m4.html

unix 下的C开发手册,还用详细的例程。

to and including the next
newline
character.

<dt><b>dumpdef</b><dd>
The
<b>dumpdef</b>
macro writes the defined text to standard error for each of the macros
specified as arguments, or, if no arguments are specified, for all
macros.

<dt><b>errprint</b><dd>The
<b>errprint</b>
macro writes its arguments to standard error.

<dt><b>eval</b><dd>The
<b>eval</b>
macro evaluates its first argument as an
arithmetic expression, using 32-bit signed integer
arithmetic.
All of the C-language operators are supported, except for
[],
-&gt;,
++,
--,
(type)
unary *,
<b>sizeof</b>,
",", ".", "?:" and all assignment operators.
It is an error to specify any of these operators.
Precedence and associativity are as in C.
Systems support octal and
hexadecimal numbers as in C.
The second argument, if specified, sets the radix for the result;
the default is 10.
The third argument, if
specified, sets the minimum number of digits in the result.
It is an error to specify an argument
containing any non-numeric characters.


<dt><b>ifdef</b><dd>If the first argument to the
<b>ifdef</b>
macro is defined,
the defining text is the second argument.
Otherwise, the defining text is the third argument,
if specified, or the null string, if not.

<dt><b>ifelse</b><dd>If the first argument (or the defining text of the first
argument if it is a macro name) to the
<b>ifelse</b>
macro is the
same as the second argument (or the defining text of the
second argument if it is a macro name), then the defining
text is the third argument.
If there are more than four
arguments, the initial comparison of the first and second
arguments are repeated for each group of three arguments.
If no match is found, the defining text will be the argument
following the last set of three compared, otherwise it will be null.

<dt><b>include</b><dd>The defining text for the
<b>include</b>
macro is the contents
of the file named by the first argument.
It is an error if the file cannot be read.

<dt><b>incr</b><dd>The defining text of the
<b>incr</b>
macro is its first
argument incremented by 1.
It is an error to specify
an argument containing any non-numeric characters.

<dt><b>index</b><dd>The defining text of the
<b>index</b>
macro is the first character
position (as a string) in the first argument where a string
matching the second argument begins (zero origin), or -1 if
the second argument does not occur.

<dt><b>len</b><dd>The defining text of the
<b>len</b>
macro is the length (as a string)
of the first argument.

<dt><b>m4exit</b><dd>Exit from the
<i>m4</i>
utility.
If the first argument is
specified, it will be the exit code.
The default is zero.
It is an error to specify an argument
containing any non-numeric characters.

<dt><b>m4wrap</b><dd>The first argument will be processed when EOF is reached.
If the
<b>m4wrap</b>
macro is used multiple times, the arguments
specified will be processed in the order in which the
<b>m4wrap</b>
macros were processed.

<dt><b>maketemp</b><dd>
The defining text is the first argument, with any trailing
capital X characters replaced with the current process ID as a string.

<dt><b>popdef</b><dd>The
<b>popdef</b>
macro deletes the current definition of its
arguments, replacing it with the previous one.
If there is no previous definition, the macro is undefined.

<dt><b>pushdef</b><dd>
The
<b>pushdef</b>
macro is identical to the
<b>define</b>
macro with
the exception that it preserves any current definition
for future retrieval using the
<b>popdef</b>
macro.

<dt><b>shift</b><dd>The defining text for the
<b>shift</b>
macro is all of its arguments
except for the first one.

<dt><b>sinclude</b><dd>
The
<b>sinclude</b>
macro is identical to the
<b>include</b>
macro, except
that it is not an error if the file is inaccessible.

<dt><b>substr</b><dd>The defining text for the
<b>substr</b>
macro is the substring
of the first argument beginning at the zero-offset
character position specified by the second argument.
The third argument, if specified, is the number of characters
to select;
if not specified, the characters from the
starting point to the end of the first argument become
the defining text.
It is not an error to specify
a starting point beyond the end of the first argument and
the defining text will be null.
It is an error to
specify an argument containing any non-numeric characters.

