I have log coming in this format. this value is dynamic and keep changing in terms of Form and numbers
Counts=[100A=10,100B=1,100C=2,100D=1,100E=3,100A=20,100B=1,100C=2,100D=1,100E=3]
I want to calculate
100A=30
100B=2
100C=4
100D=2
100E=6
I have ask similar question where I have different requirements
http://answers.splunk.com/answers/185780/multi-pattern-string-calculation-on-fields.html
I think you want to use extract(kv). This should give you fields for any dynamic range of files in the counts field
...| rex "Counts=\[(?<Counts>[^\]]+)\]" | field _time Counts|extract pairdelim="," kvdelim="=" | fields _time 100* | stats count(*) as * by _time