Editing Make (software) (section)

===Macros===

A makefile can define and use macros. Macros are usually referred to as ''variables'' when they hold simple string definitions, like {{code|1=CC=clang|lang=make}}. Macros in makefiles may be overridden in the [[command-line argument]]s passed to the Make utility. [[Environment variables]] are also available as macros.

For example, the macro {{code|CC}} is frequently used in makefiles to refer to the location of a [[C (programming language)|C]] compiler. If used consistently throughout the makefile, then the compiler used can be changed by changing the value of the macro rather than changing each rule command that invokes the compiler.

Macros are commonly named in [[all-caps]]:

<syntaxhighlight lang="make">
MACRO = definition
</syntaxhighlight>

A macro value can consist of other macro values. The value of macro is expanded on each use [[lazy evaluation|lazily]].

A macro is used by expanding either via $''NAME'' or $(''NAME''). The latter is safer since omitting the parentheses leads to Make interpreting the next letter after the {{code|$}} as the entire variable name. An equivalent form uses curly braces rather than parentheses, i.e. {{code|${} }}, which is the style used in [[BSD]].

<syntaxhighlight lang="make">
NEW_MACRO = $(MACRO)-$(MACRO2)
</syntaxhighlight>

Macros can be composed of shell commands by using the [[command substitution]] operator <code>!=</code>.<ref>{{Cite web |url=https://pubs.opengroup.org/onlinepubs/9799919799/utilities/make.html |title=Make |access-date=2024-10-29 |archive-date=2024-10-05 |archive-url=https://web.archive.org/web/20241005234028/https://pubs.opengroup.org/onlinepubs/9799919799/utilities/make.html |url-status=live }}</ref>

<syntaxhighlight lang="make">
YYYYMMDD != date
</syntaxhighlight>

The command-line syntax for overriding a macro is:

<syntaxhighlight lang="bash">
make MACRO="value" [MACRO="value" ...] TARGET [TARGET ...]
</syntaxhighlight>

Makefiles can access predefined ''internal macros'', with {{code|?}} and {{code|@}} being common.

<syntaxhighlight lang="make">
target: component1 component2
	# echo components YOUNGER than TARGET
	echo $? 
	# echo TARGET name
	echo $@ 
</syntaxhighlight>

A common syntax when defining macros, which works on BSD and GNU Make, is to use {{mono|1=+=}}, {{mono|1=?=}}, and {{mono|1=!=}} instead of the equal sign ({{mono|1==}}).<ref>{{man|1|make|FreeBSD}}</ref>