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.\" @(#) $OpenBSD: m4.1,v 1.4 1997/02/12 23:32:31 deraadt Exp $
.\"
.\"
.Dd January 26, 1993
.Dt m4 1
.Os
.Sh NAME
.Nm m4
.Nd macro language processor
.Sh SYNOPSIS
.Nm m4
.Oo
.Fl D Ns Ar name Ns Op Ar =value
.Oc
.Op Fl U Ns Ar name
.Sh DESCRIPTION
The
.Nm 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).
.Nm m4
reads from the standard input and writes
the processed text to the standard output.
.Pp
Macro calls have the form name(argument1[, argument2, ...,] argumentN).
.Pp
There cannot be any space following the macro name and the open
parentheses '('. If the macro name is not followed by an open
parentheses it is processed with no arguments.
.Pp
Macro names consist of a leading alphabetic or underscore
possibly followed by alphanumeric or underscore characters, therefore
valid macro names match this pattern [a-zA-Z_][a-zA-Z0-9_]*.
.Pp
In arguments to macros, leading unquoted space, tab and newline
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.
.Pp
The options are as follows:
.Bl -tag -width "-Dname[=value]xxx"
.It Fl D Ns Ar name Ns Oo
.Ar =value
.Oc
Define the symbol
.Ar name
to have some value (or NULL).
.It Fl "U" Ns Ar "name"
Undefine the symbol
.Ar name .
.El
.Sh SYNTAX
.Nm m4
provides the following built-in macros. They may be
redefined, losing their original meaning.
Return values are NULL unless otherwise stated.
.Bl -tag -width changequotexxx
.It changecom
Change the start and end comment sequences. The default is
the pound sign `#' and the newline character. With no arguments
comments are turned off. The maximum length for a comment marker is
five characters.
.It 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 decr
Decrements the argument by 1. The argument must be a valid numeric string.
.It define
Define a new macro named by the first argument to have the
value of the second argument. 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.
.It defn
Returns the quoted definition for each argument. This can be used to rename
macro definitions (even for built-in macros).
.It divert
There are 10 output queues (numbered 0-9).
At the end of processing
.Nm 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).
.It divnum
Returns the current output queue number.
.It dnl
Discard input characters up to and including the next newline.
.It dumpdef
Prints the names and definitions for the named items, or for everything
if no arguments are passed.
.It errprint
Prints the first argument on the standard error output stream.
.It 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 expr
This is an alias for eval.
.It 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 NULL. The word `unix' is predefined.
.It ifelse
If the first argument matches the second argument then 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 NULL is
returned if no other matches were found.
.It include
Returns the contents of the file specified in the first argument.
Include aborts with an error message if the file cannot be included.
.It incr
Increments the argument by 1. The argument must be a valid numeric string.
.It index
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.
.It len
Returns the number of characters in the first argument. Extra arguments
are ignored.
.It m4exit
Immediately exits with the return value specified by the first argument,
0 if none.
.It m4wrap
Allows you to define what happens at the final EOF, usually for cleanup
purposes (e.g., m4wrap("cleanup(tempfile)") causes the macro cleanup to
invoked after all other processing is done.)
.It maketemp
Translates the string 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 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 popdef
Restores the pushdef'ed definition for each argument.
.It pushdef
Takes the same arguments as define, but it saves the definition on a
stack for later retrieval by popdef.
.It 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 sinclude
Similar to include, except it ignores any errors.
.It spaste
Similar to paste, except it ignores any errors.
.It 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 syscmd
Passes the first argument to the shell. Nothing is returned.
.It sysval
Returns the return value from the last syscmd.
.It 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 undefine
Removes the definition for the macro specified by the first argument.
.It undivert
Flushes the named output queues (or all queues if no arguments).
.It unix
A pre-defined macro for testing the OS platform.
.El
.Sh AUTHOR
Ozan Yigit <oz@sis.yorku.ca> and Richard A. O'Keefe (ok@goanna.cs.rmit.OZ.AU)
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