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<!DOCTYPE document
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<document prev="functions.html" next="glossary.html" date="$Date: 2008-05-12 23:26:26 +0100 (Mon, 12 May 2008) $">

<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">
<p>
Extract single string
<br/>
Suppose you want to match the following portion of a web-page: 
<br/>
name="file" value="readme.txt" and you want to extract readme.txt.
<br/>
A suitable reqular expression would be:
<br/>
name="file" value="(.+?)"
<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. + - one or more times. 
? - don't be greedy, i.e. stop when first match succeeds</li>
</ul>
<p>
Note: without the ?, the .+ would continue past the first " until it found the last possible " - probably not what was intended.
</p>
<p>Extract multiple strings</p>

Suppose you want to match the following portion of a web-page: name="file.name" value="readme.txt" and you want to extract file.name and readme.txt.
<br/>
A suitable reqular expression would be:
<br/>
name="(.+?)" value="(.+?)"
<br/>
This would create 2 groups, which could be used in the JMeter Regular Expression Extractor template as $1$ and $2$.
<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>
</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>

</body>
</document>
