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20 KiB
Plaintext
.\" Copyright (C) Caldera International Inc. 2001-2002. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions are
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.\" met:
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.\"
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.\" Redistributions of source code and documentation must retain the above
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.\" copyright notice, this list of conditions and the following
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.\" disclaimer.
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.\"
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.\" Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\"
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.\" This product includes software developed or owned by Caldera
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.\" International, Inc. Neither the name of Caldera International, Inc.
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.\" nor the names of other contributors may be used to endorse or promote
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.\" products derived from this software without specific prior written
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.\" permission.
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.\"
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.\" USE OF THE SOFTWARE PROVIDED FOR UNDER THIS LICENSE BY CALDERA
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.\" INTERNATIONAL, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL CALDERA INTERNATIONAL, INC. BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) RISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
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.\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" @(#)m4.ms 6.3 (Berkeley) 6/5/93
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.\"
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.\" $FreeBSD$
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.de MH
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Bell Laboratories, Murray Hill, NJ 07974.
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..
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.EH 'PSD:17-%''The M4 Macro Processor'
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.OH 'The M4 Macro Processor''PSD:17-%'
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.if n .ls 2
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.tr _\(em
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.tr *\(**
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.de UC
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\&\\$3\s-1\\$1\\s0\&\\$2
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..
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.de IT
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.de UL
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.if n .ul
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\&\\$3\f3\\$1\fP\&\\$2
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.if t .ta .4i .8i 1.2i 1.6i 2i 2.4i 2.8i 3.2i 3.6i 4i 4.4i 4.8i 5.2i 5.6i
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.if t .tr -\(mi|\(bv'\(fm^\(no*\(**
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.if t .tr _\(ul
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.lg 0
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..
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.de P2
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.ps \\n(PS
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.vs \\n(VSp
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.ft R
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.if n .ls 2
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.tr --||''^^!!
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.if t .tr _\(em
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.fi
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.lg
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.DE
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.if t .tr _\(em
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..
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.hw semi-colon
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.hw estab-lished
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.hy 14
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. \"2=not last lines; 4= no -xx; 8=no xx-
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. \"special chars in programs
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. \" start of text
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.\".RP
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.\" .....TR 59
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.\" .....TM 77-1273-6 39199 39199-11
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.ND "July 1, 1977"
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.TL
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The M4 Macro Processor
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.AU "MH 2C-518" 6021
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Brian W. Kernighan
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.AU "MH 2C-517" 3770
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Dennis M. Ritchie
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.AI
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.MH
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.AB
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.PP
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|
M4 is a macro processor available on
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.UX
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and
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.UC GCOS .
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Its primary use has been as a
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front end for Ratfor for those
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cases where parameterless macros
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are not adequately powerful.
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It has also been used for languages as disparate as C and Cobol.
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M4 is particularly suited for functional languages like Fortran, PL/I and C
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since macros are specified in a functional notation.
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.PP
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M4 provides features seldom found even in much larger
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macro processors,
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including
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.IP " \(bu"
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arguments
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.IP " \(bu"
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condition testing
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.IP " \(bu"
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arithmetic capabilities
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.IP " \(bu"
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string and substring functions
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.IP " \(bu"
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file manipulation
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.LP
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.PP
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This paper is a user's manual for M4.
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.AE
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|
.\" .CS 6 0 6 0 0 1
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.if t .2C
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.SH
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Introduction
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.PP
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A macro processor is a useful way to enhance a programming language,
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|
to make it more palatable
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or more readable,
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or to tailor it to a particular application.
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|
The
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.UL #define
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|
statement in C
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|
and the analogous
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.UL define
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|
in Ratfor
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|
are examples of the basic facility provided by
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any macro processor _
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|
replacement of text by other text.
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.PP
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|
The M4 macro processor is an extension of a macro processor called M3
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|
which was written by D. M. Ritchie
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|
for the AP-3 minicomputer;
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|
M3 was in turn based on a macro processor implemented for [1].
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|
Readers unfamiliar with the basic ideas of macro processing
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|
may wish to read some of the discussion there.
