/usr/share/doc/mailutils-doc/mailutils.html/Lexical-Structure.html

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<title>GNU Mailutils Manual: Lexical Structure</title>

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<a name="Lexical-Structure"></a>
<div class="header">
<p>
Next: <a href="Syntax.html#Syntax" accesskey="n" rel="next">Syntax</a>, Up: <a href="Sieve-Language.html#Sieve-Language" accesskey="u" rel="up">Sieve Language</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Lexical-Structure-1"></a>
<h3 class="section">5.1 Lexical Structure</h3>

<a name="Whitespace-and-Comments"></a>
<h4 class="subheading">Whitespace and Comments</h4>

<p>Comments are semantically equivalent to whitespace and can be used
anyplace that whitespace is (with one exception in multi-line strings,
as described below).
</p>
<p>There are two kinds of comments: hash comments, that begin with a
&lsquo;<samp>#</samp>&rsquo; character that is not contained within a string and continue
until the next newline, and C-style or bracketed comments, that are
delimited by &lsquo;<samp>/*</samp>&rsquo; and &lsquo;<samp>*/</samp>&rsquo; tokens.  The bracketed comments
may span multiple lines.  E.g.:
</p>
<div class="smallexample">
<pre class="smallexample">if size :over 100K
  { # this is a comment
    discard;
  }
  
if size :over 100K
  { /* this is a comment
       this is still a comment */ discard /* this is a comment again
     */ ;
  }
</pre></div>

<p>Like in C, bracketed comments do not nest.
</p>
<a name="Lexical-Tokens"></a>
<h4 class="subheading">Lexical Tokens</h4>

<p>The basic lexical entities are <em>identifiers</em> and <em>literals</em>.
</p>
<p>An <em>identifier</em> is a sequence of letters, digits and underscores,
that begins with a letter or underscore.  For example, <code>header</code> and
<code>check_822_again</code> are valid identifiers, whereas <code>1st</code> is not.
A special form of identifier is <em>tag</em>: it is an identifier prefixed
with a colon (&lsquo;<samp>:</samp>&rsquo;), e.g.: <code>:comparator</code>. 
</p>
<p>A <em>literal</em> is a data that is not executed, merely evaluated &ldquo;as
is&rdquo;, to be used as arguments to commands.  There are four kinds of
literals:
</p>
<ul>
<li> Number
<a name="index-numbers_002c-sieve"></a>

<p><em>Numbers</em> are given as ordinary unsigned decimal numbers.  An
optional suffix may be used to indicate a multiple of a power of two.
The suffixes are: &lsquo;<samp>K</samp>&rsquo; specifying &ldquo;kibi-&rdquo;, or 1,024 (2^10) times
the value of the number; &lsquo;<samp>M</samp>&rsquo; specifying &ldquo;mebi-&rdquo;, or 1,048,576
(2^20) times the value of the number; and &lsquo;<samp>G</samp>&rsquo; specifying &ldquo;tebi-&rdquo;,
or 1,073,741,824 (2^30) times the value of the number.
</p>
<p>The numbers have 32 bits of magnitude.
</p>
</li><li> String
<a name="index-strings_002c-sieve"></a>
A <em>string</em> is any sequence of characters enclosed in double quotes
(&lsquo;<samp>&quot;</samp>&rsquo;).  A string cannot contain newlines and double quote
characters.  This limitation will disappear in future releases.

</li><li> Multiline Strings
<a name="index-multiline-strings_002c-sieve"></a>
<a name="index-text_003a"></a>
A <em>multiline string</em> is used to represent large blocks of text
with embedded newlines and special characters.  It starts with the
keyword <code>text:</code> followed by a newline and ends with a dot
(&lsquo;<samp>.</samp>&rsquo;) on a newline by itself.  Any characters between these two
markers are taken verbatim.  For example:

<div class="smallexample">
<pre class="smallexample">text:
** This is an automatic response from my message **
** filtering program.                            **

I can not attend your message right now.  However it
will be saved, and I will read it as soon as I am back.

Regards,
Fred
.
</pre></div>

<p>Notice that a hashed comment or whitespace may occur between
<code>text:</code> and the newline.  However, when used inside the multiline
string a hash sign looses its special meaning (except in one case, see
below) and is taken as is, as well as bracketed comment delimiters.
In other words, no comments are allowed within a multiline string.  E.g.:
</p>    
<div class="smallexample">
<pre class="smallexample">text: # This is a comment

Sample text
# This line is taken verbatim
/* And this line too */
.
</pre></div>

<p>The only exception to this rule is that preprocessor <code>include</code>
statement is expanded as usual when found within a multiline string
(see <a href="Preprocessor.html#Preprocessor">Preprocessor</a>), e.g.:
</p>
<div class="smallexample">
<pre class="smallexample">text:
#include &lt;myresponse.txt&gt;
.
</pre></div>

<p>This results in the contents of file <samp>myresponse.txt</samp> being read
and interpreted as the contents of the multiline string.
</p>
<p>GNU libmu_sieve extends the described syntax as follows.  If the keyword
<code>text:</code> is immediately followed by a dash (&lsquo;<samp>-</samp>&rsquo;), then all
leading tab characters are stripped from input lines and the line
containing delimiter (&lsquo;<samp>.</samp>&rsquo;).  This allows multiline strings within
scripts to be indented in a natural fashion.
</p>
<p>Furthermore, if the <code>text:</code> (optionally followed by &lsquo;<samp>-</samp>&rsquo;) is
immediately followed by a word, this word will be used as ending
delimiter of multiline string instead of the default dot.  For
example:        
</p>
<div class="smallexample">
<pre class="smallexample">if header &quot;from&quot; &quot;me@example.com&quot;
  {
    reject text:-EOT
        I do not accept messages from
        this address.
        .
        .
        EOT
     # Notice that this the multiline string ends here.
     # The single dots above will be part of it.
    ;
  }
</pre></div>

</li><li> String Lists
<a name="index-string-list_002c-sieve"></a>

<p>A <em>string list</em> is a comma-delimited list of quoted strings, enclosed
in a pair of square brackets, e.g.:
</p>
<div class="smallexample">
<pre class="smallexample">[&quot;me@example.com&quot;, &quot;me00@landru.example.edu&quot;]
</pre></div>

<p>For convenience, in any context where a list of strings is appropriate,
a single string is allowed without being a member of a list: it is
equivalent to a list with a single member.  For example, the following
two statements are equivalent:
</p>
<div class="smallexample">
<pre class="smallexample">exists &quot;To&quot;;
exists [&quot;To&quot;];
</pre></div>

</li></ul>

<hr>
<div class="header">
<p>
Next: <a href="Syntax.html#Syntax" accesskey="n" rel="next">Syntax</a>, Up: <a href="Sieve-Language.html#Sieve-Language" accesskey="u" rel="up">Sieve Language</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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