I have a database log ( db.log ) which the messages will be appended to it , some of the messages is non-useful , so I want to write a script to write all the lines that have the message "warning" to another log ( eg. db.log2 ), and then remove this line in db.log , as below example , can advise what can i do ? Thanks.


The log is as below
===================
#vi db.log

"
aaa
bbb
ccc
warning 111
ddd
eee
warning 222
fff
"



run the script , the desired output is as below
===============================================
#vi db.log
aaa
bbb
ccc
ddd
eee
fff


#vi db.log2
warning 111
warning 222

cat db.log | grep warning > warning-db.log
cat db.log | grep -v warning > no-warnings-db.log

warning-db.log - this would be the log file containing the warnings only.
no-warnings-db.log - this would be the log file minus the warnings.

Original log file remains untouched.

Actually, you don't need cat

Thx reply,

your method is simple , but I would like to keep the original file name of log to db.log , as if use your method , the file name would be changed .

The reason for do not want to change file name is because db.log is the standard file name , many users use this file name .

Thanks.

The problem is I'd expect db.log to be always (or most of the time) open & being written to by the db logger.
You shouldn't try to change the content if this is the case.
OTOH, if this is all after you've moved onto a new log file, then you can rename the no-warnings-db.log to db.log

Yes , the db.log is always read / open by user.

I want to update the db.log daily or weekly .