m4(1) General Commands Manual m4(1)
m4 - macro processor
m4 [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 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:
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 collecting 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 searching 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 and rescanned.
The makes available the following built-in macros. They may be redefined, 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; miss-
ing 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 argu-
ment, 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 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 argu-
ment. If not, and if there are more than four arguments, the process is repeated with arguments 4, 5, 6 and 7. Other-
wise, 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 +, -, *, /, %, ^ (expo-
nentiation), 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.
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 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 UNIX 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. For example:
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
traceoff turns off trace globally and for any macros specified. Macros specifically traced by traceon can be untraced only by
specific calls to traceoff.
"The M4 Macro Processor," ULTRIX Supplementary Documents Vol. II:Programmer