Using Regular Expression Extractor in JMeter
In this tutorial, learn what the regular expression extractor is for, and how to use it with JMeter to capture dynamic values.
The regular expression extractor is used to capture the dynamic data- from the response header or body, from the main sample or subsamples, or even from another JMeter variable- and store it into a variable for future use. It allows the user to extract values from a server response using a Perl-type regular expression. As a post-processor, this element will execute after each Sample request in its scope, applying the regular expression, extracting the requested values, generating the template string, and storing the result in the given variable name.
How to Use Regular Expression Extractor to Capture Dynamic Values
If the match number is set to a non-negative number, and a match occurs, the variables are set as follows:
refName – the value of the template
refName_gn, where n=0,1,2 – the groups for the match
- refName_g – the number of groups in the Regex (excluding 0)
If no match occurs, then the refName variable is set to the default (unless this is absent). Also, the following variables are removed:
refName_g0
refName_g1
- refName_g
If the match number is set to a negative number, then all the possible matches in the sampler data are processed. The variables are set as follows:
refName_matchNr – the number of matches found; could be 0
refName_n, where n = 1, 2, 3 etc. – the strings as generated by the template
refName_n_gm, where m=0, 1, 2 – the groups for match n
refName – always set to the default value
- refName_gn – not set
Note that the refName variable is always set to the default value in this case, and the associated group variables are not set.
To verify the regular expression, we can use either regular expression tester from JMeter itself, or we have a good website to validate the regular expression, www.regexpal.com.
| Character classes | |
|---|---|
| . | any character except newline |
| \w \d \s | word, digit, whitespace |
| \W \D \S | not word, digit, whitespace |
| [abc] | any of a, b, or c |
| [^abc] | not a, b, or c |
| [a-g] | character between a & g |
| Anchors | |
| ^abc$ | start / end of the string |
| \b | word boundary |
| Escaped characters | |
| \. \* \\ | escaped special characters |
| \t \n \r | tab, linefeed, carriage return |
| \u00A9 | unicode escaped © |
| Groups & Lookaround | |
| (abc) | capture group |
| \1 | backreference to group #1 |
| (?:abc) | non-capturing group |
| (?=abc) | positive lookahead |
| (?!abc) | negative lookahead |
Practical Exposure
If the request parameters contain multiple values as mentioned below, we have to capture all the values and subsequently pass them.
We have to give the match number attribute as -1 to capture all the values in the reference name, as below:
If the match number is set to a negative number, then all the possible matches in the sampler data are processed. The variables are set as follows:
refName_matchNr – the number of matches found; could be 0
refName_n, where n = 1, 2, 3 etc. – the strings as generated by the template
refName_n_gm, where m=0, 1, 2 – the groups for match n
refName – always set to the default value
- refName_gn – not set
Note that the refName variable is always set to the default value in this case, and the associated group variables are not set.
Bookid_matchNr gives the total number of matches; in this example, it is shown as 4:
Opinions expressed by DZone contributors are their own.