||FreeBSD General Commands Manual
macro language processor
utility is a macro processor that can
be used as a front end to any language (e.g., C, ratfor, fortran, lex, and
yacc). If no input files are given,
reads from the standard input, otherwise files specified on the command line
are processed in the given order. Input files can be regular files, files in
the m4 include paths, or a single dash (‘-’), denoting standard
writes the processed text to the
standard output, unless told otherwise.
Macro calls have the form name(argument1[, argument2, ..., argumentN]).
There cannot be any space following the macro name and the open parenthesis
(‘(’). If the macro name is not followed by an open parenthesis
it is processed with no arguments.
Macro names consist of a leading alphabetic or underscore possibly followed by
alphanumeric or underscore characters, e.g., valid macro names match the
In arguments to macros, leading unquoted space, tab, and newline
(‘\n’) characters are ignored. To quote strings, use left and
right single quotes (e.g., ‘ this is a string with a leading
space’). You can change the quote characters with the
Most built-ins do not make any sense without arguments, and hence are not
recognized as special when not followed by an open parenthesis.
The options are as follows:
- Define the symbol name to have some value
- Set trace flags. flags may hold the
By default, trace is set to “eq”.
- print macro arguments.
- print macro expansion over several lines.
- print result of macro expansion.
- print filename location.
- print line number.
- quote arguments and expansion with the current quotes.
- start with all macros traced.
- number macro expansions.
- turn on all options.
- Activate GNU-m4 compatibility mode. In this mode, translit handles simple
character ranges (e.g., a-z), regular expressions mimic emacs behavior,
multiple m4wrap calls are handled as a stack, the number of diversions is
unlimited, empty names for macro definitions are allowed, and eval
understands ‘0rbase:value’ numbers.
- Add directory dirname to the include
- Send trace output to filename.
- Prefix all built-in macros with ‘m4_’. For example, instead
- Output line synchronization directives, suitable for
- Turn tracing on for macro.
- Undefine the symbol name.
provides the following built-in macros.
They may be redefined, losing their original meaning. Return values are null
unless otherwise stated.
- Calls a built-in by its name, overriding
- Changes the start comment and end comment sequences. Comment sequences may
be up to five characters long. The default values are the hash sign and
the newline character.
With no arguments, comments are turned off. With one single argument, the
end comment sequence is set to the newline character.
- Defines the open quote and close quote sequences. Quote sequences may be
up to five characters long. The default values are the backquote character
and the quote character.
With no arguments, the default quotes are restored. With one single
argument, the close quote sequence is set to the newline character.
`Here is a quoted string'
- Decrements the argument arg by 1. The
argument arg must be a valid numeric
- Define a new macro named by the first argument
name to have the value of the second
argument value. Each occurrence of
‘$n’ (where n is 0 through
9) is replaced by the n'th argument.
‘$0’ is the name of the calling macro. Undefined arguments
are replaced by a null string. ‘$#’ is replaced by the
number of arguments; ‘$*’ is replaced by all arguments comma
separated; ‘$@’ is the same as ‘$*’ but all
arguments are quoted against further expansion.
- Returns the quoted definition for each argument. This can be used to
rename macro definitions (even for built-in macros).
- There are 10 output queues (numbered 0-9). At the end of processing
m4 concatenates all the queues in
numerical order to produce the final output. Initially the output queue is
0. The divert macro allows you to select a new output queue (an invalid
argument passed to divert causes output to be discarded).
- Returns the current output queue number.
- Discard input characters up to and including the next newline.
- Prints the names and definitions for the named items, or for everything if
no arguments are passed.
- Prints the first argument on the standard error output stream.
- Passes its first argument to a shell and returns the shell's standard
output. Note that the shell shares its standard input and standard error
- Computes the first argument as an arithmetic expression using 32-bit
arithmetic. Operators are the standard C ternary, arithmetic, logical,
shift, relational, bitwise, and parentheses operators. You can specify
octal, decimal, and hexadecimal numbers as in C. The optional second
argument radix specifies the radix for
the result and the optional third argument
minimum specifies the minimum number of
digits in the result.
