output you wish for $val to trap.

Sasha

evo2 · 11-12-2009, 02:29 AM

Um, the top posting has made this difficult to follow...

Quote:

Originally Posted by vvpp

1> it just prints out the info as that of

Yes but what?

Quote:

2> yeah, it does print texts, and which are what I want.

I'm just wondering if there are some escape sequences in there that could be giving you problems.

Did you try

Code:

val="`alarm_dbg`"

instead of just

Code:

val=`alarm_dbg`

?

Quote:

3> sorry for no mention about shell name, it is bash, as you assumed.

Ok.

Can you reproduce the problem with something other than "alarm_dbg"? Or perhaps let us know exactly what "alarm_dbg" is?

Evo2.

vvpp · 11-12-2009, 03:30 AM

Hi Evo2,

in fact the command "alarm_dbg" just sends msg to some running task to trigger the output. After the msg sent, "alarm_dbg" will return ok, so the val will be null for there is really no output for "alarm_dbg". I just want to collect the terminal output info printed by another running task, but failed.

Quote:

Originally Posted by evo2

Um, the top posting has made this difficult to follow...

Yes but what?

I'm just wondering if there are some escape sequences in there that could be giving you problems.

Did you try

Code:

val="`alarm_dbg`"

instead of just

Code:

val=`alarm_dbg`

?

Ok.

Can you reproduce the problem with something other than "alarm_dbg"? Or perhaps let us know exactly what "alarm_dbg" is?

Evo2.

evo2 · 11-12-2009, 04:18 AM

Please stop top posting. If you don't know what "top posting" means please refer to google.

You quoted my entire post below yours, but didn't answer any of the questions I asked. Why?

Quote:

Originally Posted by vvpp

in fact the command "alarm_dbg" just sends msg to some running task to trigger the output.
After the msg sent, "alarm_dbg" will return ok,

"return ok" Do you mean that it exits with a status of 0?

Quote:

so the val will be null for there is really no output for "alarm_dbg".

"null"? Does that mean an empty string or something else?

Quote:

I just want to collect the terminal output info printed by another running task, but failed.

This much I do understand, but I can't help you with the relevant information.

Evo2.

vvpp · 11-12-2009, 08:46 PM

Quote:

Please stop top posting. If you don't know what "top posting" means please refer to google.

You quoted my entire post below yours, but didn't answer any of the questions I asked. Why?

Sorry for my overlooking, I'm a newbie, and just cared about the question itself.
Sorry again, I just posted the detail info that leaded to the failure

Quote:

"return ok" Do you mean that it exits with a status of 0?

yeah, return 0, but no any "printf" related sentence.

Quote:

"null"? Does that mean an empty string or something else?

hum, may be blank, or \r or \n, but it is not the point

Quote:

This much I do understand, but I can't help you with the relevant information.

^_^, thanks for your attention, I guess what I mentioned above is really the key point to the issue. Maybe I could modify the command code to output the info towards a file or let it print the info too bu adding "printf" sentences.

I really appreciate your comments. Thanks again

catkin · 11-13-2009, 01:28 AM

One possibility is that the mystery program run by alarm_dbg that produces the desired output writes to terminal rather than stdout or stderr -- but the output would be seen on screen when the the script is run.

@vvpp: regards "hum, may be blank, or \r or \n, but it is not the point" that makes sense when you simply want to make your script work but it does not make sense when you are working with a volunteer who is trying to help you and needs all the available information in case it helps solve the problem.

Even if you think people are asking dumb questions it is smart to answer them. Answering people's questions keeps them happy. And you can't make your script work so do you know enough to decide what is a dumb question and what is a useful question?

Sometimes when trying to solve a difficult problem, the most crazy question can get the information that leads to a solution.