diff options
Diffstat (limited to 'doc/make.texi')
| -rw-r--r-- | doc/make.texi | 77 |
1 files changed, 46 insertions, 31 deletions
diff --git a/doc/make.texi b/doc/make.texi index 9b8faee..d723d2d 100644 --- a/doc/make.texi +++ b/doc/make.texi @@ -1399,6 +1399,7 @@ Variable definitions are parsed as follows: @var{immediate} = @var{deferred} @var{immediate} ?= @var{deferred} @var{immediate} := @var{immediate} +@var{immediate} ::= @var{immediate} @var{immediate} += @var{deferred} or @var{immediate} @var{immediate} != @var{immediate} @@ -1418,6 +1419,10 @@ define @var{immediate} := @var{immediate} endef +define @var{immediate} ::= + @var{immediate} +endef + define @var{immediate} += @var{deferred} or @var{immediate} endef @@ -1429,7 +1434,7 @@ endef For the append operator, @samp{+=}, the right-hand side is considered immediate if the variable was previously set as a simple variable -(@samp{:=}), and deferred otherwise. +(@samp{:=} or @samp{::=}), and deferred otherwise. For the shell assignment operator, @samp{!=}, the right-hand side is evaluated immediately and handed to the shell. The result is stored in the @@ -4967,9 +4972,9 @@ all:;echo $(foo) will echo @samp{Huh?}: @samp{$(foo)} expands to @samp{$(bar)} which expands to @samp{$(ugh)} which finally expands to @samp{Huh?}.@refill -This flavor of variable is the only sort supported by other versions of -@code{make}. It has its advantages and its disadvantages. An advantage -(most would say) is that: +This flavor of variable is the only sort supported by most other +versions of @code{make}. It has its advantages and its disadvantages. +An advantage (most would say) is that: @example CFLAGS = $(include_dirs) -O @@ -5005,8 +5010,14 @@ variables, there is another flavor: simply expanded variables. @cindex simply expanded variables @cindex variables, simply expanded @cindex := +@cindex ::= @dfn{Simply expanded variables} are defined by lines using @samp{:=} -(@pxref{Setting, ,Setting Variables}). +or @samp{::=} (@pxref{Setting, ,Setting Variables}). Both forms are +equivalent in GNU @code{make}; however only the @samp{::=} form is +described by the POSIX standard (support for @samp{::=} was added to +the POSIX standard in 2012, so older versions of @code{make} won't +accept this form either). + The value of a simply expanded variable is scanned once and for all, expanding any references to other variables and functions, when the variable is defined. The actual value of the simply @@ -5425,12 +5436,14 @@ Several variables have constant initial values. @cindex variables, setting @cindex = @cindex := +@cindex ::= @cindex ?= @cindex != To set a variable from the makefile, write a line starting with the -variable name followed by @samp{=} or @samp{:=}. Whatever follows the -@samp{=} or @samp{:=} on the line becomes the value. For example, +variable name followed by @samp{=} @samp{:=}, or @samp{::=}. Whatever +follows the @samp{=}, @samp{:=}, or @samp{::=} on the line becomes the +value. For example, @example objects = main.o foo.o bar.o utils.o @@ -5440,10 +5453,11 @@ objects = main.o foo.o bar.o utils.o defines a variable named @code{objects}. Whitespace around the variable name and immediately after the @samp{=} is ignored. -Variables defined with @samp{=} are @dfn{recursively expanded} variables. -Variables defined with @samp{:=} are @dfn{simply expanded} variables; these -definitions can contain variable references which will be expanded before -the definition is made. @xref{Flavors, ,The Two Flavors of Variables}. +Variables defined with @samp{=} are @dfn{recursively expanded} +variables. Variables defined with @samp{:=} or @samp{::=} are +@dfn{simply expanded} variables; these definitions can contain +variable references which will be expanded before the definition is +made. @xref{Flavors, ,The Two Flavors of Variables}. The variable name may contain function and variable references, which are expanded when the line is read to find the actual variable name to use. @@ -5553,12 +5567,12 @@ explanation of the two flavors of variables. When you add to a variable's value with @samp{+=}, @code{make} acts essentially as if you had included the extra text in the initial -definition of the variable. If you defined it first with @samp{:=}, -making it a simply-expanded variable, @samp{+=} adds to that -simply-expanded definition, and expands the new text before appending it -to the old value just as @samp{:=} does -(see @ref{Setting, ,Setting Variables}, for a full explanation of @samp{:=}). -In fact, +definition of the variable. If you defined it first with @samp{:=} or +@samp{::=}, making it a simply-expanded variable, @samp{+=} adds to +that simply-expanded definition, and expands the new text before +appending it to the old value just as @samp{:=} does (see +@ref{Setting, ,Setting Variables}, for a full explanation of +@samp{:=} or @samp{::=}). In fact, @example variable := value @@ -5898,13 +5912,13 @@ Multiple @var{target} values create a target-specific variable value for each member of the target list individually. The @var{variable-assignment} can be any valid form of assignment; -recursive (@samp{=}), simple (@samp{:=}), appending (@samp{+=}), or -conditional (@samp{?=}). All variables that appear within the -@var{variable-assignment} are evaluated within the context of the -target: thus, any previously-defined target-specific variable values -will be in effect. Note that this variable is actually distinct from -any ``global'' value: the two variables do not have to have the same -flavor (recursive vs.@: simple). +recursive (@samp{=}), simple (@samp{:=} or @samp{::=}), appending +(@samp{+=}), or conditional (@samp{?=}). All variables that appear +within the @var{variable-assignment} are evaluated within the context +of the target: thus, any previously-defined target-specific variable +values will be in effect. Note that this variable is actually +distinct from any ``global'' value: the two variables do not have to +have the same flavor (recursive vs.@: simple). Target-specific variables have the same priority as any other makefile variable. Variables provided on the command line (and in the @@ -8463,10 +8477,10 @@ makefile works by changing the variables. When you override a variable with a command line argument, you can define either a recursively-expanded variable or a simply-expanded variable. The examples shown above make a recursively-expanded -variable; to make a simply-expanded variable, write @samp{:=} instead -of @samp{=}. But, unless you want to include a variable reference or -function call in the @emph{value} that you specify, it makes no -difference which kind of variable you create. +variable; to make a simply-expanded variable, write @samp{:=} or +@samp{::=} instead of @samp{=}. But, unless you want to include a +variable reference or function call in the @emph{value} that you +specify, it makes no difference which kind of variable you create. There is one way that the makefile can change a variable that you have overridden. This is to use the @code{override} directive, which is a line @@ -11024,6 +11038,7 @@ Here is a summary of the directives GNU @code{make} recognizes: @item define @var{variable} @itemx define @var{variable} = @itemx define @var{variable} := +@itemx define @var{variable} ::= @itemx define @var{variable} += @itemx define @var{variable} ?= @itemx endef @@ -11479,9 +11494,9 @@ prerequisites, etc., one of them depended on @var{xxx} again. @item Recursive variable `@var{xxx}' references itself (eventually). Stop. This means you've defined a normal (recursive) @code{make} variable @var{xxx} that, when it's expanded, will refer to itself (@var{xxx}). -This is not allowed; either use simply-expanded variables (@code{:=}) or -use the append operator (@code{+=}). @xref{Using Variables, ,How to Use -Variables}. +This is not allowed; either use simply-expanded variables (@samp{:=} +or @samp{::=}) or use the append operator (@samp{+=}). @xref{Using +Variables, ,How to Use Variables}. @item Unterminated variable reference. Stop. This means you forgot to provide the proper closing parenthesis |