GNU make manual 翻译( 一百二十八)

继续翻译

5.1 Recipe Syntax
=================

Makefiles have the unusual property that there are really two distinct
syntaxes in one file.  Most of the makefile uses `make' syntax (*note
Writing Makefiles: Makefiles.).  However, recipes are meant to be
interpreted by the shell and so they are written using shell syntax.
The `make' program does not try to understand shell syntax: it performs
only a very few specific translations on the content of the recipe
before handing it to the shell.

   Each line in the recipe must start with a tab (or the first character
in the value of the `.RECIPEPREFIX' variable; *note Special
Variables::), except that the first recipe line may be attached to the
target-and-prerequisites line with a semicolon in between.  _Any_ line
in the makefile that begins with a tab and appears in a "rule context"
(that is, after a rule has been started until another rule or variable
definition) will be considered part of a recipe for that rule.  Blank
lines and lines of just comments may appear among the recipe lines;
they are ignored.

   Some consequences of these rules include:

   * A blank line that begins with a tab is not blank: it's an empty
     recipe (*note Empty Recipes::).

   * A comment in a recipe is not a `make' comment; it will be passed
     to the shell as-is.  Whether the shell treats it as a comment or
     not depends on your shell.

   * A variable definition in a "rule context" which is indented by a
     tab as the first character on the line, will be considered part of
     a recipe, not a `make' variable definition, and passed to the
     shell.

   * A conditional expression (`ifdef', `ifeq', etc. *note Syntax of
     Conditionals: Conditional Syntax.) in a "rule context" which is
     indented by a tab as the first character on the line, will be
     considered part of a recipe and be passed to the shell.

5.1 片段语法
=================

makefile 有着罕有的属性，在一个文件中期时有两种独立的语法。多数的makefile 使用 make 语法(*note Writing Makefiles: Makefiles.) 但是，片段要被shell 所翻译，所以它们使用shell 的语法写成。make 程序并不试图去理解 shell 的语法：在把片段传递给shell 之前，它仅仅对几个特定内容进行翻译。

片段中的每一行都需要开始于一个 tab 键(或者第一个字符是 .RECIPEPREFIX 变量的值； *note Special Variables::)，除了第一行的片断行可以用一个分号连接在 目的-前提条件行之后。makefile中的任何开始于tab键的一行，并且出现在"规则上下文"(就是直到另一个规则或者变量定义出现之前)中的，将会被认为是那个规则的片段的一部分。空行和注释行可以出现在片段中，它们被忽略。

某些规则的推论如下:

*以tab 开始的空行不是真的空行：它是一个空片段(*note Empty Recipes::)

*片段中的注释不是 make 的注释；它会原样传递到shell中。shell 是否把它按照注释对待取决于你的shell。

*在一个 "规则上下文"中的 变量定义，如果是以tab键开头，将被认为是片段的部分，不会被认为是变量定义，会被传递到shell。

*一个条件性的表达式(ifdef, ifeq 等等 *note Syntax of Conditionals: Conditional Syntax) 在一个"规则上下文"中，如果有tab健开头，将会被认为是片段的一部分，将要被传递到shell。

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