m4(C)

m4 -- macro processor

Syntax

m4 [ options ] [ file ] ...

Description

The m4(C) command is a macro processor for use as a front-end for C and assembly languages, as well as other languages. Each input file is processed in order; if no file names are specified, or if the file is ``-'', standard input is read. The processed text is written to standard output. It is used primarily as part of a development environment, but can also be useful in creating input files to other programs whose input format follows a specific grammar.

The options and their effects are as follows:

-e: Operate interactively. Interrupts are ignored and the output is unbuffered.
-s: Enable line-sync output for the C preprocessor (#line ...)
-Bint: Change the size of the push-back and argument collection buffers from the default of 4,096.
-Hint: Change the size of the symbol table hash array from the default of 199. The size should be prime.
-Sint: Change the call stack size from the default of 100 slots. Macros take three slots, and non-macro arguments take one.
-Tint: Change the token buffer size from the default of 512 bytes.
-V: Print release and version information.

To be effective, these 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.

Macro calls have the form:

name(arg1,arg2, ..., argn)

The open parenthesis, ``('', must immediately follow the macro name. If the name of a defined macro is not followed by a close parenthesis, ``)'', it is deemed to be a call of that macro with no arguments. Potential macro names consist of alphabetic letters, digits, and underscore ``_'', where the first character is not a digit.

Leading unquoted blanks, tabs, and new-lines 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 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 which 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.

m4 makes the following built-in macros available. They can be redefined, but once this is done, the original meaning is lost. Their values are null unless otherwise stated.

define: Takes two arguments: the first is the macro name, and the second is its definition. When the macro name appears in the input text, it will be replaced by its definition. The macro definition can be a simple text string or can involve arguments. Arguments are of the form $n, where n is a digit between 0 and 9. If an occurrence of a macro name is followed by a comma-separated list of values, enclosed in parentheses, then when the macro substitution takes place, the nth value in the list replaces the $n. $0 is the name of the macro; missing arguments are replaced by a 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). The replacement text is then reprocessed by m4.
undefine: Removes the definition of the macro named in its argument.
defn: Returns the quoted definition of its argument(s). It is useful for renaming macros, especially built-ins.
pushdef: Operates like define, but saves any previous definition.
popdef: Removes current definition of its argument(s), exposing the previous one, if any.
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 on some versions of m4.
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 will subsequently be performed.
changequote: Changes quote symbols to the first and second arguments. The symbols can be up to five characters long. changequote without arguments (`´)restores the original values.
changecom: Changes left and right comment markers from the default # and new-line. With no arguments, the comment mechanism is effectively disabled. With one argument, the left marker becomes the argument and the right marker becomes a new-line. With two arguments, both markers are affected. Comment markers can be up to five characters long.
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. divert changes the current output stream to its (digit-string) argument. Output diverted to a stream other than 0 through 9 is discarded.
undivert: Causes immediate output of text from diversions named as arguments, or all diversions if no argument is supplied. Text can be ``undiverted'' into another diversion.
divnum: Returns the value of the current output stream.
dnl: Reads and discards characters up to and including the next new-line.
ifelse: 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.
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.
decr: Returns the value of its argument decremented by 1.
eval: Evaluates its argument as an arithmetic expression, using 32-bit arithmetic. Operators include +, -, , /, %, ^ (exponentiation), bitwise &, |, ^, and ~; relationals; parentheses. 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.
len: Returns the number of characters in its argument.
index: Returns the position in its first argument where the second argument begins (zero origin), or -1 if the second argument does not occur.
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.
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.
include: Returns the contents of the file named in the argument.
sinclude: Is identical to include, except that it says nothing if the file is inaccessible.
syscmd: Executes the system command given in the first argument. No value is returned.
sysval: The return code from the last call to syscmd.
maketemp: Fills in a string of XXXXX in its argument with the current process ID.
m4exit: Causes immediate exit from m4. Argument 1, if given, is the exit code; the default is 0.
m4wrap: Pushes back argument 1 at final EOF; for example:

m4wrap(`cleanup()´)
errprint: Prints its argument on the diagnostic output file.
dumpdef: Prints current names and definitions for the named items or for all if no arguments are given.
traceon: 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. Macros specifically traced by traceon can be untraced only by specific calls to traceoff.

Exit values

The m4 command returns an exit value of 0 if no error occurred, otherwise it returns a non-zero value.

Files

: /usr/bin/m4

Standards conformance

m4 is conformant with: