NAME
m4 - macro processor (DEVELOPMENT)
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
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines, except
that the order of the -D and -U options shall be significant.
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
IEEE Std 1003.1-2001, 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 <blank>s and <newline>s preceding
each argument shall be ignored. All other characters, including
trailing <blank>s and <newline>s, are retained. Commas enclosed
between left 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 "$*" is replaced by a
list of all of the arguments, separated by commas. The string "$@" is
replaced by a list of all of the arguments separated by commas, and
each argument is quoted using the current left and right quoting
strings.
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 ( ’‘’ ) and the right quoting string consists of an acute accent
( ’" ); 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 argument, that argument shall become the
begin-comment string and the <newline> shall become the end-
comment string. With two arguments, the first argument shall
become the begin-comment string and the second argument shall
become the end-comment string. 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, ‘’). With a single argument, that
argument shall become the begin-quote string and the <newline>
shall become the end-quote string. With two 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.
define The second argument shall become the defining text of the macro
whose name is the first argument.
defn The defining text of the defn macro shall be the quoted
definition (using the current quoting strings) of its arguments.
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
other than 0 to 9 shall be discarded. 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.
eval The eval macro shall evaluate its first argument as an
arithmetic expression, using 32-bit signed integer arithmetic.
All of the C-language operators shall be supported, except for:
[]
->
++
--
(type)
unary *
sizeof,
.
?:
unary &
and all assignment operators. It shall be an error to specify any of
these operators. Precedence and associativity shall be as in the ISO C
standard. 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; the default is 10. The third argument, if specified,
sets the minimum number of digits in the result. It shall be an error
to specify the second or third argument containing any non-numeric
characters.
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.
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.
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.
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.
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.
len The defining text of the len macro shall be the length (as a
string) of the first argument.
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.
maketemp
The defining text shall be the first argument, with any trailing
’X’ characters replaced with the current process ID as a string.
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.
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.
shift The defining text for the shift macro shall be all of its
arguments except for the first one.
sinclude
The sinclude macro shall be equivalent to the include macro,
except that it shall not be an error if the file is
inaccessible.
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.
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. No output redirection shall be performed by the m4
utility. The exit status value from the command can be retrieved
using the sysval macro.
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.
undefine
The undefine macro shall delete all definitions (including those
preserved using the pushdef macro) of the macros named by its
arguments.
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. It shall be an error to specify an
argument containing 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.
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
None.
FUTURE DIRECTIONS
None.
SEE ALSO
c99
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .