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<!DOCTYPE document
[
<!ENTITY sect-num '20'>
]>
<document prev="functions.html" next="hints_and_tips.html" id="$Id: regular_expressions.xml 1175606 2011-09-25 22:28:22Z sebb $">
<properties>
<title>User's Manual: Regular Expressions</title>
</properties>
<body>
<section name="&sect-num;. Regular Expressions" anchor="regex">
<subsection name="&sect-num;.1 Overview" anchor="overview">
<p>
JMeter includes the pattern matching software <a href="http://jakarta.apache.org/oro/">Apache Jakarta ORO</a>
<br/>
There is some documentation for this on the Jakarta web-site, for example
<a href="http://jakarta.apache.org/oro/api/org/apache/oro/text/regex/package-summary.html">
a summary of the pattern matching characters</a>
</p>
<p>
There is also documentation on an older incarnation of the product at
<a href="http://www.savarese.org/oro/docs/OROMatcher/index.html">OROMatcher User's guide</a>, which might prove useful.
</p>
<p>
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.
</p>
<p>
It is worth stressing the difference between "contains" and "matches", as used on the Response Assertion test element:
</p>
<ul>
<li>
"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'.
</li>
<li>
"matches" means that the regular expression matched the whole target.
So 'alphabet' is "matched" by 'al.*t'.
</li>
</ul>
<p>In this case, it is equivalent to wrapping the regular expression in ^ and $, viz '^al.*t$'.
</p>
<p>However, this is not always the case.
For example, the regular expression 'alp|.lp.*' is "contained" in 'alphabet', but does not match 'alphabet'.
</p>
<p>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'.
</p>
<p>
Note: unlike Perl, there is no need to (i.e. do not) enclose the regular expression in //.
</p>
<p>
So how does one use the modifiers ismx etc if there is no trailing /?
The solution is to use <i>extended regular expressions</i>, i.e. /abc/i becomes (?i)abc.
See also <a href="placement">Placement of modifiers</a> below.
</p>
</subsection>
<subsection name="&sect-num;.2 Examples" anchor="examples">
<h3>Extract single string</h3>
<p>
Suppose you want to match the following portion of a web-page:
<br/>
<code>name="file" value="readme.txt"></code>
<br/>
and you want to extract <code>readme.txt</code>.
<br/>
A suitable regular expression would be:
<br/>
<code>name="file" value="(.+?)"></code>
<p>
The special characters above are:
</p>
<ul>
<li>( and ) - these enclose the portion of the match string to be returned</li>
<li>. - match any character</li>
<li>+ - one or more times</li>
<li>? - don't be greedy, i.e. stop when first match succeeds</li>
</ul>
<p>
Note: without the ?, the .+ would continue past the first <code>"></code>
until it found the last possible <code>"></code> - which is probably not what was intended.
</p>
<p>
Note: although the above expression works, it's more efficient to use the following expression:
<br/>
<code>name="file" value="([^"]+)"></code>
where<br></br>
[^"] - means match anything except "<br></br>
In this case, the matching engine can stop looking as soon as it sees the first <code>"</code>,
whereas in the previous case the engine has to check that it has found <code>"></code> rather than say <code>" ></code>.
</p>
<h3>Extract multiple strings</h3>
<p>
Suppose you want to match the following portion of a web-page:<br/>
<code>name="file.name" value="readme.txt"</code>
and you want to extract both <code>file.name</code> and <code>readme.txt</code>.
<br/>
A suitable reqular expression would be:
<br/>
<code>name="([^"]+)" value="([^"]+)"</code>
<br/>
This would create 2 groups, which could be used in the JMeter Regular Expression Extractor template as $1$ and $2$.
</p>
<p>
The JMeter Regex Extractor saves the values of the groups in additional variables.
</p>
<p>
For example, assume:
</p>
<ul>
<li>Reference Name: MYREF</li>
<li>Regex: name="(.+?)" value="(.+?)"</li>
<li>Template: $1$$2$</li>
</ul>
<note>Do not enclose the regular expression in / /</note>
<p>
The following variables would be set:
</p>
<ul>
<li>MYREF: file.namereadme.txt</li>
<li>MYREF_g0: name="file.name" value="readme.txt"</li>
<li>MYREF_g1: file.name</li>
<li>MYREF_g2: readme.txt</li>
</ul>
These variables can be referred to later on in the JMeter test plan, as ${MYREF}, ${MYREF_g1} etc
</p>
</subsection>
<subsection name="&sect-num;.3 Line mode" anchor="line_mode">
<p>The pattern matching behaves in various slightly different ways,
depending on the setting of the multi-line and single-line modifiers.
Note that the single-line and multi-line operators have nothing to do with each other;
they can be specified independently.
</p>
<h3>Single-line mode</h3>
<p>
Single-line mode only affects how the '.' meta-character is interpreted.
</p>
<p>
Default behaviour is that '.' matches any character except newline.
In single-line mode, '.' also matches newline.
</p>
<h3>Multi-line mode</h3>
<p>
Multi-line mode only affects how the meta-characters '^' and '$' are interpreted.
</p>
<p>
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.</p>
</subsection>
<subsection name="&sect-num;.4 Meta characters" anchor="meta_chars">
<p>
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).
</p>
<ul>
<li>( ) - grouping</li>
<li>[ ] - character classes</li>
<li>{ } - repetition</li>
<li>* + ? - repetition</li>
<li>. - wild-card character</li>
<li>\ - escape character</li>
<li>| - alternatives</li>
<li>^ $ - start and end of string or line</li>
</ul>
<p>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.]</p>
<p>
The following Perl5 extended regular expressions are supported by ORO.
<dl>
<dt>(?#text)</dt>
<dd>An embedded comment causing text to be ignored.</dd>
<dt>(?:regexp)</dt>
<dd>Groups things like "()" but doesn't cause the group match to be saved.</dd>
<dt>(?=regexp)</dt>
<dd>A zero-width positive lookahead assertion. For example, \w+(?=\s) matches a word followed by whitespace, without including whitespace in the MatchResult.</dd>
<dt>(?!regexp)</dt>
<dd>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.</dd>
<dt>(?imsx)</dt>
<dd>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.</dd>
</dl>
<b>Note that <code>(?&lt;=regexp)</code> - lookbehind - is not supported.</b>
</p>
</subsection>
<subsection name="&sect-num;.5 Placement of modifiers" anchor="placement">
<p>
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.]
</p>
<p>
The single-line (?s) and multi-line (?m) modifiers are normally placed at the start of the regex.
</p>
<p>
The ignore-case modifier (?i) may be usefully applied to just part of a regex,
for example:
<pre>
Match ExAct case or (?i)ArBiTrARY(?-i) case
</pre>
</p>
</subsection>
</section>
<section name="&sect-num;.6 Testing Regular Expressions" anchor="testing_expressions">
<p>
Since JMeter 2.4, the listener <a href="component_reference.html#View_Results_Tree">View Results Tree</a>
include a RegExp Tester to test regular expressions directly on sampler response data.
</p>
<p>
There is a <a href="http://jakarta.apache.org/oro/demo.html">demo</a> applet for Apache JMeter ORO.
</p>
<p>
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.
</p>
</section>
</body>
</document>
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