m4(1posix)
NAME
m4 --- macro processor
SYNOPSIS
m4 [s] [D name[=val]]... [U name]... file...
DESCRIPTION
The m4 utility is a macro processor that shall read one or more text files, process them according to their included macro statements, and write the results to standard output.
OPTIONS
The m4 utility shall conform to the Base Definitions volume of
POSIX.12008, Section 12.2, Utility Syntax Guidelines, except that the
order of the D and U options shall be significant, and options can be
interspersed with operands.
The following options shall be supported:
s Enable line synchronization output for the c99 preprocessor
phase (that is, #line directives).
D name[=val]
Define name to val or to null if =val is omitted.
U name Undefine name.
OPERANDS
The following operand shall be supported:
file A pathname of a text file to be processed. If no file is
given, or if it is '', the standard input shall be read.
STDIN
The standard input shall be a text file that is used if no file operand is given, or if it is ''.
INPUT FILES
The input file named by the file operand shall be a text file.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of m4:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.12008, Section 8.2, Internationalization
Variables for the precedence of internationalization
variables used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input
files).
LC_MESSAGES
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard
error.
NLSPATH Determine the location of message catalogs for the processing
of LC_MESSAGES.
ASYNCHRONOUS EVENTS
Default.
STDOUT
The standard output shall be the same as the input files, after being processed for macro expansion.
STDERR
The standard error shall be used to display strings with the errprint macro, macro tracing enabled by the traceon macro, the defined text for macros written by the dumpdef macro, or for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
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 is the exit code. The default is zero. It shall be an
error to specify an argument containing any non-numeric
characters.
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 first argument shall be taken as a template for creating
an empty file, with trailing 'X' characters replaced with
characters from the portable filename character set. The
behavior is unspecified if the first argument does not end in
at least six 'X' characters. If a temporary file is
successfully created, then the defining text of the macro
shall be the name of the new file. The user ID of the file
shall be set to the effective user ID of the process. The
group ID of the file shall be set to the group ID of the
file's parent directory or to the effective group ID of the
process. The file access permission bits are set such that
only the owner can both read and write the file, regardless
of the current umask of the process. If a file could not be
created, 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.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred
If the m4exit macro is used, the exit value can be specified by the
input file.
CONSEQUENCES OF ERRORS
Default. The following sections are informative.
APPLICATION USAGE
The defn macro is useful for renaming macros, especially built-ins. Since eval defers to the ISO C standard, some operations have undefined behavior. In some implementations, division or remainder by zero cause a fatal signal, even if the division occurs on the short-circuited branch of "&&" or "||". Any operation that overflows in signed arithmetic produces undefined behavior. Likewise, using the shift operators with a shift amount that is not positive and smaller than the precision is undefined, as is shifting a negative number to the right. Historically, not all implementations obeyed C-language precedence rules: '~' and '!' were lower than '=='; '==' and '!=' were not lower than '<'; and '|' was not lower than '^'; the liberal use of "()" can force the desired precedence even with these non-compliant implementations. Furthermore, some traditional implementations treated '^' as an exponentiation operator, although most implementations now use "**" as an extension for this purpose. When a macro has been multiply defined via the pushdef macro, it is unspecified whether the define macro will alter only the most recent definition (as though by popdef and pushdef), or replace the entire stack of definitions with a single definition (as though by undefine and pushdef). An application desiring particular behavior for the define macro in this case can redefine it accordingly. Applications should use the mkstemp macro instead of the obsolescent maketemp macro for creating temporary files.
EXAMPLES
If the file m4src contains the lines:
The value of `VER' is "VER".
ifdef(`VER', ``VER'' is defined to be VER., VER is not defined.)
ifelse(VER, 1, ``VER'' is `VER'.)
ifelse(VER, 2, ``VER'' is `VER'., ``VER'' is not 2.)
end
then the command
m4 m4src
or the command:
m4 U VER m4src
produces the output:
The value of VER is "VER".
VER is not defined.
VER is not 2.
end
The command:
m4 D VER m4src
produces the output:
The value of VER is "".
VER is defined to be .
VER is not 2.
end
The command:
m4 D VER=1 m4src
produces the output:
The value of VER is "1".
VER is defined to be 1.
VER is 1.
VER is not 2.
end
The command:
m4 D VER=2 m4src
produces the output:
The value of VER is "2".
VER is defined to be 2.
VER is 2.
end
RATIONALE
Historic System V-based behavior treated "${" in a macro definition as
two literal characters. However, this sequence is left unspecified so
that implementations may offer extensions such as "${11}" meaning the
eleventh positional parameter. Macros can still be defined with
appropriate uses of nested quoting to result in a literal "${" in the
output after rescanning removes the nested quotes.
In the translit built-in, historic System V-based behavior treated ''
as a literal; GNU behavior treats it as a range. This version of the
standard allows either behavior.
FUTURE DIRECTIONS
None.
SEE ALSO
c99 The Base Definitions volume of POSIX.12008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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