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|
.PP
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|
M4 is a suitable front end for Ratfor and C,
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|
and has also been used successfully with Cobol.
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|
Besides the straightforward replacement of one string of text by another,
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it provides
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macros with arguments,
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|
conditional macro expansion,
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arithmetic,
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file manipulation,
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and some specialized string processing functions.
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.PP
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|
The basic operation of M4
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|
is to copy its input to its output.
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As the input is read, however, each alphanumeric ``token''
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(that is, string of letters and digits) is checked.
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|
If it is the name of a macro,
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|
then the name of the macro is replaced by its defining text,
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and the resulting string is pushed back onto the
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input to be rescanned.
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|
Macros may be called with arguments, in which case the arguments are collected
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|
and substituted into the right places in the defining text
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|
before it is rescanned.
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.PP
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|
M4 provides a collection of about twenty built-in
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macros
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|
which perform various useful operations;
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|
in addition, the user can define new macros.
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|
Built-ins and user-defined macros work exactly the same way, except that
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|
some of the built-in macros have side effects
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|
on the state of the process.
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|
.SH
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|
Usage
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.PP
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|
On
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.UC UNIX ,
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|
use
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.P1
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m4 [files]
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.P2
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|
Each argument file is processed in order;
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|
if there are no arguments, or if an argument
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is `\-',
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|
the standard input is read at that point.
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|
The processed text is written on the standard output,
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|
which may be captured for subsequent processing with
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.P1
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|
m4 [files] >outputfile
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.P2
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|
On
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.UC GCOS ,
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|
usage is identical, but the program is called
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.UL \&./m4 .
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|
.SH
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|
Defining Macros
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|
.PP
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|
The primary built-in function of M4
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|
is
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|
.UL define ,
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|
which is used to define new macros.
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|
The input
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.P1
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|
define(name, stuff)
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.P2
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|
causes the string
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|
.UL name
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|
to be defined as
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|
.UL stuff .
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|
All subsequent occurrences of
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.UL name
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|
will be replaced by
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|
.UL stuff .
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.UL name
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must be alphanumeric and must begin with a letter
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|
(the underscore \(ul counts as a letter).
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|
.UL stuff
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|
is any text that contains balanced parentheses;
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|
it may stretch over multiple lines.
|
|
.PP
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|
Thus, as a typical example,
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|
.P1
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|
define(N, 100)
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|
...
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|
if (i > N)
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|
.P2
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|
defines
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|
.UL N
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|
to be 100, and uses this ``symbolic constant'' in a later
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|
.UL if
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|
statement.
|
|
.PP
|
|
The left parenthesis must immediately follow the word
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|
.UL define ,
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|
to signal that
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|
.UL define
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|
has arguments.
|
|
If a macro or built-in name is not followed immediately by `(',
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|
it is assumed to have no arguments.
|
|
This is the situation for
|
|
.UL N
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|
above;
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|
it is actually a macro with no arguments,
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|
and thus when it is used there need be no (...) following it.
|
|
.PP
|
|
You should also notice that a macro name is only recognized as such
|
|
if it appears surrounded by non-alphanumerics.
|
|
For example, in
|
|
.P1
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|
define(N, 100)
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|
...
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|
if (NNN > 100)
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|
.P2
|
|
the variable
|
|
.UL NNN
|
|
is absolutely unrelated to the defined macro
|
|
.UL N ,
|
|
even though it contains a lot of
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|
.UL N 's.
|
|
.PP
|
|
Things may be defined in terms of other things.
|
|
For example,
|
|
.P1
|
|
define(N, 100)
|
|
define(M, N)
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|
.P2
|
|
defines both M and N to be 100.
|
|
.PP
|
|
What happens if
|
|
.UL N
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|
is redefined?
|
|
Or, to say it another way, is
|
|
.UL M
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|
defined as
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|
.UL N
|
|
or as 100?
|
|
In M4,
|
|
the latter is true _
|
|
.UL M
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|
is 100, so even if
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|
.UL N
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|
subsequently changes,
|
|
.UL M
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|
does not.
