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<TITLE>Exim Filter Specification - Obeying commands conditionally</TITLE>
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<H2><A NAME="SEC19" HREF="filter_toc.html#TOC19">Obeying commands conditionally</A></H2>
<P>
Most of the power of filtering comes from the ability to test conditions and
obey different commands depending on the outcome. The <TT>`if'</TT> command is used to
specify conditional execution, and its general form is
<PRE>
if <<EM>condition</EM>>
then <<EM>commands</EM>>
elif <<EM>condition</EM>>
then <<EM>commands</EM>>
else <<EM>commands</EM>>
endif
</PRE>
<P>
There may be any number of <TT>`elif'</TT> and <TT>`then'</TT> sections (including none) and
the <TT>`else'</TT> section is also optional. Any number of commands, including nested
<TT>`if'</TT> commands, may appear in any of the <<EM>commands</EM>> sections.
</P>
<P>
Conditions can be combined by using the words <TT>`and'</TT> and <TT>`or'</TT>, and round
brackets (parentheses) can be used to specify how several conditions are to
combine. Without brackets, <TT>`and'</TT> is more binding than <TT>`or'</TT>.
<font color=green>
For example,
<PRE>
if
$h_subject: contains "Make money" or
$h_precedence: is "junk" or
($h_sender: matches ^\\d{8}@ and not personal) or
$message_body contains "this is spam"
then
seen finish
endif
</PRE>
<P>
</font>
A condition can be preceded by <TT>`not'</TT> to negate it, and there are also some
negative forms of condition that are more English-like.
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