m4(1) SDK R4.11 m4(1)
NAME
m4 - macro processor
SYNOPSIS
m4 [ options ] [ files ]
DESCRIPTION
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 -, the standard input is
read. The processed text is written on the standard output.
The options and their effects are as follows:
-e Operate interactively. Interrupts are ignored and the output
is unbuffered.
-s Enable line sync output for the C preprocessor (#line ...)
-Bint Change the size of the push-back and argument collection
buffers from the default of 4096.
-Hint Change the size of the symbol table hash array from the
default of 199. The size should be prime.
-Sint Change the size of the call stack from the default size of 100
slots. Macros take three slots, and non-macro arguments take
one.
-Tint Change the size of the token buffer from the default of 512
bytes.
To be effective, these flags must appear before any file names and
before any -D or -U flags:
-Dname[=val]
Defines name to val or to null in val's absence.
-Uname undefines name.
Macro calls have the form:
name(arg1,arg2, ..., argn)
The ( must immediately follow the name of the macro. If the name of
a defined macro is not followed by a (, it is deemed to be a call of
that macro with no arguments. Potential macro names consist of
alphabetic letters, digits, and underscore (), where the first
character is not a digit.
Leading unquoted blanks, tabs, and new-lines are ignored while
collecting arguments. Left and right single quotes are used to quote
strings. The value of a quoted string is the string stripped of the
quotes.
When a macro name is recognized, its arguments are collected by
searching for a matching right parenthesis. If fewer arguments are
supplied than are in the macro definition, the trailing arguments are
taken to be null. 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.
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.
define the second argument is installed as the value of the
macro whose name is the first argument. Each occurrence
of $n in the replacement text, where n is a digit, is
replaced by the n-th argument. Argument 0 is the name of
the macro; missing arguments are replaced by the null
string; $# is replaced by the number of arguments; $* is
replaced by a list of all the arguments separated by
commas; $@ is like $*, but each argument is quoted (with
the current quotes).
undefine removes the definition of the macro named in its
argument.
defn returns the quoted definition of its argument(s). It is
useful for renaming macros, especially built-ins.
pushdef like define, but saves any previous definition.
popdef removes current definition of its argument(s), exposing
the previous one, if any.
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 unix is predefined
on UNIX system versions of m4.
shift returns all but its first argument. The other arguments
are quoted and pushed back with commas in between. The
quoting nullifies the effect of the extra scan that will
subsequently be performed.
changequote change quote symbols to the first and second arguments.
The symbols may be up to five characters long.
Changequote without arguments restores the original
values (i.e., `').
changecom change left and right comment markers from the default #
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.
divert m4 maintains 10 output streams, numbered 0-9. The final
output is the concatenation of the streams in numerical
order; initially stream 0 is the current stream. The
divert macro changes the current output stream to its
(digit-string) argument. Output diverted to a stream
other than 0 through 9 is discarded.
undivert causes immediate output of text from diversions named as
arguments, or all diversions if no argument. Text may be
undiverted into another diversion. Undiverting discards
the diverted text.
divnum returns the value of the current output stream.
dnl reads and discards characters up to and including the
next new-line.
ifelse has three or more arguments. 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 it is not present, null.
incr returns the value of its argument incremented by 1. The
value of the argument is calculated by interpreting an
initial digit-string as a decimal number.
decr returns the value of its argument decremented by 1.
eval evaluates its argument as an arithmetic expression, using
32-bit arithmetic. Operators include +, -, *, /, %, ^
(exponentiation), bitwise &, |, ^, and ~; 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.
len returns the number of characters in its argument.
index returns the position in its first argument where the
second argument begins (zero origin), or -1 if the second
argument does not occur.
substr returns a substring of its 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.
translit transliterates the characters in its first argument from
the set given by the second argument to the set given by
the third. No abbreviations are permitted.
include returns the contents of the file named in the argument.
sinclude is identical to include, except that it says nothing if
the file is inaccessible.
syscmd executes the DG/UX system command given in the first
argument. No value is returned.
sysval is the return code from the last call to syscmd.
maketemp fills in a string of XXXXXX at the end of its argument
with a unique letter and the current process ID.
m4exit causes immediate exit from m4. Argument 1, if given, is
the exit code; the default is 0.
m4wrap argument 1 will be pushed back at final EOF so that it
gets evaluated last. Example: m4wrap('cleanup()')
errprint prints its argument on the diagnostic output file.
dumpdef prints current names and definitions, for the named
items, or for all if no arguments are given.
traceon with no arguments, turns on tracing for all macros
(including built-ins). Otherwise, turns on tracing for
named macros.
traceoff turns off trace globally and for any macros specified.
Macros specifically traced by traceon can be untraced
only by specific calls to traceoff.
EXAMPLE
m4 file1 file2 > outputfile
will run the m4 macro processor on the files file1 and file2,
redirecting the output into outputfile.
SEE ALSO
cc(1), cpp(1).
The M4 Macro Processor by B. W. Kernighan and D. M. Ritchie.
Licensed material--property of copyright holder(s)