|
|
.PP
|
|
This behavior arises because
|
|
M4 expands macro names into their defining text as soon as it possibly can.
|
|
Here, that means that when the string
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|
.UL N
|
|
is seen as the arguments of
|
|
.UL define
|
|
are being collected, it is immediately replaced by 100;
|
|
it's just as if you had said
|
|
.P1
|
|
define(M, 100)
|
|
.P2
|
|
in the first place.
|
|
.PP
|
|
If this isn't what you really want, there are two ways out of it.
|
|
The first, which is specific to this situation,
|
|
is to interchange the order of the definitions:
|
|
.P1
|
|
define(M, N)
|
|
define(N, 100)
|
|
.P2
|
|
Now
|
|
.UL M
|
|
is defined to be the string
|
|
.UL N ,
|
|
so when you ask for
|
|
.UL M
|
|
later, you'll always get the value of
|
|
.UL N
|
|
at that time
|
|
(because the
|
|
.UL M
|
|
will be replaced by
|
|
.UL N
|
|
which will be replaced by 100).
|
|
.SH
|
|
Quoting
|
|
.PP
|
|
The more general solution is to delay the expansion of
|
|
the arguments of
|
|
.UL define
|
|
by
|
|
.ul
|
|
quoting
|
|
them.
|
|
Any text surrounded by the single quotes \(ga and \(aa
|
|
is not expanded immediately, but has the quotes stripped off.
|
|
If you say
|
|
.P1
|
|
define(N, 100)
|
|
define(M, `N')
|
|
.P2
|
|
the quotes around the
|
|
.UL N
|
|
are stripped off as the argument is being collected,
|
|
but they have served their purpose, and
|
|
.UL M
|
|
is defined as
|
|
the string
|
|
.UL N ,
|
|
not 100.
|
|
The general rule is that M4 always strips off
|
|
one level of single quotes whenever it evaluates
|
|
something.
|
|
This is true even outside of
|
|
macros.
|
|
If you want the word
|
|
.UL define
|
|
to appear in the output,
|
|
you have to quote it in the input,
|
|
as in
|
|
.P1
|
|
`define' = 1;
|
|
.P2
|
|
.PP
|
|
As another instance of the same thing, which is a bit more surprising,
|
|
consider redefining
|
|
.UL N :
|
|
.P1
|
|
define(N, 100)
|
|
...
|
|
define(N, 200)
|
|
.P2
|
|
Perhaps regrettably, the
|
|
.UL N
|
|
in the second definition is
|
|
evaluated as soon as it's seen;
|
|
that is, it is
|
|
replaced by
|
|
100, so it's as if you had written
|
|
.P1
|
|
define(100, 200)
|
|
.P2
|
|
This statement is ignored by M4, since you can only define things that look
|
|
like names, but it obviously doesn't have the effect you wanted.
|
|
To really redefine
|
|
.UL N ,
|
|
you must delay the evaluation by quoting:
|
|
.P1
|
|
define(N, 100)
|
|
...
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|
define(`N', 200)
|
|
.P2
|
|
In M4,
|
|
it is often wise to quote the first argument of a macro.
|
|
.PP
|
|
If \` and \' are not convenient for some reason,
|
|
the quote characters can be changed with the built-in
|
|
.UL changequote :
|
|
.P1
|
|
changequote([, ])
|
|
.P2
|
|
makes the new quote characters the left and right brackets.
|
|
You can restore the original characters with just
|
|
.P1
|
|
changequote
|
|
.P2
|
|
.PP
|
|
There are two additional built-ins related to
|
|
.UL define .
|
|
.UL undefine
|
|
removes the definition of some macro or built-in:
|
|
.P1
|
|
undefine(`N')
|
|
.P2
|
|
removes the definition of
|
|
.UL N .
|
|
(Why are the quotes absolutely necessary?)
|
|
Built-ins can be removed with
|
|
.UL undefine ,
|
|
as in
|
|
.P1
|
|
undefine(`define')
|
|
.P2
|
|
but once you remove one, you can never get it back.
|
|
.PP
|
|
The built-in
|
|
.UL ifdef
|
|
provides a way to determine if a macro is currently defined.
