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.\"	@(#) $OpenBSD: m4.1,v 1.24 2002/04/18 18:57:23 espie Exp $
.\" $FreeBSD: release/9.1.0/usr.bin/m4/m4.1 140368 2005-01-17 07:44:44Z ru $
.\"
.Dd July 3, 2004
.Dt M4 1
.Os
.Sh NAME
.Nm m4
.Nd macro language processor
.Sh SYNOPSIS
.Nm
.Op Fl d Ar flags
.Op Fl t Ar name
.Op Fl gs
.Op Fl D Ar name Ns Op = Ns Ar value
.Op Fl U Ar name
.Op Fl I Ar dirname
.Op Ar
.Sh DESCRIPTION
The
.Nm
utility is a macro processor that can be used as a front end to any
language (e.g., C, ratfor, fortran, lex, and yacc).
The
.Nm
utility reads from the standard input and writes
the processed text to the standard output.
.Pp
Macro calls have the form
.Ic name Ns Pq Ar argument1 Ns Op , Ar argument2 , ... , argumentN .
.Pp
There cannot be any space following the macro name and the open
parenthesis
.Pq Ql \&( .
If the macro name is not followed by an open
parenthesis it is processed with no arguments.
.Pp
Macro names consist of a leading alphabetic or underscore
possibly followed by alphanumeric or underscore characters, e.g.,
valid macro names match the pattern
.Dq Li [a-zA-Z_][a-zA-Z0-9_]* .
.Pp
In arguments to macros, leading unquoted space, tab, and newline
.Pq Ql \en
characters are ignored.
To quote strings, use left and right single
quotes (e.g.,
.Sq "\ this is a string with a leading space" ) .
You can change the quote characters with the
.Ic changequote
built-in macro.
.Pp
Most built-ins do not make any sense without arguments, and hence are not
recognized as special when not followed by an open parenthesis.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl s
Emit
.Ic #line
directives for
.Xr cpp 1 .
.It Fl D Ar name Ns Op = Ns Ar value
Define the symbol
.Ar name
to have some value (or
.Dv NULL ) .
.It Fl U Ar name
Undefine the symbol
.Ar name .
.It Fl I Ar dirname
Add directory
.Ar dirname
to the include path.
.It Fl d Ar flags
Set trace flags.
The
.Ar flags
argument may hold the following:
.Pp
.Bl -tag -width indent -compact
.It Cm a
print macro arguments
.It Cm c
print macro expansion over several lines
.It Cm e
print result of macro expansion
.It Cm f
print filename location
.It Cm l
print line number
.It Cm q
quote arguments and expansion with the current quotes
.It Cm t
start with all macros traced
.It Cm x
number macro expansions
.It Cm V
turn on all options
.El
.Pp
By default, trace is set to
.Cm eq .
.It Fl t Ar macro
Turn tracing on for
.Ar macro .
.It Fl g
Activate GNU-m4 compatibility mode.
In this mode,
.Ic changequote
with two empty parameters deactivates quotes,
.Ic translit
handles simple character ranges (e.g.,
.Li a-z ) ,
regular expressions mimic
.Xr emacs 1
behavior,
and the number of diversions is unlimited.
.El
.Sh SYNTAX
The
.Nm
utility provides the following built-in macros.
They may be redefined, losing their original meaning.
Return values are null unless otherwise stated.
.Bl -tag -width ".Ic changequote"
.It Ic builtin
Calls a built-in by its name, overriding possible redefinitions.
.It Ic changecom
Changes the start and end comment sequences.
The default is the pound sign
.Pq Ql #
and the newline character.
With no arguments, the comment sequence is reset to the default,
in GNU
.Nm
mode, comments are turned off.
The maximum length for a comment marker is five characters.
.It Ic changequote
Defines the quote symbols to be the first and second arguments.
The symbols may be up to five characters long.
If no arguments are
given it restores the default open and close single quotes.
.It Ic decr
Decrements the argument by 1.
The argument must be a valid numeric string.
.It Ic define
Define a new macro named by the first argument to have the
value of the second argument.
Each occurrence of
.Sq Li $ Ns Ar n
(where
.Ar n
is 0 through 9) is replaced by the
.Ar n Ns 'th
argument.
.Ql $0
is the name of the calling macro.
Undefined arguments are replaced by a null string.
.Ql $#
is replaced by the number of arguments;
.Ql $*
is replaced by all arguments comma separated;
.Ql $@
is the same as
.Ql $*
but all arguments are quoted against further expansion.
.It Ic defn
Returns the quoted definition for each argument.
This can be used to rename
macro definitions (even for built-in macros).
.It Ic divert
There are 10 output queues (numbered 0-9).
At the end of processing
.Nm
concatenates all the queues in numerical order to produce the
final output.
Initially the output queue is 0.
The
.Ic divert
macro allows you to select a new output queue (an invalid argument
passed to
.Ic divert
causes output to be discarded).
.It Ic divnum
Returns the current output queue number.
.It Ic dnl
Discards input characters up to and including the next newline.
