Parsing and Storing parts or paragraphs of log file

At many times we need to parse and store parts of a log file. Suppose an error log, you would like to parse all errors. If the errors span only one line, you could use a grep.

But if the errors span multiple lines ... you need to put a little logic into your script. There are many ways to do this, but this script that i post here is more readable and can be modified to other's requirement.

Link to the code
Link to a sample input

In the example script i am parsing an error log (named 'input.txt'). The script stores all lines that start with "SQL0204N" till it finds an empty line. Likewise it extracts all errors, even if the error messages span multiple lines.