|
|
In particular, M4 has pre-defined the names
|
|
.UL unix
|
|
and
|
|
.UL gcos
|
|
on the corresponding systems, so you can
|
|
tell which one you're using:
|
|
.P1
|
|
ifdef(`unix', `define(wordsize,16)' )
|
|
ifdef(`gcos', `define(wordsize,36)' )
|
|
.P2
|
|
makes a definition appropriate for the particular machine.
|
|
Don't forget the quotes!
|
|
.PP
|
|
.UL ifdef
|
|
actually permits three arguments;
|
|
if the name is undefined, the value of
|
|
.UL ifdef
|
|
is then the third argument, as in
|
|
.P1
|
|
ifdef(`unix', on UNIX, not on UNIX)
|
|
.P2
|
|
.SH
|
|
Arguments
|
|
.PP
|
|
So far we have discussed the simplest form of macro processing _
|
|
replacing one string by another (fixed) string.
|
|
User-defined macros may also have arguments, so different invocations
|
|
can have different results.
|
|
Within the replacement text for a macro
|
|
(the second argument of its
|
|
.UL define )
|
|
any occurrence of
|
|
.UL $n
|
|
will be replaced by the
|
|
.UL n th
|
|
argument when the macro
|
|
is actually used.
|
|
Thus, the macro
|
|
.UL bump ,
|
|
defined as
|
|
.P1
|
|
define(bump, $1 = $1 + 1)
|
|
.P2
|
|
generates code to increment its argument by 1:
|
|
.P1
|
|
bump(x)
|
|
.P2
|
|
is
|
|
.P1
|
|
x = x + 1
|
|
.P2
|
|
.PP
|
|
A macro can have as many arguments as you want,
|
|
but only the first nine are accessible,
|
|
through
|
|
.UL $1
|
|
to
|
|
.UL $9 .
|
|
(The macro name itself is
|
|
.UL $0 ,
|
|
although that is less commonly used.)
|
|
Arguments that are not supplied are replaced by null strings,
|
|
so
|
|
we can define a macro
|
|
.UL cat
|
|
which simply concatenates its arguments, like this:
|
|
.P1
|
|
define(cat, $1$2$3$4$5$6$7$8$9)
|
|
.P2
|
|
Thus
|
|
.P1
|
|
cat(x, y, z)
|
|
.P2
|
|
is equivalent to
|
|
.P1
|
|
xyz
|
|
.P2
|
|
.UL $4
|
|
through
|
|
.UL $9
|
|
are null, since no corresponding arguments were provided.
|
|
.PP
|
|
.PP
|
|
Leading unquoted blanks, tabs, or newlines that occur during argument collection
|
|
are discarded.
|
|
All other white space is retained.
|
|
Thus
|
|
.P1
|
|
define(a, b c)
|
|
.P2
|
|
defines
|
|
.UL a
|
|
to be
|
|
.UL b\ \ \ c .
|
|
.PP
|
|
Arguments are separated by commas, but parentheses are counted properly,
|
|
so a comma ``protected'' by parentheses does not terminate an argument.
|
|
That is, in
|
|
.P1
|
|
define(a, (b,c))
|
|
.P2
|
|
there are only two arguments;
|
|
the second is literally
|
|
.UL (b,c) .
|
|
And of course a bare comma or parenthesis can be inserted by quoting it.
|
|
.SH
|
|
Arithmetic Built-ins
|
|
.PP
|
|
M4 provides two built-in functions for doing arithmetic
|
|
on integers (only).
|
|
The simplest is
|
|
.UL incr ,
|
|
which increments its numeric argument by 1.
|
|
Thus to handle the common programming situation
|
|
where you want a variable to be defined as ``one more than N'',
|
|
write
|
|
.P1
|
|
define(N, 100)
|
|
define(N1, `incr(N)')
|
|
.P2
|
|
Then
|
|
.UL N1
|
|
is defined as one more than the current value of
|
|
.UL N .
