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20. Regular Expressions
20.1 Overview

JMeter includes the pattern matching software Apache Jakarta ORO

There is some documentation for this on the Jakarta web-site, for example a summary of the pattern matching characters

There is also documentation on an older incarnation of the product at OROMatcher User's guide , which might prove useful.

The pattern matching is very similar to the pattern matching in Perl. A full installation of Perl will include plenty of documentation on regular expressions - look for perlrequick, perlretut, perlre, perlreref.

It is worth stressing the difference between "contains" and "matches", as used on the Response Assertion test element:

  • "contains" means that the regular expression matched at least some part of the target, so 'alphabet' "contains" 'ph.b.' because the regular expression matches the substring 'phabe'.
  • "matches" means that the regular expression matched the whole target. So 'alphabet' is "matched" by 'al.*t'.

In this case, it is equivalent to wrapping the regular expression in ^ and $, viz '^al.*t$'.

However, this is not always the case. For example, the regular expression 'alp|.lp.*' is "contained" in 'alphabet', but does not match 'alphabet'.

Why? Because when the pattern matcher finds the sequence 'alp' in 'alphabet', it stops trying any other combinations - and 'alp' is not the same as 'alphabet', as it does not include 'habet'.

Note: unlike Perl, there is no need to (i.e. do not) enclose the regular expression in //.

So how does one use the modifiers ismx etc if there is no trailing /? The solution is to use extended regular expressions , i.e. /abc/i becomes (?i)abc. See also Placement of modifiers below.


20.2 Examples

Extract single string

Suppose you want to match the following portion of a web-page:

name="file" value="readme.txt">

and you want to extract readme.txt .

A suitable regular expression would be:

name="file" value="(.+?)">

The special characters above are:

  • ( and ) - these enclose the portion of the match string to be returned
  • . - match any character
  • + - one or more times
  • ? - don't be greedy, i.e. stop when first match succeeds

Note: without the ?, the .+ would continue past the first "> until it found the last possible "> - which is probably not what was intended.

Note: although the above expression works, it's more efficient to use the following expression:

name="file" value="([^"]+)"> where

[^"] - means match anything except "

In this case, the matching engine can stop looking as soon as it sees the first " , whereas in the previous case the engine has to check that it has found "> rather than say " > .

Extract multiple strings

Suppose you want to match the following portion of a web-page:

name="file.name" value="readme.txt" and you want to extract both file.name and readme.txt .

A suitable reqular expression would be:

name="([^"]+)" value="([^"]+)"

This would create 2 groups, which could be used in the JMeter Regular Expression Extractor template as $1$ and $2$.

The JMeter Regex Extractor saves the values of the groups in additional variables.

For example, assume:

  • Reference Name: MYREF
  • Regex: name="(.+?)" value="(.+?)"
  • Template: $1$$2$

Do not enclose the regular expression in / /

The following variables would be set:

  • MYREF: file.namereadme.txt
  • MYREF_g0: name="file.name" value="readme.txt"
  • MYREF_g1: file.name
  • MYREF_g2: readme.txt
These variables can be referred to later on in the JMeter test plan, as ${MYREF}, ${MYREF_g1} etc


20.3 Line mode

The pattern matching behaves in various slightly different ways, depending on the setting of the multi-line and single-line modifiers. Note that the single-line and multi-line operators have nothing to do with each other; they can be specified independently.

Single-line mode

Single-line mode only affects how the '.' meta-character is interpreted.

Default behaviour is that '.' matches any character except newline. In single-line mode, '.' also matches newline.

Multi-line mode

Multi-line mode only affects how the meta-characters '^' and '$' are interpreted.

Default behaviour is that '^' and '$' only match at the very beginning and end of the string. When Multi-line mode is used, the '^' metacharacter matches at the beginning of every line, and the '$' metacharacter matches at the end of every line.


20.4 Meta characters

Regular expressions use certain characters as meta characters - these characters have a special meaning to the RE engine. Such characters must be escaped by preceeding them with \ (backslash) in order to treat them as ordinary characters. Here is a list of the meta characters and their meaning (please check the ORO documentation if in doubt).

  • ( ) - grouping
  • [ ] - character classes
  • { } - repetition
  • * + ? - repetition
  • . - wild-card character
  • \ - escape character
  • | - alternatives
  • ^ $ - start and end of string or line

Please note that ORO does not support the \Q and \E meta-characters. [In other RE engines, these can be used to quote a portion of an RE so that the meta-characters stand for themselves.]

The following Perl5 extended regular expressions are supported by ORO.

(?#text)
An embedded comment causing text to be ignored.
(?:regexp)
Groups things like "()" but doesn't cause the group match to be saved.
(?=regexp)
A zero-width positive lookahead assertion. For example, \w+(?=\s) matches a word followed by whitespace, without including whitespace in the MatchResult.
(?!regexp)
A zero-width negative lookahead assertion. For example foo(?!bar) matches any occurrence of "foo" that isn't followed by "bar". Remember that this is a zero-width assertion, which means that a(?!b)d will match ad because a is followed by a character that is not b (the d) and a d follows the zero-width assertion.
(?imsx)
One or more embedded pattern-match modifiers. i enables case insensitivity, m enables multiline treatment of the input, s enables single line treatment of the input, and x enables extended whitespace comments.
Note that (?<=regexp) - lookbehind - is not supported.


20.5 Placement of modifiers

Modifiers can be placed anywhere in the regex, and apply from that point onwards. [A bug in ORO means that they cannot be used at the very end of the regex. However they would have no effect there anyway.]

The single-line (?s) and multi-line (?m) modifiers are normally placed at the start of the regex.

The ignore-case modifier (?i) may be usefully applied to just part of a regex, for example:


Match ExAct case or (?i)ArBiTrARY(?-i) case



20.6 Testing Regular Expressions

There is a demo applet for Apache JMeter ORO.

Another approach is to use a simple test plan to test the regular expressions. The Java Request sampler can be used to generate a sample, or the HTTP Sampler can be used to load a file. Add a Debug Sampler and a Tree View Listener and changes to the regular expression can be tested quickly, without needing to access any external servers.




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