转义换行符是否属于POSIX make标准？合规性及术语含义求解

Great question—let’s break this down clearly, starting with the "historical convention" you’re curious about.

What does "historical convention" refer to here? #

This phrase points to a syntax behavior that grew out of early Unix make implementations, long before POSIX formalized standards for make. Back in the day, developers needed a way to split long, unwieldy lines in Makefiles into more readable chunks without breaking the logical structure of rules or variable definitions.

The practice of using a backslash \ immediately followed by a newline to "merge" multiple physical lines into one logical line became a de facto standard across different make tools. It wasn’t a written rule at first—it was just how people used make, and over time it became an expected feature that stuck around.

Your examples perfectly illustrate this:

• The rule .c.o\ : is treated exactly like .c.o: because the escaped newline tells make to ignore the line break and treat the two lines as a single logical rule definition.
• The variable definition f= bar baz\ biz merges the two physical lines into one variable value: bar baz biz, which is why the echo outputs ==bar baz biz==.

Can escaped newlines be used in strictly compliant POSIX Makefiles? #

Absolutely—POSIX has officially codified this historical convention into its standard. As long as you follow the exact syntax requirement (the backslash must be the last character on the line, with no spaces or other characters after it before the newline), using escaped newlines is fully compliant with POSIX make specifications.

This means you can safely use escaped newlines in any POSIX-compliant make environment to split long variable definitions, rule lines, or command sequences into more manageable, readable lines without breaking functionality.

内容的提问来源于stack exchange，提问作者MarkWeston