|
|
.PP
|
|
The more general mechanism for arithmetic is a built-in
|
|
called
|
|
.UL eval ,
|
|
which is capable of arbitrary arithmetic on integers.
|
|
It provides the operators
|
|
(in decreasing order of precedence)
|
|
.DS
|
|
unary + and \(mi
|
|
** or ^ (exponentiation)
|
|
* / % (modulus)
|
|
+ \(mi
|
|
== != < <= > >=
|
|
! (not)
|
|
& or && (logical and)
|
|
\(or or \(or\(or (logical or)
|
|
.DE
|
|
Parentheses may be used to group operations where needed.
|
|
All the operands of
|
|
an expression given to
|
|
.UL eval
|
|
must ultimately be numeric.
|
|
The numeric value of a true relation
|
|
(like 1>0)
|
|
is 1, and false is 0.
|
|
The precision in
|
|
.UL eval
|
|
is
|
|
32 bits on
|
|
.UC UNIX
|
|
and 36 bits on
|
|
.UC GCOS .
|
|
.PP
|
|
As a simple example, suppose we want
|
|
.UL M
|
|
to be
|
|
.UL 2**N+1 .
|
|
Then
|
|
.P1
|
|
define(N, 3)
|
|
define(M, `eval(2**N+1)')
|
|
.P2
|
|
As a matter of principle, it is advisable
|
|
to quote the defining text for a macro
|
|
unless it is very simple indeed
|
|
(say just a number);
|
|
it usually gives the result you want,
|
|
and is a good habit to get into.
|
|
.SH
|
|
File Manipulation
|
|
.PP
|
|
You can include a new file in the input at any time by
|
|
the built-in function
|
|
.UL include :
|
|
.P1
|
|
include(filename)
|
|
.P2
|
|
inserts the contents of
|
|
.UL filename
|
|
in place of the
|
|
.UL include
|
|
command.
|
|
The contents of the file is often a set of definitions.
|
|
The value
|
|
of
|
|
.UL include
|
|
(that is, its replacement text)
|
|
is the contents of the file;
|
|
this can be captured in definitions, etc.
|
|
.PP
|
|
It is a fatal error if the file named in
|
|
.UL include
|
|
cannot be accessed.
|
|
To get some control over this situation, the alternate form
|
|
.UL sinclude
|
|
can be used;
|
|
.UL sinclude
|
|
(``silent include'')
|
|
says nothing and continues if it can't access the file.
|
|
.PP
|
|
It is also possible to divert the output of M4 to temporary files during processing,
|
|
and output the collected material upon command.
|
|
M4 maintains nine of these diversions, numbered 1 through 9.
|
|
If you say
|
|
.P1
|
|
divert(n)
|
|
.P2
|
|
all subsequent output is put onto the end of a temporary file
|
|
referred to as
|
|
.UL n .
|
|
Diverting to this file is stopped by another
|
|
.UL divert
|
|
command;
|
|
in particular,
|
|
.UL divert
|
|
or
|
|
.UL divert(0)
|
|
resumes the normal output process.
|
|
.PP
|
|
Diverted text is normally output all at once
|
|
at the end of processing,
|
|
with the diversions output in numeric order.
|
|
It is possible, however, to bring back diversions
|
|
at any time,
|
|
that is, to append them to the current diversion.
|
|
.P1
|
|
undivert
|
|
.P2
|
|
brings back all diversions in numeric order, and
|
|
.UL undivert
|
|
with arguments brings back the selected diversions
|
|
in the order given.
|
|
The act of undiverting discards the diverted stuff,
|
|
as does diverting into a diversion
|
|
whose number is not between 0 and 9 inclusive.
|
|
.PP
|
|
The value of
|
|
.UL undivert
|
|
is
|
|
.ul
|
|
not
|
|
the diverted stuff.
|
|
Furthermore, the diverted material is
|
|
.ul
|
|
not
|
|
rescanned for macros.
|
|
.PP
|
|
The built-in
|
|
.UL divnum
|
|
returns the number of the currently active diversion.
|
|
This is zero during normal processing.
|
|
.SH
|
|
System Command
|
|
.PP
|
|
You can run any program in the local operating system
|
|
with the
|
|
.UL syscmd
|
|
built-in.
