UNIX for Dummies Questions & Answers

Hi All,
I am a newbie,
I am looking for a script that can capture logs based on a request id and store it in tmp folder
Log files looks like this"

Code:

 - 2015-07-08 10:59:17,100 INFO   RequestId -> 923559008 Inside test method
 - 2015-07-08 10:59:17,100 INFO   RequestId -> 923559008 End of some test method method
 - 2015-07-08 10:59:17,100 INFO   RequestId -> 923559008 test test"

Trying to capture using Request id and request changes randomly, so it has to be a variable where i can set the value of the id and capture the logs in particular location.
Would really appreciate your help

Code:

var="123456789"
grep -w "$var" filename

Thanks CORONA,

to add to this, few more questions
Q1:How to capture from a different location where I am currently in
My Log file are in one location eg: Suppose the request id is printed in log file named as test_1.log and this is located in cd /servers/xxx/yyyy. and I am directory cd /tmp, so how to stay in cd /tmp and try to capture logs.
Q2: Where to create the executable script and the reply you posted what filename is it the filename of the outfile name? or filename i should use the file name from where i want to grab the request id?
Q3: Looking to execute the script from cd /tmp and get the output at same place in a form of log file which can be analyzed for results.

Thanks