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M4(1) General Commands Manual M4(1)
NAME
m4 - macro language processor
SYNOPSIS
m4 [-EGgiPQsv] [-Dname[=value]] [-d flags] [-F filename] [-I dirname]
[-L number] [-o filename] [-R filename] [-t macro] [-Uname] [file ...]
DESCRIPTION
The m4 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, m4 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 input. m4 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, i.e. valid macro names
match the pattern "[a-zA-Z_][a-zA-Z0-9_]*".
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 changequote built-in macro.
Most built-ins don't make any sense without arguments, and hence are not
recognized as special when not followed by an open parenthesis.
The options are as follows:
-D, --define name[=value]
Define the symbol name to have value or to be a null string.
-d, --debug flags
Set trace flags. flags may hold the following:
a print macro arguments.
c print macro expansion over several lines.
e print result of macro expansion.
f print filename location.
l print line number.
q quote arguments and expansion with the current
quotes.
t start with all macros traced.
x number macro expansions.
V turn on all trace flags.
By default, trace is set to `eq'.
-E, --fatal-warnings
Warnings make m4 exit.
-F, --freeze-state filename
Save the input state to filename.
-G, --traditional
Disable GNU m4 extensions.
-g, --gnu 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.
--help Print help message and exit.
-I, --include dirname
Add directory dirname to the include path.
-i, --interactive
Set unbuffered output, disable tty signals.
-L, --nesting-limit
Set the nesting limit in macro expansions. This is
unimplemented and unlimited.
-o, --error-output filename
Send trace output to filename.
-P, --prefix-builtins
Prefix all built-in macros with `m4_'. For example, instead
of writing define, use m4_define.
-Q, --quiet, --silent
Don't print warnings.
-R, --reload-state filename
Reload a previously saved state from filename.
-s, --synclines
Output line synchronization directives, suitable for cpp(1).
-t, --trace macro
Turn tracing on for macro.
-U, --undefine name
Undefine the symbol name.
-v, --version
Print the version and exit.
SYNTAX
m4 provides the following built-in macros. They may be redefined, losing
their original meaning. Return values are null unless otherwise stated.
builtin(name)
Calls a built-in by its name, overriding possible
redefinitions.
changecom(startcomment, endcomment)
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.
# This is a comment
With no arguments, comments are turned off. With one single
argument, the end comment sequence is set to the newline
character.
changequote(beginquote, endquote)
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.
`Here is a quoted string'
With no arguments, the default quotes are restored. With
one single argument, the close quote sequence is set to the
newline character.
decr(arg) Decrements the argument arg by 1. The argument arg must be
a valid numeric string.
define(name, value)
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.
defn(name, ...)
Returns the quoted definition for each argument. This can
be used to rename macro definitions (even for built-in
macros).
divert(num) 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).
divnum Returns the current output queue number.
dnl Discard input characters up to and including the next
newline.
dumpdef(name, ...)
Prints the names and definitions for the named items, or for
everything if no arguments are passed.
errprint(msg)
Prints the first argument on the standard error stream.
esyscmd(cmd)
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 with m4.
eval(expr, radix, minimum)
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.
expr(expr) This is an alias for eval.
format(formatstring, arg1, ...)
Returns formatstring with escape sequences substituted with
arg1 and following arguments, in a way similar to printf(3).
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.
ifdef(name, yes, no)
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
predefined.
ifelse(a, b, yes, ...)
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 were found.
include(name)
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 included.
incr(arg) Increments the argument by 1. The argument must be a valid
numeric string.
index(string, substring)
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.
indir(macro, arg1, ...)
Indirectly calls the macro whose name is passed as the first
argument, with the remaining arguments passed as first, etc
arguments.
len(arg) Returns the number of characters in the first argument.
Extra arguments are ignored.
m4exit(code)
Immediately exits with the return value specified by the
first argument, 0 if none.
m4wrap(todo)
Allows you to define what happens at the final EOF, usually
for cleanup purposes. E.g.,
m4wrap(`cleanup(tempfile)')
causes the macro `cleanup' to be invoked after all other
processing is done.
Multiple calls to m4wrap() get inserted in sequence at the
final EOF.
maketemp(template)
Invokes mkstemp(3) on the first argument, and returns the
modified string. This can be used to create unique
temporary file names.
paste(file) 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 included.
patsubst(string, regexp, replacement)
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 corresponding back-reference.
popdef(arg, ...)
Restores the pushdefed definition for each argument.
pushdef(name, value)
Takes the same arguments as define, but it saves the
existing definition on a stack for later retrieval by
popdef().
regexp(string, regexp, replacement)
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 replaced.
shift(arg1, ...)
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.
sinclude(file)
Similar to include, except it ignores any errors.
spaste(file)
Similar to paste, except it ignores any errors.
substr(string, offset, length)
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.
syscmd(cmd) Passes the first argument to the shell. Nothing is
returned.
sysval Returns the return value from the last syscmd.
traceon(name, ...)
Enables tracing of macro expansions for the given arguments,
or for all macros if no argument is given.
traceoff(name, ...)
Disables tracing of macro expansions for the given
arguments, or for all macros if no argument is given.
translit(string, mapfrom, mapto)
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 tr(1) style abbreviations.
undefine(name, ...)
Removes the definition for the macros specified by its
arguments.
undivert(arg, ...)
Flushes the named output queues (or all queues if no
arguments).
unix A pre-defined macro for testing the OS platform.
__file__ Returns the current file's name.
__line__ Returns the current file's line number.
STANDARDS
The m4 utility is compliant with the IEEE Std 1003.1-2008 ("POSIX.1")
specification.
The flags -dgIot and the macros builtin, esyscmd, expr, format, indir,
paste, patsubst, regexp, spaste, unix, __file__, and __line__ are
extensions to that specification.
The output format of tracing and of dumpdef 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 GNU m4, to allow
autoconf to work.
The built-ins pushdef and popdef handle macro definitions as a stack.
However, define interacts with the stack in an undefined way. In this
implementation, define 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 m4.
Many other m4 have dire size limitations with respect to buffer sizes.
AUTHORS
Ozan Yigit <oz@sis.yorku.ca> and Richard A. O'Keefe
<ok@goanna.cs.rmit.OZ.AU>.
GNU m4 compatibility extensions by Marc Espie <espie@cvs.openbsd.org>.
NetBSD 10.99 June 25, 2020 NetBSD 10.99