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12 GNU make

3.1.1 Splitting Long Lines

Makeﬁles use a “line-based” syntax in which the newline character is special and marks the

end of a statement. GNU make has no limit on the length of a statement line, up to the

amount of memory in your computer.

However, it is diﬃcult to read lines which are too long to display without wrapping or

scrolling. So, you can format your makeﬁles for readability by adding newlines into the

middle of a statement: you do this by escaping the internal newlines with a backslash (\)

character. Where we need to make a distinction we will refer to “physical lines” as a single

line ending with a newline (regardless of whether it is escaped) and a “logical line” being a

complete statement including all escaped newlines up to the ﬁrst non-escaped newline.

The way in which backslash/newline combinations are handled depends on whether the

statement is a recipe line or a non-recipe line. Handling of backslash/newline in a recipe

line is discussed later (see Section 5.1.1 [Splitting Recipe Lines], page 41).

Outside of recipe lines, backslash/newlines are converted into a single space character.

Once that is done, all whitespace around the backslash/newline is condensed into a single

space: this includes all whitespace preceding the backslash, all whitespace at the beginning

of the line after the backslash/newline, and any consecutive backslash/newline combina-

tions.

If the .POSIX special target is deﬁned then backslash/newline handling is modiﬁed

slightly to conform to POSIX.2: ﬁrst, whitespace preceding a backslash is not removed

and second, consecutive backslash/newlines are not condensed.

3.2 What Name to Give Your Makeﬁle

By default, when make looks for the makeﬁle, it tries the following names, in order:

GNUmakefile, makefile and Makefile.

Normally you should call your makeﬁle either makefile or Makefile. (We recommend

Makefile because it appears prominently near the beginning of a directory listing, right

near other important ﬁles such as README.) The ﬁrst name checked, GNUmakefile, is not

recommended for most makeﬁles. You should use this name if you have a makeﬁle that is

speciﬁc to GNU make, and will not be understood by other versions of make. Other make

programs look for makefile and Makefile, but not GNUmakefile.

If make ﬁnds none of these names, it does not use any makeﬁle. Then you must specify

a goal with a command argument, and make will attempt to ﬁgure out how to remake it

using only its built-in implicit rules. See Chapter 10 [Using Implicit Rules], page 111.

If you want to use a nonstandard name for your makeﬁle, you can specify the makeﬁle

name with the ‘-f’ or ‘--file’ option. The arguments ‘-f name’ or ‘--file=name’ tell

make to read the ﬁle name as the makeﬁle. If you use more than one ‘-f’ or ‘--file’

option, you can specify several makeﬁles. All the makeﬁles are eﬀectively concatenated in

the order speciﬁed. The default makeﬁle names GNUmakefile, makefile and Makefile are

not checked automatically if you specify ‘-f’ or ‘--file’.

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