V10/man/man1/m4.1

.TH M4 1
.CT 1 prog_c
.SH NAME
m4 \(mi macro processor
.SH SYNOPSIS
.B m4
[
.I option ...
]
[
.I file ...
]
.SH DESCRIPTION
.I M4\^
is a macro processor
intended as a front end for C and other languages.
Each of the argument files is processed in order;
if there are no files, or if a file name is
.BR - ,
the standard input is read.
The processed text is written on the standard output.
.PP
The options and their effects are as follows:
.TP
.B -e
Operate interactively.
Interrupts are ignored and the output is unbuffered.
Using this mode requires a special state of mind.
.TP
.B -s
Enable line sync output for the C preprocessor,
.RB ( #line " .\|.\|.\|)"
.TP
.BI -B int\^
Change the size of the push-back and argument collection
buffers from the default of 4,096.
.TP
.BI -H int\^
Change the size of the symbol table hash array from the
default of 199.
The size should be prime.
.TP
.BI -S int\^
Change the size of the call stack from the default of 100 slots.
Macros take three slots, and non-macro arguments take one.
.TP
.BI -T int\^
Change the size of the token buffer from the default of 512 bytes.
.PP
The preceding options must appear before any
file names or
.B -D
or
.B -U
options.
.TP
\f5-D\fP\f2name\^\fP[\f5=\fP\f2val\^\fP]
Defines
.I name\^
to
.I val\^
or to null if
.I val
is missing.
.TP
.BI -U name\^
undefines
.IR name .
.PP
Macro calls
have the form:
.IP
.L name(arg1,arg2, .\|.\|., argn)
.PP
The
.B (
must immediately follow the name of the macro.
If a defined macro name is not followed by a
.BR ( ,
it is deemed to have no arguments.
Leading unquoted blanks, tabs, and new-lines are ignored while collecting arguments.
Potential macro names consist of alphabetic letters,
digits, and underscore
.BR _ ,
where the first character is not a digit.
.PP
Left and right single quotes are used to quote strings.
The value of a quoted string is the string stripped of the quotes.
.PP
When a macro name is recognized,
its arguments are collected by searching for a matching right
parenthesis.
Macro evaluation proceeds normally during the collection of the arguments,
and any commas or right parentheses
which happen to turn up within the value of a nested
call are as effective as those in the original input text.
After argument collection,
the value of the macro is pushed back onto the input stream
and rescanned.
.PP
The value of a macro is obtained by replacing
each occurrence of
.BI $ n\^
in the replacement text,
where
.I n\^
is a digit,
with the
.IR n -th
argument.
Argument 0 is the name of the macro;
missing arguments are replaced by the null string;
.B $#
is replaced by the number of arguments;
.B $*
is replaced by a list of all the arguments separated by commas;
.B $@
is like
.BR $* ,
but each argument is quoted (with the current quotes).
.PP
.I M4\^
makes available the following built-in macros.
They may be redefined, but once this is done the original meaning is lost.
Their values are null unless otherwise stated.
.TP 12
.B define
the second argument is installed as the replacement text of the macro
whose name is the first argument.
.TP
.B undefine
Remove the definition of the macro named in the argument.
.TP
.B defn
Return the quoted definition of the argument(s);
useful for renaming macros, especially built-ins.
.TP
.B pushdef
Like
.IR define ,
but save any previous definition.
.TP
.B popdef
Remove current definition of the argument(s),
exposing the previous one if any.
.TP
.B ifdef
If the first argument is defined, the value is the second argument, otherwise the third.
If there is no third argument, the value is null.
The word
.L unix\^
is predefined on
.SM UNIX
versions of
.IR m4 .
.TP
.B shift
Return all but the first argument.
The other arguments pushed back with
commas in between and quoted to
nullify the effect of the extra scan.
.TP
.B changequote
Change quote symbols to the first and second arguments.
The symbols may be up to five characters long.
.B Changequote\^
without arguments restores the original values
(i.e., 
.LR `\|' ).
.TP
.B changecom
Change left and right comment markers from the default
.B #
and new-line.
With no arguments, the comment mechanism is effectively
disabled.
With one argument, the left marker becomes the argument and
the right marker becomes new-line.
With two arguments, both markers are affected.
Comment markers may be up to five characters long.
.TP
.B divert
.I m4\^
Switch output to one of 10 streams,
numbered 0-9 designated by the argument.
The final output is the concatenation of the streams
in numerical order;
stream 0 is the current initially.
Output to a stream other than 0 through 9
is discarded.
.TP
.B undivert
Cause immediate output of text from diversions named as
arguments, or all diversions if no argument.
Text may be undiverted into another diversion.
Once undiverted, the diverted text is no longer contained in that diversion.
.TP
.B divnum
Return the name of the current output stream.
.TP
.B dnl
reads and discards characters up to and including the next new-line.
.TP
.B ifelse
If the first argument is the same string as the second,
then the value is the third argument.
If not, and if there are more than four arguments, the process is repeated with arguments 4, 5, 6 and 7.
Otherwise, the value is either the fourth string, or, if that is not present,
null.
.TP
.B incr
Return the value of the argument incremented by 1.
The value of the argument is calculated
by interpreting an initial digit-string as a decimal number.
.TP
.B decr
Return the value of the argument decremented by 1.
.TP
.B eval
Evaluate the argument as an arithmetic expression, using 32-bit arithmetic.
C-like operators include
.BR +-*/% ,
bitwise
.BR &|^~ ;
relationals; parentheses.
Octal and hex numbers may be specified as in C.
The second argument specifies the radix for the result;
the default is 10.
The third argument may be used to specify the minimum number
of digits in the result.
.TP
.B len
Returns the number of characters in the argument.
.TP
.B index
Return the position in the first argument where the second argument begins (zero origin),
or \-1 if the second argument does not occur.
.TP
.B substr
Return a substring of the first argument.
The second argument is a zero origin
number selecting the first character;
the third argument indicates the length of the substring.
A missing third argument is taken to be large enough to extend to
the end of the first string.
.TP
.B translit
Transliterate the characters in the first argument
from the set given by the second argument to the set given by the third,
deleting characters that lack a correspondent in the third set.
There is no character-range notation.
.TP
.B include
Return the contents of the file named in the argument.
.TP
.B sinclude
Same, but give no diagnostic if the file is inaccessible.
.TP
.B syscmd
Execute the
.SM UNIX
command given in the first argument.
No value is returned.
.TP
.B sysval
The return code from the last call to
.IR syscmd .
.TP
.B maketemp
Fill in a string of
.LR X
characters in the argument with the current process id.
.TP
.B m4exit
Exit immediately from
.IR m4 .
Argument 1, if given, is the exit code;
the default is 0.
.TP
.B m4wrap
Push the argument back at the end of the input.
Example:
.L m4wrap(`cleanup()')
.TP
.B errprint
Prints the argument
on the standard error file.
.TP
.B dumpdef
Print current names and definitions,
for the named items, or for all if no arguments are given.
.TP
.B traceon
If there are no arguments, turn on tracing for all macros
(including built-ins).
Otherwise, turn on tracing for named macros.
.TP
.B traceoff
Turn off trace globally and for any macros specified.
Macros specifically traced by
.B traceon\^
can be untraced only by specific calls to
.BR traceoff .
.SH EXAMPLES
.EX
define(fib,`ifelse(define(`n',eval($1))n,0,1,n,1,1,dnl()
`eval(fib(n-1)+fib($1-2))')')dnl()
fib(2*3)
.EE
.ns
.IP
Recursively evaluate a Fibonacci number.
The inner
.B define
avoids some reevaluations.