<dt><b>syscmd</b><dd>The
<b>syscmd</b>
macro interprets its first argument as a shell command line.
The defining text is the string result of that command.
No output redirection is performed by the
<i>m4</i>
utility.
The exit status value from the command
can be retrieved using the
<b>sysval</b>
macro.


<dt><b>sysval</b><dd>The defining text of the
<b>sysval</b>
macro is the exit value
of the utility last invoked by the
<b>syscmd</b>
macro (as a string).

<dt><b>traceon</b><dd>The
<b>traceon</b>
macro enables tracing for the macros specified as
arguments, or, if no arguments are specified, for all macros.
The trace output is written to standard error
in an unspecified format.

<dt><b>traceoff</b><dd>The
<b>traceoff</b>
macro disables tracing for the macros specified as
arguments, or, if no arguments are specified, for all macros.

<dt><b>translit</b><dd>The defining text of the
<b>translit</b>
macro is the first
argument with every character that occurs in the second
argument replaced with the corresponding character from
the third argument.

<dt><b>undefine</b><dd>
The
<b>undefine</b>
macro deletes all definitions (including those
preserved using the
<b>pushdef</b>
macro) of the macros named
by its arguments.

<dt><b>undivert</b><dd>
The
<b>undivert</b>
macro causes immediate output of any text
in temporary buffers named as arguments, or all temporary
buffers if no arguments are specified.
Buffers can be
undiverted into other temporary buffers.
Undiverting
discards the contents of the temporary buffer.
It is an error to specify an argument containing any non-numeric characters.

</dl>
</blockquote><h4><a name = "tag_001_014_1321">&nbsp;</a>EXIT STATUS</h4><blockquote>
The following exit values are returned:
<dl compact>

<dt>0<dd>Successful completion.

<dt>&gt;0<dd>An error occurred

</dl>
<p>
If the
m4exit
macro is used, the exit value can be specified by the
input file.
</blockquote><h4><a name = "tag_001_014_1322">&nbsp;</a>CONSEQUENCES OF ERRORS</h4><blockquote>
Default.
</blockquote><h4><a name = "tag_001_014_1323">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
The
<b>defn</b>
macro is useful for renaming macros, especially built-ins.
</blockquote><h4><a name = "tag_001_014_1324">&nbsp;</a>EXAMPLES</h4><blockquote>
An example of a single
<i>m4</i>
input file capable of generating two output files follows.
The file
<b>file1.m4</b>
could contain lines such as:
<pre>
<code>
if(VER, 1, <i>do_something</i>)
if(VER, 2, <i>do_something</i>)
</code>
</pre>
<p>
The makefile for the program might include:
<pre>
<code>
file1.1.c : file1.m4
            m4 -D VER=1 file1.m4 &gt; file1.1.c
            ...
file1.2.c : file1.m4
            m4 -D VER=2 file1.m4 &gt; file1.2.c
            ...
</code>
</pre>
<br>
<p>
The
<b>-U</b>
option can be used to undefine
<b>VER</b>.
If
<b>file1.m4</b>
contains:
<pre>
<code>
if(VER, 1, <i>do_something</i>)
if(VER, 2, <i>do_something</i>)
ifndef(VER, <i>do_something</i>)
</code>
</pre>
<br>
then the makefile would contain:
<pre>
<code>
file1.0.c : file1.m4
            m4 -U VER file1.m4 &gt; file1.0.c
            ...
file1.1.c : file1.m4
            m4 -D VER=1 file1.m4 &gt; file1.1.c
            ...
file1.2.c : file1.m4
            m4 -D VER=2 file1.m4 &gt; file1.2.c
            ...
</code>
</pre>
</blockquote><h4><a name = "tag_001_014_1325">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_1326">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="c89.html">c89</a></i>.
</blockquote><hr size=2 noshade>
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