The m4 utility shall compare each token from the input against
the set of built-in and user-defined macros. If the token matches
the name of a macro, then the token shall be replaced by the
macro's defining text, if any, and rescanned for matching macro
names. Once no portion of the token matches the name of a macro,
it shall be written to standard output. Macros may have
arguments, in which case the arguments shall be substituted into
the defining text before it is rescanned.
Macro calls have the form:
name(arg1, arg2, ..., argn)
Macro names shall consist of letters, digits, and underscores,
where the first character is not a digit. Tokens not of this form
shall not be treated as macros.
The application shall ensure that the <left-parenthesis>
immediately follows the name of the macro. If a token matching
the name of a macro is not followed by a <left-parenthesis>, it
is handled as a use of that macro without arguments.
If a macro name is followed by a <left-parenthesis>, its
arguments are the <comma>-separated tokens between the <left-
parenthesis> and the matching <right-parenthesis>. Unquoted
white-space characters preceding each argument shall be ignored.
All other characters, including trailing white-space characters,
are retained. <comma> characters enclosed between <left-
parenthesis> and <right-parenthesis> characters do not delimit
arguments.
Arguments are positionally defined and referenced. The string
"$1" in the defining text shall be replaced by the first
argument. Systems shall support at least nine arguments; only the
first nine can be referenced, using the strings "$1" to "$9",
inclusive. The string "$0" is replaced with the name of the
macro. The string "$#" is replaced by the number of arguments as
a string. The string "$*" is replaced by a list of all of the
arguments, separated by <comma> characters. The string "$@" is
replaced by a list of all of the arguments separated by <comma>
characters, and each argument is quoted using the current left
and right quoting strings. The string "${" produces unspecified
behavior.
If fewer arguments are supplied than are in the macro definition,
the omitted arguments are taken to be null. It is not an error if
more arguments are supplied than are in the macro definition.
No special meaning is given to any characters enclosed between
matching left and right quoting strings, but the quoting strings
are themselves discarded. By default, the left quoting string
consists of a grave accent (backquote) and the right quoting
string consists of an acute accent (single-quote); see also the
changequote macro.
Comments are written but not scanned for matching macro names; by
default, the begin-comment string consists of the <number-sign>
character and the end-comment string consists of a <newline>.
See also the changecom and dnl macros.
The m4 utility shall make available the following built-in
macros. They can be redefined, but once this is done the original
meaning is lost. Their values shall be null unless otherwise
stated. In the descriptions below, the term defining text refers
to the value of the macro: the second argument to the define
macro, among other things. Except for the first argument to the
eval macro, all numeric arguments to built-in macros shall be
interpreted as decimal values. The string values produced as the
defining text of the decr, divnum, incr, index, len, and sysval
built-in macros shall be in the form of a decimal-constant as
defined in the C language.
changecom The changecom macro shall set the begin-comment and
end-comment strings. With no arguments, the comment
mechanism shall be disabled. With a single non-null
argument, that argument shall become the begin-comment
and the <newline> shall become the end-comment string.
With two non-null arguments, the first argument shall
become the begin-comment string and the second argument
shall become the end-comment string. The behavior is
unspecified if either argument is provided but null.
Systems shall support comment strings of at least five
characters.
changequote
The changequote macro shall set the begin-quote and
end-quote strings. With no arguments, the quote strings
shall be set to the default values (that is, `'). The
behavior is unspecified if there is a single argument
or either argument is null. With two non-null
arguments, the first argument shall become the begin-
quote string and the second argument shall become the
end-quote string. Systems shall support quote strings
of at least five characters.
decr The defining text of the decr macro shall be its first
argument decremented by 1. It shall be an error to
specify an argument containing any non-numeric
characters. The behavior is unspecified if decr is not
immediately followed by a <left-parenthesis>.
define The second argument shall become the defining text of
the macro whose name is the first argument. It is
unspecified whether the define macro deletes all prior
definitions of the macro named by its first argument or
preserves all but the current definition of the macro.
