GNU m4 1.4.16 宏处理器英文手册

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"GNU m4 1.4.16 是一个强大的宏处理器，它是 GNU 组织提供的一个软件包，实现了 m4 宏语言。这个手册是为版本 1.4.16 编写的，旨在指导用户如何使用和理解 m4 的功能。" GNU m4 是一个广泛应用的宏处理器，它允许用户定义和调用一系列预定义的文本模式，以进行复杂的文本处理任务。这个宏处理器在软件开发、脚本编写和文本自动化等领域都有广泛的应用。m4 的核心特性包括宏定义、字符串化、条件语句、循环结构以及对输入源文件的控制。 1. **简介与预备知识** - **1.1 引言**：介绍了 m4 的基本概念，包括它作为一个宏处理器的作用，以及它如何帮助用户通过宏扩展来处理文本。 - **1.2 历史参考**：概述了 m4 的历史背景和发展历程，可能包括它与其他宏处理器的关系，以及它如何演变为当前的版本。 - **1.3 问题与bug**：讨论了可能遇到的问题和已知的错误，用户可以参考这部分来解决使用过程中遇到的问题。 - **1.4 使用手册**：提供了如何有效地使用手册的指南，包括如何查找信息和解决疑问的方法。 2. **m4 的使用** - **2.1 操作模式的命令行选项**：这部分详细解释了如何通过命令行参数来改变 m4 的运行方式，例如设置不同的运行模式。 - **2.2 预处理器特性的命令行选项**：介绍了一些用于调整预处理行为的选项，如宏定义、引用处理等。 - **2.3 限制控制的命令行选项**：讲解了如何通过命令行参数来设置 m4 在处理文本时的各种限制，如内存大小、递归深度等。 - **2.4 冻结状态的命令行选项**：这些选项用于保存和恢复 m4 的状态，方便在不同阶段间进行操作。 - **2.5 调试选项**：描述了如何开启调试模式，以帮助开发者追踪和解决问题。手册还包含了 GNU Free Documentation License 的信息，允许用户自由地复制、分发和修改文档，这体现了 GNU 项目的开放源代码和共享精神。 3. **内容结构** 手册通常会进一步详细解释 m4 的语法、内置函数、自定义宏的创建方法，以及如何处理输入输出。它可能还会涵盖错误处理、宏扩展的例子，以及一些高级用法，如递归宏、条件编译等。 GNU m4 1.4.16 手册是一个全面的指南，对于想要掌握 m4 并利用其能力来处理复杂文本问题的用户来说，是一份宝贵的资源。通过深入学习，用户能够熟练运用 m4 来编写高效的脚本，自动化文本处理任务，或者作为其他软件开发过程中的工具。

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10 GNU M4 1.4.16 macro processor

goodbye

⇒

#line 12

⇒

goodbye

-U name

--undefine=name

This deletes any predeﬁned meaning name might have. Obviously, only prede-

ﬁned macros can be deleted in this way. This option may be given more than

once; undeﬁning a name that does not have a deﬁnition is silently ignored.

Order is signiﬁcant with respect to ﬁle names.

2.3 Command line options for limits control

There are some limits within m4 that can be tuned. For compatibility, m4 also accepts

some options that control limits in other implementations, but which are automatically

unbounded (limited only by your hardware and operating system constraints) in GNU m4.

-g

--gnu Enable all the extensions in this implementation. In this release of M4, this

option is always on by default; it is currently only useful when overriding a prior

use of ‘--traditional’. However, having GNU behavior as default makes it

impossible to write a strictly POSIX-compliant client that avoids all incompat-

ible GNU M4 extensions, since such a client would have to use the non-POSIX

command-line option to force full POSIX behavior. Thus, a future version of

M4 will be changed to implicitly use the option ‘--traditional’ if the envi-

ronment variable POSIXLY_CORRECT is set. Projects that intentionally use GNU

extensions should consider using ‘--gnu’ to state their intentions, so that the

project will not mysteriously break if the user upgrades to a newer M4 and has

POSIXLY_CORRECT set in their environment.

-G

--traditional

Suppress all the extensions made in this implementation, compared to the Sys-

tem V version. See Chapter 16 [Compatibility], page 109, for a list of these.

-H num

--hashsize=num

Make the internal hash table for symbol lookup be num entries big. For better

performance, the number should be prime, but this is not checked. The default

is 509 entries. It should not be necessary to increase this value, unless you

deﬁne an excessive number of macros.

-L num

--nesting-limit=num

Artiﬁcially limit the nesting of macro calls to num levels, stopping program

execution if this limit is ever exceeded. When not speciﬁed, nesting defaults

to unlimited on platforms that can detect stack overﬂow, and to 1024 levels

otherwise. A value of zero means unlimited; but then heavily nested code could

potentially cause a stack overﬂow.

