1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
|
<HTML>
<HEAD>
<!-- This HTML file has been created by texi2html 1.52
from filter on 25 November 2000 -->
<TITLE>Exim Filter Specification - More about string expansion</TITLE>
</HEAD>
<body bgcolor="#FFFFFF" text="#00005A" link="#FF6600" alink="#FF9933" vlink="#990000">
Go to the <A HREF="filter_1.html">first</A>, <A HREF="filter_29.html">previous</A>, <A HREF="filter_31.html">next</A>, <A HREF="filter_34.html">last</A> section, <A HREF="filter_toc.html">table of contents</A>.
<P><HR><P>
<H2><A NAME="SEC30" HREF="filter_toc.html#TOC30">More about string expansion</A></H2>
<P>
The description which follows in the next section is an excerpt from the full
specification of Exim, except that it lists only those expansion variables that
are likely to be useful in filter files.
</P>
<P>
Expanded strings are copied verbatim from left to right except when a dollar or
backslash character is encountered. A dollar specifies the start of a portion
of the string which is interpreted and replaced as described below.
</P>
<P>
An uninterpreted dollar can be included in the string by putting a backslash in
front of it -- if the string appears in quotes, two backslashes are required
because the quotes themselves cause interpretation of backslashes when the
string is read in. A backslash can be used to prevent any special character
being treated specially in an expansion, including itself.
</P>
<P>
A backslash followed by one of the letters `n', `r', or `t' is recognized as an
escape sequence for the character newline, carriage return, or tab,
respectively. A backslash followed by up to three octal digits is recognized as
an octal encoding for a single character, while a backslash followed by `x' and
up to two hexadecimal digits is a hexadecimal encoding. A backslash followed by
any other character causes that character to be added to the output string
uninterpreted. These escape sequences are also recognized in quoted strings as
they are read in; their interpretation in expansions as well is useful for
unquoted strings and other cases such as looked-up strings that are then
expanded.
</P>
<P><HR><P>
Go to the <A HREF="filter_1.html">first</A>, <A HREF="filter_29.html">previous</A>, <A HREF="filter_31.html">next</A>, <A HREF="filter_34.html">last</A> section, <A HREF="filter_toc.html">table of contents</A>.
</BODY>
</HTML>
|