The behavior is unspecified if define is not
immediately followed by a <left-parenthesis>.
defn The defining text of the defn macro shall be the quoted
definition (using the current quoting strings) of its
arguments. The behavior is unspecified if defn is not
immediately followed by a <left-parenthesis>.
divert The m4 utility maintains nine temporary buffers,
numbered 1 to 9, inclusive. When the last of the input
has been processed, any output that has been placed in
these buffers shall be written to standard output in
buffer-numerical order. The divert macro shall divert
future output to the buffer specified by its argument.
Specifying no argument or an argument of 0 shall resume
the normal output process. Output diverted to a stream
with a negative number shall be discarded. Behavior is
implementation-defined if a stream number larger than 9
is specified. It shall be an error to specify an
argument containing any non-numeric characters.
divnum The defining text of the divnum macro shall be the
number of the current output stream as a string.
dnl The dnl macro shall cause m4 to discard all input
characters up to and including the next <newline>.
dumpdef The dumpdef macro shall write the defined text to
standard error for each of the macros specified as
arguments, or, if no arguments are specified, for all
macros.
errprint The errprint macro shall write its arguments to
standard error. The behavior is unspecified if errprint
is not immediately followed by a <left-parenthesis>.
eval The eval macro shall evaluate its first argument as an
arithmetic expression, using signed integer arithmetic
with at least 32-bit precision. At least the following
C-language operators shall be supported, with
precedence, associativity, and behavior as described in
Section 1.1.2.1, Arithmetic Precision and Operations:
()
unary +
unary -
~
!
binary *
/
%
binary +
binary -
<<
>>
<
<=
>
>=
==
!=
binary &
^
|
&&
||
Systems shall support octal and hexadecimal numbers as
in the ISO C standard. The second argument, if
specified, shall set the radix for the result; if the
argument is blank or unspecified, the default is 10.
Behavior is unspecified if the radix falls outside the
range 2 to 36, inclusive. The third argument, if
specified, sets the minimum number of digits in the
result. Behavior is unspecified if the third argument
is less than zero. It shall be an error to specify the
second or third argument containing any non-numeric
characters. The behavior is unspecified if eval is not
immediately followed by a <left-parenthesis>.
ifdef If the first argument to the ifdef macro is defined,
the defining text shall be the second argument.
Otherwise, the defining text shall be the third
argument, if specified, or the null string, if not. The
behavior is unspecified if ifdef is not immediately
followed by a <left-parenthesis>.
ifelse The ifelse macro takes three or more arguments. If the
first two arguments compare as equal strings (after
macro expansion of both arguments), the defining text
shall be the third argument. If the first two arguments
do not compare as equal strings and there are three
arguments, the defining text shall be null. If the
first two arguments do not compare as equal strings and
there are four or five arguments, the defining text
shall be the fourth argument. If the first two
arguments do not compare as equal strings and there are
six or more arguments, the first three arguments shall
be discarded and processing shall restart with the
remaining arguments. The behavior is unspecified if
ifelse is not immediately followed by a <left-
parenthesis>.
include The defining text for the include macro shall be the
contents of the file named by the first argument. It
shall be an error if the file cannot be read. The
behavior is unspecified if include is not immediately
followed by a <left-parenthesis>.
incr The defining text of the incr macro shall be its first
argument incremented by 1. It shall be an error to
specify an argument containing any non-numeric
characters. The behavior is unspecified if incr is not
immediately followed by a <left-parenthesis>.
index The defining text of the index macro shall be the first
character position (as a string) in the first argument
where a string matching the second argument begins
(zero origin), or -1 if the second argument does not
occur. The behavior is unspecified if index is not
immediately followed by a <left-parenthesis>.
len The defining text of the len macro shall be the length
(as a string) of the first argument. The behavior is
unspecified if len is not immediately followed by a
<left-parenthesis>.
m4exit Exit from the m4 utility. If the first argument is
specified, it shall be the exit code. If no argument is
specified, the exit code shall be zero. It shall be an
error to specify an argument containing any non-numeric
characters. If the first argument is zero or no
argument is specified, and an error has previously
occurred (for example, a file operand that could not be
opened), it is unspecified whether the exit status is
zero or non-zero.
