Powershell script to parse a log file and then append to a file - linux

Question

I am new to Shellscripting.I am working on a poc in which a script should read a log file and then append to a existing file for the purpose of alert.It should work as per below
There will be some predefined format according to which it will decide whether to append in file or not.For example:
WWXXX9999XS message
**XXX** - is a 3 letter acronym (application code) like for **tom** for tomcat application
9999 - is a 4 numeric digit in the range 1001-1999
**E or X** - For notification X ,If open/active alerts already existing for same error code and same message,new alerts will not be raised for existing one.Once you have closed existing alerts,it will raise alarm for new error.There is any change in message for same error code from existing one, it will raise a alarm even though open/active alerts present.
X option is only for drop duplicates on code and message otherwise all alert mechanisms are same.
**S** - is the severity level, I.e 2,3
**message** - is any text that will be displayed
The script will examine the log file, and look for error like cloud server is down,then it would append 'wwclo1002X2 cloud server is down'if its a new alert.
2.If the same alert is coming again,then it should append 'wwclo1002E2 cloud server is down

Answer 1

There are some very handy commands you can use to do this type of File manipulation. I've updated this in response to your comment to allow functionality that will check if the error has already been appended to the new file.
My suggestion would be that there is enough functionality here to warrant saving it in a bash script.
My approach would be to use a combination of less, grep and > to read and parse the file and then append to the new file. First save the following into a bash script (e.g. a file named script.sh)
#!/bin/bash
result=$(less $1 | grep $2)
exists=$(less $3 | grep $2)
if [[ "$exists" == "$result" ]]; then
echo "error, already present in file"
exit 1
else
echo $result >> $3
exit 0
fi
Then use this file in the command passing in the log file as the first argument, the string to search for as the second argument and the target results file as the third argument like this:
./script.sh <logFileName> "errorToSearchFor" <resultsTargetFileName>
Don't forget to run the file you will need to change the permissions - you can do this using:
chmod u+x script.sh
Just to clarify as you have mentioned you are new to scripting - the less command will output the entire file, the | command (an unnamed pipe) will pass this output to the grep command which will then search the file for the expression in quotes and return all lines from the file containing that expression. The output of the grep command is then appended to the new file with >>.
You may need to tailor the expression in quotes after grep to get exactly the output you want from the log file.
The filenames are just placeholders, be sure to update these with the correct file names. Hope this helps!
Note updated > to >> (single angle bracket overwrites, double angle bracket appends