M4 is a macro processor intended as a front end for Ratfor, Pas-
cal, and other languages that do not have a built-in macro pro-
cessing capability. M4 reads standard input, the processed text
is written on the standard output. The options and their effects
are as follows:
-D name[=val]Defines name to val, or to null in val's ab-
sence.
-U name 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 taken to be a
call of that macro with no arguments, i.e. name(). Potential
macro names consist of alphabetic letters and digits. Leading
unquoted blanks, tabs and newlines 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 ). 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 paren-
theses which happen to turn up within the value of a nested call
are as effective as those in the original input text. (This is
typically referred as inside-out macro expansion.) After argu-
ment 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 oth-
erwise stated. define "(name [, val])" the second argument is
installed as the value of the macro whose name is the first argu-
ment. If there is no second argument, the value is null. 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. defn
"(name [, name ...])" returns the quoted definition of its argu-
ment(s). Useful in renaming macros. undefine ";(name [, name
...])" removes the definition of the macro(s) named. If there is
more than one definition for the named macro, (due to previous
use of pushdef) all definitions are removed. pushdef "(name [,
val])" like define, but saves any previous definition by stacking
the current definition. popdef ";(name [, name ...])" removes
current definition of its argument(s), exposing the previous one
if any. ifdef ";(name, if-def [, ifnot-def])" if the first argu-
ment is defined, the value is the second argument, otherwise the
third. If there is no third argument, the value is null. A word
indicating the current operating system is predefined. (e.g.
unix or vms). shift ";(arg, arg, arg, ...)" 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
"(lqchar, rqchar)" change quote symbols to the first and second
arguments. With no arguments, the quotes are reset back to the
default characters. (i.e., `'). changecom "(lcchar, rcchar)"
change left and right comment markers from the default # and new-
line. With no arguments, the comment mechanism is reset back to
the default characters. With one argument, the left marker be-
comes the argument and the right marker becomes newline. With
two arguments, both markers are affected. divert ";(divnum)"
maintains 10 output streams, numbered 0-9. 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 lost. undivert "([divnum [, di-
vnum ...]])" causes immediate output of text from diversions
named as argument(s), or all diversions if no argument. Text may
be undiverted into another diversion. Undiverting discards the
diverted text. At the end of input processing, M4 forces an au-
tomatic undivert unless is defined. divnum ";()" returns the val-
ue of the current output stream. dnl ";()" reads and discards
characters up to and including the next newline. ifelse "(arg,
arg, if-same [, ifnot-same | arg, arg ...])" has three or more
arguments. If the first argument is the same string as the sec-
ond, then the value is the third argument. If not, and if there
are more than four arguments, the process is repeated with argu-
ments 4, 5, 6 and 7. Otherwise, the value is either the fourth
string, or, if it is not present, null. incr ";(num)" returns the
value of its argument incremented by 1. The value of the argu-
ment is calculated by interpreting an initial digit-string as a
decimal number. decr ";(num)" returns the value of its argument
decremented by 1. eval ";(expression)" evaluates its argument as
a constant expression, using integer arithmetic. The evaluation
mechanism is very similar to that of cpp (#if expression). The
expression can involve only integer constants and character con-
stants, possibly connected by the binary operators
* / % + - >> << < > <= >= ==
!= & ^ | && ||
or the unary operators - ! or tilde or by the ternary operator ?
: . Parentheses may be used for grouping. Octal numbers may be
specified as in C. len ";(string)" returns the number of charac-
ters in its argument. index ";(search-string, string)" returns
the position in its first argument where the second argument be-
gins (zero origin), or 1 if the second argument does not occur.
substr ";(string, index [, length])" returns a substring of its
first argument. The second argument is a zero origin number se-
lecting the first character (internally treated as an expres-
sion); 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 "(source, from [, to])"
transliterates the characters in its first argument from the set
given by the second argument to the set given by the third. If
the third argument is shorter than the second, all extra charac-
ters in the second argument are deleted from the first argument.
If the third argument is missing altogether, all characters in
the second argument are deleted from the first argument. include
"(filename)" returns the contents of the file that is named in
the argument. sinclude "(filename)"is identical to include, ex-
cept that it says nothing if the file is inaccessable. paste
"(filename)" returns the contents of the file named in the argu-
ment without any processing, unlike include. spaste ";(filename)"
is identical to paste, except that it says nothing if the file is
inaccessibl[De. syscmd "(command)" executes the command given in
the first argument. No value is returned. sysval "()" is the
return code from the last call to syscmd.
.PP maketemp (string)" fills in a string of XXXXXX in its argu-
ment with the current process ID. m4exit ";([exitcode])" causes
immediate exit from M4. Argument 1, if given, is the exit code;
the default is 0. m4wrap ";(m4-macro-or-built-n)" argument 1 will
be pushed back at final EOF; example: m4wrap(`dumptable()'). er-
rprint "(str [, str, str, ...])" prints its argument(s) on
stderr. If there is more than one argument, each argument is sep-
arated by a space during the output. An arbitrary number of ar-
guments may be supplied. dumpdef ";([name, name, ...])" prints
current names and definitions, for the named items, or for all if
no arguments are given. M4 was written by Ozan S. Yigif.