m4wrap The first argument shall be processed when EOF is
reached. If the m4wrap macro is used multiple times,
the arguments specified shall be processed in the order
in which the m4wrap macros were processed. The behavior
is unspecified if m4wrap is not immediately followed by
a <left-parenthesis>.
maketemp The defining text shall be the first argument, with any
trailing 'X' characters replaced with the current
process ID as a string. The behavior is unspecified if
maketemp is not immediately followed by a <left-
parenthesis>.
mkstemp The defining text shall be as if it were the resulting
pathname after a successful call to the mkstemp()
function defined in the System Interfaces volume of
POSIX.1‐2017 called with the first argument to the
macro invocation. If a file is created, that file shall
be closed. If a file could not be created, the m4
utility shall write a diagnostic message to standard
error and shall continue processing input but its final
exit status shall be non-zero; the defining text of the
macro shall be the empty string. The behavior is
unspecified if mkstemp is not immediately followed by a
<left-parenthesis>.
popdef The popdef macro shall delete the current definition of
its arguments, replacing that definition with the
previous one. If there is no previous definition, the
macro is undefined. The behavior is unspecified if
popdef is not immediately followed by a <left-
parenthesis>.
pushdef The pushdef macro shall be equivalent to the define
macro with the exception that it shall preserve any
current definition for future retrieval using the
popdef macro. The behavior is unspecified if pushdef is
not immediately followed by a <left-parenthesis>.
shift The defining text for the shift macro shall be a comma-
separated list of its arguments except the first one.
Each argument shall be quoted using the current quoting
strings. The behavior is unspecified if shift is not
immediately followed by a <left-parenthesis>.
sinclude The sinclude macro shall be equivalent to the include
macro, except that it shall not be an error if the file
is inaccessible. The behavior is unspecified if
sinclude is not immediately followed by a <left-
parenthesis>.
substr The defining text for the substr macro shall be the
substring of the first argument beginning at the zero-
offset character position specified by the second
argument. The third argument, if specified, shall be
the number of characters to select; if not specified,
the characters from the starting point to the end of
the first argument shall become the defining text. It
shall not be an error to specify a starting point
beyond the end of the first argument and the defining
text shall be null. It shall be an error to specify an
argument containing any non-numeric characters. The
behavior is unspecified if substr is not immediately
followed by a <left-parenthesis>.
syscmd The syscmd macro shall interpret its first argument as
a shell command line. The defining text shall be the
string result of that command. The string result shall
not be rescanned for macros while setting the defining
text. No output redirection shall be performed by the
m4 utility. The exit status value from the command can
be retrieved using the sysval macro. The behavior is
unspecified if syscmd is not immediately followed by a
<left-parenthesis>.
sysval The defining text of the sysval macro shall be the exit
value of the utility last invoked by the syscmd macro
(as a string).
traceon The traceon macro shall enable tracing for the macros
specified as arguments, or, if no arguments are
specified, for all macros. The trace output shall be
written to standard error in an unspecified format.
traceoff The traceoff macro shall disable tracing for the macros
specified as arguments, or, if no arguments are
specified, for all macros.
translit The defining text of the translit macro shall be the
first argument with every character that occurs in the
second argument replaced with the corresponding
character from the third argument. If no replacement
character is specified for some source character
because the second argument is longer than the third
argument, that character shall be deleted from the
first argument in translit's defining text. The
behavior is unspecified if the '-' character appears
within the second or third argument anywhere besides
the first or last character. The behavior is
unspecified if the same character appears more than
once in the second argument. The behavior is
unspecified if translit is not immediately followed by
a <left-parenthesis>.
undefine The undefine macro shall delete all definitions
(including those preserved using the pushdef macro) of
the macros named by its arguments. The behavior is
unspecified if undefine is not immediately followed by
a <left-parenthesis>.
undivert The undivert macro shall cause immediate output of any
text in temporary buffers named as arguments, or all
temporary buffers if no arguments are specified.
Buffers can be undiverted into other temporary buffers.
Undiverting shall discard the contents of the temporary
buffer. The behavior is unspecified if an argument
contains any non-numeric characters.
