The m4 utility is a macro processor intended as a front end for C, assembler, and other languages. Each of the argument files is processed in order. If there are no files, or if a file is -, the standard input is read. The processed text is written
on the standard output. Note:m4 cannot include more than nine nested files and writes a diagnostic message if that number is exceeded.
Macro Syntax
Macro calls have the form:
name(arg1,arg2, ..., argn)
The open parenthesis character, (, must immediately follow the name of the macro. If the name of a defined macro is not followed by a (, it is deemed to be a call of that macro with no arguments. Potential macro names consist of alphanumeric characters
and underscore (_), where the first character is not a digit.
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.
Macro Processing
When a macro name is recognized, its arguments are collected by searching for a matching right parenthesis. 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 parentheses that happen to turn up within the value of a nested call are as effective as those in the original input text. After argument collection, the value of the macro is pushed back onto the input stream and rescanned.
OPTIONS
The options and their effects are as follows:
-Bint
Changes the size of the push-back and argument collection buffers from the default of 4,096.
-e
Operates interactively. Interrupts are ignored and the output is unbuffered.
-Hint
Changes the size of the symbol table hash array from the default of 199. The size should be prime.
-s
Enables line sync output for the C preprocessor (#line ...)
-Sint
Changes the size of the call stack from the default of 100slots. Macros take three slots, and non-macro arguments take one.
-Tint
Changes the size of the token buffer from the default of 512bytes.
To be effective, the above flags must appear before any file names and before any -D or -U flags:
-Dname[=val]
Defines name to val or to NULL in val's absence.
-Uname
Undefines name.
OPERANDS
The following operand is supported:
file
A path name of a text file to be processed. If no file is given, or if it is -, the standard input is read.
USAGE
The m4 utility makes available the following built-in macros. These macros can be redefined, but once this is done the original meaning is lost. Their values are NULL unless otherwise stated.
changequote
Change quote symbols to the first and second arguments. The symbols can be up to five characters long. changequote without arguments restores the original values (that is, `').
changecom
Change left and right comment markers from the default # and NEWLINE. With no arguments, the comment mechanism is effectively disabled. With one argument, the left marker becomes the argument and the right marker becomes NEWLINE.
With two arguments, both markers are affected. Comment markers can be up to five characters long.
decr
Returns the value of its argument decremented by 1.
define
The second argument is installed as the value of the macro whose name is the first argument. 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; $# is replaced by the number of arguments; $* is replaced by a list of all the arguments separated by commas; $@ is like $*,
but each argument is quoted (with the current quotes).
defn
Returns the quoted definition of its argument(s). It is useful for renaming macros, especially built-ins.
divert
m4 maintains 10 output streams, numbered 0-9. The final output is the concatenation of the streams in numerical order. 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 discarded.
divnum
Returns the value of the current output stream.
dnl
Reads and discards characters up to and including the next NEWLINE.
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.
ifdef
If the first argument is defined, the value is the second argument, otherwise the third. If there is no third argument, the value is NULL. The word unix is predefined.
ifelse
This macro 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, and if there are more than four arguments, the process is repeated with arguments 4, 5, 6 and 7. Otherwise, the value is either the fourth
string, or, if it is not present, NULL.
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.
m4exit
This macro causes immediate exit from m4. Argument 1, if given, is the exit code; the default is 0.
m4wrap
Argument 1 is pushed back at final EOF. Example: m4wrap(`cleanup()')
maketemp
Fills in a string of "X" characters in its argument with the current process ID.
popdef
Removes current definition of its argument(s), exposing the previous one, if any.
pushdef
Like define, but saves any previous definition.
shift
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 is subsequently be performed.
sinclude
This macro is identical to 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
This macro executes the command given in the first argument. No value is returned.
sysval
This macro is the return code from the last call to syscmd.
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.
traceon
This macro with no arguments, turns on tracing for all macros (including built-ins). Otherwise, turns on tracing for named macros.
traceoff
Turns off trace globally and for any macros specified.
undefine
Removes the definition of the macro named in its argument.
undivert
This macro causes immediate output of text from diversions named as arguments, or all diversions if no argument. Text can be undiverted into another diversion. Undiverting discards the diverted text.
/usr/bin/m4
eval
Evaluates its argument as an arithmetic expression, using 32-bit signed-integer arithmetic. The following operators are supported: parentheses, unary -, unary +, !, ~, *, /, %, +, -, relationals, bitwise &, |, &&, and ||. Octal and hex numbers can be specified as in
C. The second argument specifies the radix for the result; the default is 10. The third argument can be used to specify the minimum number of digits in the result.
/usr/xpg4/bin/m4
eval
Evaluates its argument as an arithmetic expression, using 32-bit signed-integer arithmetic. The following operators are supported: parentheses, unary -, unary +, !, ~, *, /, %, +, -, <<, >>, relationals, bitwise &, |, &&, and ||. Precedence and associativity
are as in C. Octal and hex numbers can also be specified as in C. The second argument specifies the radix for the result; the default is 10. The third argument can be used to specify the minimum number of digits in the result.
EXAMPLES
Example 1 Examples of m4 files
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
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of m4: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.
EXIT STATUS
The following exit values are returned:
0
Successful completion.
>0
An error occurred
If the m4exit macro is used, the exit value can be specified by the input file.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