|
|
For example,
|
|
.P1
|
|
syscmd(date)
|
|
.P2
|
|
on
|
|
.UC UNIX
|
|
runs the
|
|
.UL date
|
|
command.
|
|
Normally
|
|
.UL syscmd
|
|
would be used to create a file
|
|
for a subsequent
|
|
.UL include .
|
|
.PP
|
|
To facilitate making unique file names, the built-in
|
|
.UL maketemp
|
|
is provided, with specifications identical to the system function
|
|
.ul
|
|
mktemp:
|
|
a string of XXXXX in the argument is replaced
|
|
by the process id of the current process.
|
|
.SH
|
|
Conditionals
|
|
.PP
|
|
There is a built-in called
|
|
.UL ifelse
|
|
which enables you to perform arbitrary conditional testing.
|
|
In the simplest form,
|
|
.P1
|
|
ifelse(a, b, c, d)
|
|
.P2
|
|
compares the two strings
|
|
.UL a
|
|
and
|
|
.UL b .
|
|
If these are identical,
|
|
.UL ifelse
|
|
returns
|
|
the string
|
|
.UL c ;
|
|
otherwise it returns
|
|
.UL d .
|
|
Thus we might define a macro called
|
|
.UL compare
|
|
which compares two strings and returns ``yes'' or ``no''
|
|
if they are the same or different.
|
|
.P1
|
|
define(compare, `ifelse($1, $2, yes, no)')
|
|
.P2
|
|
Note the quotes,
|
|
which prevent too-early evaluation of
|
|
.UL ifelse .
|
|
.PP
|
|
If the fourth argument is missing, it is treated as empty.
|
|
.PP
|
|
.UL ifelse
|
|
can actually have any number of arguments,
|
|
and thus provides a limited form of multi-way decision capability.
|
|
In the input
|
|
.P1
|
|
ifelse(a, b, c, d, e, f, g)
|
|
.P2
|
|
if the string
|
|
.UL a
|
|
matches the string
|
|
.UL b ,
|
|
the result is
|
|
.UL c .
|
|
Otherwise, if
|
|
.UL d
|
|
is the same as
|
|
.UL e ,
|
|
the result is
|
|
.UL f .
|
|
Otherwise the result is
|
|
.UL g .
|
|
If the final argument
|
|
is omitted, the result is null,
|
|
so
|
|
.P1
|
|
ifelse(a, b, c)
|
|
.P2
|
|
is
|
|
.UL c
|
|
if
|
|
.UL a
|
|
matches
|
|
.UL b ,
|
|
and null otherwise.
|
|
.SH
|
|
String Manipulation
|
|
.PP
|
|
The built-in
|
|
.UL len
|
|
returns the length of the string that makes up its argument.
|
|
Thus
|
|
.P1
|
|
len(abcdef)
|
|
.P2
|
|
is 6, and
|
|
.UL len((a,b))
|
|
is 5.
|
|
.PP
|
|
The built-in
|
|
.UL substr
|
|
can be used to produce substrings of strings.
|
|
.UL substr(s,\ i,\ n)
|
|
returns the substring of
|
|
.UL s
|
|
that starts at the
|
|
.UL i th
|
|
position
|
|
(origin zero),
|
|
and is
|
|
.UL n
|
|
characters long.
|
|
If
|
|
.UL n
|
|
is omitted, the rest of the string is returned,
|
|
so
|
|
.P1
|
|
substr(`now is the time', 1)
|
|
.P2
|
|
is
|
|
.P1
|
|
ow is the time
|
|
.P2
|
|
If
|
|
.UL i
|
|
or
|
|
.UL n
|
|
are out of range, various sensible things happen.
|
|
.PP
|
|
.UL index(s1,\ s2)
|
|
returns the index (position) in
|
|
.UL s1
|
|
where the string
|
|
.UL s2
|
|
occurs, or \-1
|
|
if it doesn't occur.
|
|
As with
|
|
.UL substr ,
|
|
the origin for strings is 0.