Chapter 2: Invoking m4 11

The precise eﬀect of this option is more correctly associated with textual nesting

than dynamic recursion. It has been useful when some complex m4 input was

generated by mechanical means, and also in diagnosing recursive algorithms

that do not scale well. Most users never need to change this option from its

default.

This option does not have the ability to break endless rescanning loops, since

these do not necessarily consume much memory or stack space. Through clever

usage of rescanning loops, one can request complex, time-consuming computa-

tions from m4 with useful results. Putting limitations in this area would break

m4 power. There are many pathological cases: ‘define(‘a’, ‘a’)a’ is only the

simplest example (but see Chapter 16 [Compatibility], page 109). Expecting

GNU m4 to detect these would be a little like expecting a compiler system to

detect and diagnose endless loops: it is a quite hard problem in general, if not

undecidable!

-B num

-S num

-T num These options are present for compatibility with System V m4, but do nothing

in this implementation. They may disappear in future releases, and issue a

warning to that eﬀect.

-N num

--diversions=num

These options are present only for compatibility with previous versions of GNU

m4, and were controlling the number of possible diversions which could be used

at the same time. They do nothing, because there is no ﬁxed limit anymore.

They may disappear in future releases, and issue a warning to that eﬀect.

2.4 Command line options for frozen state

GNU m4 comes with a feature of freezing internal state (see Chapter 15 [Frozen ﬁles],

page 105). This can be used to speed up m4 execution when reusing a common initialization

script.

-F file

--freeze-state=file

Once execution is ﬁnished, write out the frozen state on the speciﬁed ﬁle. It is

conventional, but not required, for ﬁle to end in ‘.m4f’.

-R file

--reload-state=file

Before execution starts, recover the internal state from the speciﬁed frozen ﬁle.

The options ‘-D’, ‘-U’, and ‘-t’ take eﬀect after state is reloaded, but before

the input ﬁles are read.

2.5 Command line options for debugging

Finally, there are several options for aiding in debugging m4 scripts.

12 GNU M4 1.4.16 macro processor

-d[flags ]

--debug[=flags ]

Set the debug-level according to the ﬂags ﬂags. The debug-level controls the

format and amount of information presented by the debugging functions. See

Section 7.3 [Debug Levels], page 58, for more details on the format and meaning

of ﬂags. If omitted, ﬂags defaults to ‘aeq’.

--debugfile[=file ]

-o file

--error-output=file

Redirect dumpdef output, debug messages, and trace output to the named ﬁle.

Warnings, error messages, and errprint output are still printed to standard

error. If these options are not used, or if ﬁle is unspeciﬁed (only possible for

‘--debugfile’), debug output goes to standard error; if ﬁle is the empty string,

debug output is discarded. See Section 7.4 [Debug Output], page 60, for more

details. The option ‘--debugfile’ may be given more than once, and order is

signiﬁcant with respect to ﬁle names. The spellings ‘-o’ and ‘--error-output’

are misleading and inconsistent with other GNU tools; for now they are silently

accepted as synonyms of ‘--debugfile’ and only recognized once, but in a

future version of M4, using them will cause a warning to be issued.

-l num

--arglength=num

Restrict the size of the output generated by macro tracing to num characters

per trace line. If unspeciﬁed or zero, output is unlimited. See Section 7.3

[Debug Levels], page 58, for more details.

-t name

--trace=name

This enables tracing for the macro name, at any point where it is deﬁned. name

need not be deﬁned when this option is given. This option may be given more

than once, and order is signiﬁcant with respect to ﬁle names. See Section 7.2

[Trace], page 55, for more details.

2.6 Specifying input ﬁles on the command line

The remaining arguments on the command line are taken to be input ﬁle names. If no

names are present, standard input is read. A ﬁle name of ‘-’ is taken to mean standard

input. It is conventional, but not required, for input ﬁles to end in ‘.m4’.

The input ﬁles are read in the sequence given. Standard input can be read more than

once, so the ﬁle name ‘-’ may appear multiple times on the command line; this makes a

diﬀerence when input is from a terminal or other special ﬁle type. It is an error if an input

ﬁle ends in the middle of argument collection, a comment, or a quoted string.

The options ‘--define’ (‘-D’), ‘--undefine’ (‘-U’), ‘--synclines’ (‘-s’), and ‘--trace’

(‘-t’) only take eﬀect after processing input from any ﬁle names that occur earlier on the

command line. For example, assume the ﬁle ‘foo’ contains:

$ cat foo

bar

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