M4(1)M4(1)NAMEm4 - macro processor
SYNOPSISm4 [ -Dname=value ] [ -Qname=value ] [ -Uname ] [ file ... ]
DESCRIPTION
M4 is a general-purpose macro processor. It copies text from each of
the input files in order (or standard input by default), and writes the
processed text to the standard output.
Macro calls have the form
name(arg1, arg2, ..., argn)
The `(' must immediately follow the name of the macro. If a defined
macro name is not followed by a `(', it is deemed to have no arguments.
Leading unquoted blanks, tabs, and newlines are ignored while collect‐
ing arguments. A comma within a nested parenthesis is part of an argu‐
ment value, not an argument separator. Potential macro names consist
of alphabetic letters, Unicode characters, digits, and underscore `_',
where the first character is not a digit.
Comments begin with the # character and extend to the end of that line;
the characters in a comment are copied to the current output stream
unchanged. The comment start and end sequences may be changed using
the changecom call described below.
The left and right single quotes (ie, grave and acute accents `´ ) are
used to quote strings. Because the left and right quotes are distinct,
quoted strings may nest. The value of a quoted string is the string
stripped of the outermost quotes. The left and right quote characters
may be changed using the changequote call described below.
When m4 recognises a macro name, followed by a `(', it collects argu‐
ments up to a matching right parenthesis. Macro evaluation proceeds
normally during this collection, and the text produced by those macro
calls is interpreted exactly as if it had been in the original input
stream (in place of the corresponding macro call). Thus, any commas or
right parentheses within the value of a nested call are as effective as
those in the original input text. (Remember however that commas within
nested parentheses are not argument separators.) After argument col‐
lection, 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 rede‐
fined, but once this is done the original meaning is lost. Their val‐
ues are null unless otherwise stated.
changecom
Change the starting and ending delimiters for subsequent com‐
ments to the first and second arguments. If the second argument
is missing or an empty string, comments will be ended by new‐
line. If there are no arguments, there are no comments.
changequote
Change quote characters to the first and second arguments.
Changequote without arguments restores the original values of
`'.
copydef
The second argument is installed with the value of the macro
named by the first argument, which may be a built-in macro.
Typically both arguments are quoted to prevent too early expan‐
sion. A macro can be renamed using copydef followed by unde‐
fine.
define The second argument is installed as the value of the macro named
by the first argument. When the macro is later called
(expanded), each occurrence in the replacement text of $n, where
n is a digit, is replaced by the n-th argument of that macro
call. Argument 0 is the name of the macro; missing arguments
are replaced by the null string. If the macro value is the same
as its name, or the value is $0, the result is the macro name.
To prevent expansion of a name when redefining a macro, quote
the first argument.
divert M4 maintains 10 output streams, numbered 0-9. The final output
is the concatenation of the streams in numerical order; ini‐
tially stream 0 is the current stream. The divert macro changes
the current output stream to its (digit-string) argument. Out‐
put diverted to a stream other than 0 through 9 is discarded.
divnum Returns the value of the current output stream.
dnl Reads and discards characters up to and including the next new‐
line.
dumpdef
Prints current names and definitions, for the named items, or
for all if no arguments are given.
errprint
Prints its argument on the diagnostic output file.
eval Evaluates its argument as an arithmetic expression, using 32-bit
arithmetic, and returns the result as a signed decimal integer.
The only literals are decimal integers. Operators are those of
Limbo: the binary operators ||, &&, |, ^, &, == !=, < > >= <=,
<< >> (arithmetic shifts), + -, * / %, ** (power); the unary
operators +, -, ~, !; and parenthesis. Operator precedence is
the same as in Limbo. Right shifts are signed.
ifdef If the first argument is defined, the value is the second argu‐
ment, otherwise the third. If there is no third argument, the
value is null. The word inferno is predefined with `inferno' as
its replacement text.
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, the process is repeated with arguments 4, 5, 6 and so on,
in groups of three. If no match is found, the result is the
remaining argument (not part of a group of three), or null if
none is present.
include
Returns the contents of the file named in the argument.
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.
index Returns the position in its first argument where the second
argument begins (zero origin), or -1 if the second argument does
not occur.
len Returns the number of characters in its argument.
maketemp
Returns its first argument after replacing any trailing XXXs by
the current host name, process ID, and a unique letter. Nor‐
mally used to create unique temporary file names.
sinclude
The same as include, except that it says nothing if the file is
inaccessible.
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.
syscmd Runs the first argument as an sh(1) command. No value is
returned. Note that the output of a command can be redirected
to a temporary file named by maketemp, included, and then
removed.
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.
undefine
Removes the definition of the macro named in its argument.
undivert
Causes immediate output of text from diversions named as argu‐
ments, or all diversions if no argument. Text may be undiverted
into another diversion. Undiverting discards the diverted text.
M4 interprets its command line options after installing the predefined
macro set. The -D option defines name as a macro with the given value;
-Q defines name as a macro with the given value that is regarded as
always quoted (ie, is never rescanned). Neither -D nor -Q may change a
predefined macro. The -U option undefines the given macro name, which
may be one of the predefined macros.
M4 in Inferno is more closely related to the original m4 in Seventh
Edition UNIX than its more elaborate relatives in System V and POSIX.
SEE ALSO
B. W. Kernighan and D. M. Ritchie, The M4 Macro Processor
M4(1)