|
|
.PP
|
|
The built-in
|
|
.UL translit
|
|
performs character transliteration.
|
|
.P1
|
|
translit(s, f, t)
|
|
.P2
|
|
modifies
|
|
.UL s
|
|
by replacing any character found in
|
|
.UL f
|
|
by the corresponding character of
|
|
.UL t .
|
|
That is,
|
|
.P1
|
|
translit(s, aeiou, 12345)
|
|
.P2
|
|
replaces the vowels by the corresponding digits.
|
|
If
|
|
.UL t
|
|
is shorter than
|
|
.UL f ,
|
|
characters which don't have an entry in
|
|
.UL t
|
|
are deleted; as a limiting case,
|
|
if
|
|
.UL t
|
|
is not present at all,
|
|
characters from
|
|
.UL f
|
|
are deleted from
|
|
.UL s .
|
|
So
|
|
.P1
|
|
translit(s, aeiou)
|
|
.P2
|
|
deletes vowels from
|
|
.UL s .
|
|
.PP
|
|
There is also a built-in called
|
|
.UL dnl
|
|
which deletes all characters that follow it up to
|
|
and including the next newline;
|
|
it is useful mainly for throwing away
|
|
empty lines that otherwise tend to clutter up M4 output.
|
|
For example, if you say
|
|
.P1
|
|
define(N, 100)
|
|
define(M, 200)
|
|
define(L, 300)
|
|
.P2
|
|
the newline at the end of each line is not part of the definition,
|
|
so it is copied into the output, where it may not be wanted.
|
|
If you add
|
|
.UL dnl
|
|
to each of these lines, the newlines will disappear.
|
|
.PP
|
|
Another way to achieve this, due to J. E. Weythman,
|
|
is
|
|
.P1
|
|
divert(-1)
|
|
define(...)
|
|
...
|
|
divert
|
|
.P2
|
|
.SH
|
|
Printing
|
|
.PP
|
|
The built-in
|
|
.UL errprint
|
|
writes its arguments out on the standard error file.
|
|
Thus you can say
|
|
.P1
|
|
errprint(`fatal error')
|
|
.P2
|
|
.PP
|
|
.UL dumpdef
|
|
is a debugging aid which
|
|
dumps the current definitions of defined terms.
|
|
If there are no arguments, you get everything;
|
|
otherwise you get the ones you name as arguments.
|
|
Don't forget to quote the names!
|
|
.SH
|
|
Summary of Built-ins
|
|
.PP
|
|
Each entry is preceded by the
|
|
page number where it is described.
|
|
.DS
|
|
.tr '\'`\`
|
|
.ta .25i
|
|
3 changequote(L, R)
|
|
1 define(name, replacement)
|
|
4 divert(number)
|
|
4 divnum
|
|
5 dnl
|
|
5 dumpdef(`name', `name', ...)
|
|
5 errprint(s, s, ...)
|
|
4 eval(numeric expression)
|
|
3 ifdef(`name', this if true, this if false)
|
|
5 ifelse(a, b, c, d)
|
|
4 include(file)
|
|
3 incr(number)
|
|
5 index(s1, s2)
|
|
5 len(string)
|
|
4 maketemp(...XXXXX...)
|
|
4 sinclude(file)
|
|
5 substr(string, position, number)
|
|
4 syscmd(s)
|
|
5 translit(str, from, to)
|
|
3 undefine(`name')
|
|
4 undivert(number,number,...)
|
|
.DE
|
|
.SH
|
|
Acknowledgements
|
|
.PP
|
|
We are indebted to Rick Becker, John Chambers,
|
|
Doug McIlroy,
|
|
and especially Jim Weythman,
|
|
whose pioneering use of M4 has led to several valuable improvements.
|
|
We are also deeply grateful to Weythman for several substantial contributions
|
|
to the code.
|
|
.\" .SG
|
|
.SH
|
|
References
|
|
.LP
|
|
.IP [1]
|
|
B. W. Kernighan and P. J. Plauger,
|
|
.ul
|
|
Software Tools,
|
|
Addison-Wesley, Inc., 1976.
|