Name
m4 - macroprocessor
Syntax
m4 [ options ] [ files ]
Description
The m4 command is a macroprocessor intended as a front end
for Ratfor, 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 4,096.
-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
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 open parentheses, (, must immediately follow the name of
the macro. If the name of a defined macro is not followed
by a close parenthese, (, 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.
The m4 command 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 some 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 (that is, `').
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 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 XXXXX in its argument with
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;
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.
See Also
cc(CP), cpp(CP).
Standards Conformance
m4 is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
and The X/Open Portability Guide II of January 1987.
(printed 6/18/89)