.It Ic dumpdef
Prints the names and definitions for the named items, or for everything
if no arguments are passed.
.It Ic errprint
Prints the first argument on the standard error output stream.
.It Ic esyscmd
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
.Nm .
.It Ic eval
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 second argument (if any)
specifies the radix for the result, and the third argument (if any)
specifies the minimum number of digits in the result.
.It Ic expr
This is an alias for
.Ic eval .
.It Ic ifdef
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
.Dv NULL .
The word
.Ic unix
is predefined.
.It Ic ifelse
If the first argument matches the second argument then
.Ic ifelse
returns
the third argument.
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
.Dv NULL
is returned if no other matches were found.
.It Ic include
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
.Fl I
on the command line, then the environment variable
.Ev M4PATH ,
as a colon-separated list of directories.
Aborts with an error message if the file cannot be included.
.It Ic incr
Increments the argument by 1.
The argument must be a valid numeric string.
.It Ic index
Returns the index of the second argument in the first argument (e.g.,
.Fn index "the quick brown fox jumped" fox
returns 16).
If the second
argument is not found,
.Ic index
returns \-1.
.It Ic indir
Indirectly calls the macro whose name is passed as the first arguments,
with the remaining arguments passed as first, etc.\& arguments.
.It Ic len
Returns the number of characters in the first argument.
Extra arguments
are ignored.
.It Ic m4exit
Immediately exits with the return value specified by the first argument,
0 if none.
.It Ic m4wrap
Allows you to define what happens at the final
.Dv EOF ,
usually for cleanup purposes (e.g.,
.Fn m4wrap cleanup(tempfile)
causes the macro
.Ic cleanup
to be
invoked after all other processing is done).
.It Ic maketemp
Translates the string
.Dq Li XXXXX
in the first argument with the current process
ID leaving other characters alone.
This can be used to create unique
temporary file names.
.It Ic paste
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.
.It Ic patsubst
Substitutes a regular expression in a string with a replacement string.
Usual substitution patterns apply: an ampersand
.Pq Ql &
is replaced by the string matching the regular expression.
The string
.Sq \e Ns Ar # ,
where
.Ar #
is a digit, is replaced by the corresponding back-reference.
.It Ic popdef
Restores the
.Ic pushdef Ns ed
definition for each argument.
.It Ic pushdef
Takes the same arguments as
.Ic define ,
but it saves the definition on a
stack for later retrieval by
.Ic popdef .
.It Ic regexp
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.
.It Ic shift
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.
.It Ic sinclude
Similar to
.Ic include ,
except it ignores any errors.
.It Ic spaste
Similar to
.Ic paste ,
except it ignores any errors.
.It Ic substr
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.
.It Ic syscmd
Passes the first argument to the shell.
Nothing is returned.
.It Ic sysval
Returns the return value from the last
.Ic syscmd .
.It Ic traceon
Enables tracing of macro expansions for the given arguments, or for all
macros if no argument is given.
.It Ic traceoff
Disables tracing of macro expansions for the given arguments, or for all
macros if no argument is given.
.It Ic translit
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
.Xr tr 1
style abbreviations.
.It Ic undefine
Removes the definition for the macros specified by its arguments.
.It Ic undivert
Flushes the named output queues (or all queues if no arguments).
.It Ic unix
A pre-defined macro for testing the OS platform.
.It Ic __line__
Returns the current file's line number.
.It Ic __file__
Returns the current file's name.
.El
.Sh EXIT STATUS
.Ex -std
.Pp
The
.Ic m4exit
macro may be used to change the exit status from the input file.
.Sh COMPATIBILITY
The
.Nm
utility follows the
.St -susv2 ,
along with a few extensions taken from GNU-m4.
Flags
.Fl I , d ,
and
.Fl t
are non-standard.
.Pp
The output format of tracing and of
.Ic dumpdef
are not specified in any standard,
are likely to change and should not be relied upon.
The current format of tracing is closely modeled on GNU-m4,
to allow
.Nm autoconf
to work.
.Pp
For portability, one should not use the macros
.Ic builtin ,
.Ic esyscmd ,
.Ic expr ,
.Ic indir ,
.Ic paste ,
.Ic patsubst ,
.Ic regexp ,
.Ic spaste ,
.Ic unix ,
.Ic __line__ ,
and
.Ic __file__ .
.Pp
All built-ins do expand without arguments in many other
.Nm
implementations.
.Pp
Many other
.Nm
implementations have dire size limitations with respect to buffer sizes.
.Sh STANDARDS
The
.Nm
utility
conforms to
.St -p1003.1-2001 .
.Sh HISTORY
An
.Nm
command appeared in PWB UNIX.
.Sh AUTHORS
.An -nosplit
.An Ozan Yigit Aq oz@sis.yorku.ca
and
.An Richard A. O'Keefe Aq ok@goanna.cs.rmit.OZ.AU .
GNU-m4 compatibility extensions by
.An Marc Espie Aq espie@cvs.openbsd.org .
.Sh BUGS
The
.Nm
utility does not recognize multibyte characters.