m4(1)m4(1)Namem4 - macro processor
Syntaxm4 [options] [files]
The macro processor is intended as a front end for Ratfor, C, and other
languages. Each of the argument files is processed in order; if there
are no arguments, or if an argument is hypen (-), 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 argu‐
ments take one.
-Tint Change the size of the token buffer from the default of
To be effective, these flags must appear before any file names and
before any -D or -U flags:
Defines name to val or to null in val's absence.
-Uname undefines name.
Macro calls have the following form:
name(arg1,arg2, . . . , argn)
The left parenthesis ( ( ) must immediately follow the name of the
macro. If a defined macro name is not followed by a left parenthesis,
it is deemed to have no arguments.
Leading unquoted blanks, tabs, and new lines are ignored while collect‐
ing arguments. Potential macro names consist of alphabetic letters,
digits, and underscore (_), where the first character is not a digit.
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 search‐
ing for a matching right parenthesis. Macro evaluation proceeds nor‐
mally 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
The makes available the following built-in macros. They may be rede‐
fined, but once this is done the original meaning is lost. Their val‐
ues 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 argu‐
ments 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
defn returns the quoted definition of its argument(s).
It is useful for renaming macros, especially built-
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 versions of
changequote Change quote characters to the first and second
arguments. The 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 The 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 out‐
put stream to its (digit-string) argument. Output
diverted to a stream other than 0 through 9 is dis‐
undivert causes immediate output of text from diversions
named as arguments, or all diversions if no argu‐
ment. Text may be undiverted into another diver‐
sion. 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,
incr returns the value of its argument incremented by 1.
The value of the argument is calculated by inter‐
preting an initial digit-string as a decimal num‐
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 argu‐
ment is taken to be large enough to extend to the
end of the first string.
shift is an unimplemented macro. Using shift generates
an error message.
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 per‐
include returns the contents of the file named in the argu‐
sinclude is identical to include, except that it says noth‐
ing if the file is inaccessible.
syscmd executes the UNIX command given in the first argu‐
ment. 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. For
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 speci‐
fied. Macros specifically traced by traceon can be
untraced only by specific calls to traceoff.
"The M4 Macro Processor," ULTRIX Supplementary Documents Vol. II:Pro‐