- This is an alias for
- Returns formatstring with escape
sequences substituted with arg1 and
following arguments, in a way similar to
This built-in is only available in GNU-m4 compatibility mode, and the only
parameters implemented are there for autoconf compatibility: left-padding
flag, an optional field width, a maximum field width, *-specified field
widths, and the %s and %c data type.
- If the macro named by the first argument is defined then return the second
argument, otherwise the third. If there is no third argument, the value is
NULL. The word “unix” is
- If the first argument a matches the
second argument b then
ifelse() returns the third argument
yes. If the match fails the three
arguments are discarded and the next three arguments are used until there
is zero or one arguments left, either this last argument or
NULL is returned if no other matches
- Returns the contents of the file specified in the first argument. If the
file is not found as is, look through the include path: first the
directories specified with
-I on the
command line, then the environment variable
M4PATH, as a colon-separated list of
directories. Include aborts with an error message if the file cannot be
- Increments the argument by 1. The argument must be a valid numeric
- Returns the index of the second argument in the first argument (e.g.,
index(the quick brown fox jumped, fox)
returns 16). If the second argument is not found index returns -1.
- Indirectly calls the macro whose name is passed as the first argument,
with the remaining arguments passed as first, ... arguments.
- Returns the number of characters in the first argument. Extra arguments
- Immediately exits with the return value specified by the first argument, 0
- Allows you to define what happens at the final
EOF, usually for cleanup purposes
causes the macro cleanup to be invoked after all other processing is
Multiple calls to
m4wrap() get inserted
in sequence at the final
on the first argument, and returns the modified string. This can be used
to create unique temporary file names.
- Includes the contents of the file specified by the first argument without
any macro processing. Aborts with an error message if the file cannot be
- Substitutes a regular expression in a string with a replacement string.
Usual substitution patterns apply: an ampersand (‘&’) is
replaced by the string matching the regular expression. The string
‘\#’, where ‘#’ is a digit, is replaced by the
- Restores the
pushdefed definition for
- Takes the same arguments as
it saves the definition on a stack for later retrieval by
- Finds a regular expression in a string. If no further arguments are given,
it returns the first match position or -1 if no match. If a third argument
is provided, it returns the replacement string, with sub-patterns
- Returns all but the first argument, the remaining arguments are quoted and
pushed back with commas in between. The quoting nullifies the effect of
the extra scan that will subsequently be performed.
- Similar to
include, except it ignores
- Similar to
paste(), except it ignores
- Returns a substring of the first argument starting at the offset specified
by the second argument and the length specified by the third argument. If
no third argument is present it returns the rest of the string.
- Passes the first argument to the shell. Nothing is returned.
- Returns the return value from the last
- Enables tracing of macro expansions for the given arguments, or for all
macros if no argument is given.
- Disables tracing of macro expansions for the given arguments, or for all
macros if no argument is given.
- Transliterate the characters in the first argument from the set given by
the second argument to the set given by the third. You cannot use
- Removes the definition for the macros specified by its arguments.
- Flushes the named output queues (or all queues if no arguments).
- A pre-defined macro for testing the OS platform.
- Returns the current file's line number.
- Returns the current file's name.
utility exits 0 on success,
and >0 if an error occurs.
But note that the
macro can modify the
utility is compliant with the
IEEE Std 1003.1-2008
The flags [
are extensions to that
is not supposed to be a synonym for
, but instead to be an insecure
temporary file name creation function. It is marked by
IEEE Std 1003.1-2008
as being obsolescent and should not be used
if portability is a concern.
The output format of
are not specified in any standard,
are likely to change and should not be relied upon. The current format of
tracing is closely modelled on
handle macro definitions as a stack.
interacts with the stack in
an undefined way. In this implementation,
replaces the top-most definition
only. Other implementations may erase all definitions on the stack instead.
All built-ins do expand without arguments in many other
have dire size limitations with
respect to buffer sizes.
and Richard A. O'Keefe
GNU-m4 compatibility extensions by Marc Espie
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