Unable to capture required string from text file using Groovy - Jmeter JSR223 - regex

Question

I need to parse a text file testresults.txt and capture serial number and then write the captured serial number onto separate text file called serialno.txt using groovy Jmeter JSR223 post processor.
Below code is not working. It didn't get into the while loop itself. Kindly help.
import java.util.regex.Pattern
import java.util.regex.Matcher
String filecontent = new File("C:/device/resources/testresults.txt").text
def regex = "SerialNumber\" value=\"(.+)\""
java.util.regex.Pattern p = java.util.regex.Pattern.compile(regex)
java.util.regex.Matcher m = p.matcher(filecontent)
File SN = new File("C:/device/resources/serialno.txt")
while(m.find()) {
SN.write m.group(1)
}

Answer 1

If your code doesn't enter the loop it means that there are no matches so you need to amend your regular expression, you can use i.e. Regex101 website for experiments
Given the following content of the testresults.txt file:
SerialNumber" value="foo"
SerialNumber" value="bar"
SerialNumber" value="baz"
your code works fine.
For the time being I can only suggest using match operator to make your code more "groovy"
def source = new File('C:/device/resources/testresults.txt').text
def matches = (source =~ 'SerialNumber" value="(.+?)"')
matches.each { match ->
new File('C:/device/resources/serialno.txt') << match[1] << System.getProperty('line.separator')
}
Demo:
More information: Apache Groovy - Why and How You Should Use It