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synced 2025-01-12 08:40:55 +00:00
* Removed Bourne shell $(a-b), etc. variable references.
* Fixed foreach documentation slightly. * Added chapter listing features tersely.
This commit is contained in:
Roland McGrath
parent
6b7b5698e9
commit
0bc6cc3735
1 changed files with 190 additions and 47 deletions
237
make.texinfo
237
make.texinfo
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@ -114,7 +114,11 @@ be recompiled, or how. @xref{Running}.
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* Implicit:: Implicit rules take over if the makefile doesn't say
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how a file is to be remade.
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* Archives:: How to use @code{make} to update archive files.
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* Missing:: Features of other @code{make}s not supported by GNU @code{make}.
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* Features:: GNU @code{make}'s advanced features and how GNU @code{make}
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relates to other versions of @code{make}.
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* Missing:: Features of other @code{make}s not supported
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by GNU @code{make}.
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* Concept Index::Index of cross-references to where concepts are discussed.
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* Name Index:: Index of cross-references for names of @code{make}'s
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@ -1900,12 +1904,10 @@ variables (@pxref{Automatic}).
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@subsection Modified References
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@cindex modified variable reference
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@cindex substitution variable reference
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@cindex conditional variable reference
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In addition to simple references, variables can be referenced in manners
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which modify the value of the reference but do not modify the value of
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the variable referenced. There are two categories of modified references:
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@dfn{substitution references} and @dfn{conditional references}.@refill
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In addition to simple references, variables can be referenced in a manner
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which modifies the value of the reference but do not modify the value of
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the variable referenced. Such a reference is a @dfn{substitution reference}.
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A @dfn{substitution reference} is really a simplified form of the
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@code{patsubst} expansion function (@pxref{Functions}). It has the form
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@ -1922,34 +1924,6 @@ bar := $(foo:.o=.c)
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@noindent
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sets @samp{bar} to @samp{a.c b.c c.c}. @xref{Setting}.
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@dfn{Conditional references} are references whose value depends on
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whether or not some variable is set. They are inspired by the similar
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construct in the shell @code{sh}. The syntax of conditional references is:
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@table @code
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@item $(@var{a}:-@var{b})
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This expands to the value of the variable @var{a} if it is defined or
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to @var{b} (a literal string) if it is not.
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@item $(@var{a}:+@var{b})
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This expands to @var{b} if the variable @var{a} is defined or to
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nothing (no characters) if it is not.
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@item $(@var{a}:@var{b}-@var{c})
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This expands to @var{b} if the variable @var{a} is defined or to
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@var{c} (a literal string) if it is not.
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@end table
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For the purpose of these conditional references, a variable is ``defined''
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if it exists and is non-null.
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In the first two alternatives, the @samp{:} may be omitted to produce
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a slightly different effect: then the variable @var{a} is considered
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``defined'' if it has been assigned any value, even a null value.
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Note that a variable value consisting solely of whitespace is @emph{not}
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null.
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@node Values, Flavors, Reference, Variables
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@section How Variables Get Their Values
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@ -1972,8 +1946,7 @@ Several @dfn{automatic} variables are given new values for each rule.
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@xref{Automatic}.
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@item
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Several variables have constant initial values. @xref{Implicit
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Variables}.
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Several variables have constant initial values. @xref{Implicit Variables}.
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@end itemize
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@node Flavors, Setting, Values, Variables
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@ -2008,12 +1981,12 @@ all:;echo $(foo)
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@end example
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@noindent
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will echo @samp{Huh?}: @code{$(foo)} expands to @code{$(bar)} which
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expands to @code{$(ugh)} which finally expands to @samp{Huh?}.@refill
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will echo @samp{Huh?}: @samp{$(foo)} expands to @samp{$(bar)} which
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expands to @samp{$(ugh)} which finally expands to @samp{Huh?}.@refill
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This flavor of variable is the only sort supported by other versions of
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@code{make}. It has its advantages and its disadvantages. An advantage
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(most would say) is that
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(most would say) is that:
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@example
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CFLAGS = $(include_dirs) -O
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@ -2030,8 +2003,8 @@ CFLAGS = $(CFLAGS) -O
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@end example
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@noindent
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because it will cause an infinite loop in the variable expansion. (Actually
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@code{make} detects the infinite loop and reports an error.)
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because it will cause an infinite loop in the variable expansion.
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(Actually @code{make} detects the infinite loop and reports an error.)
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Another disadvantage is that any functions (@pxref{Functions}) referenced
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in the definition will be executed every time the variable is expanded.
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@ -2698,8 +2671,9 @@ files := $(wildcard a/* b/* c/* d/*)
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The value of the variable @var{var} after the @code{foreach} function call
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is the same as the value beforehand. Other values taken from @var{list}
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are in effect only temporarily, during the execution of @code{foreach}.
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The variable @var{var} is the same flavor (recursively expanded or not)
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during @code{foreach} as it was before. @xref{Flavors}.
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The variable @var{var} is a simply-expanded variable during the execution
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of @code{foreach} but is returned to the same flavor it was before the
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@code{foreach} when it is done. @xref{Flavors}.
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If @var{var} was previously undefined, then it is defined as a recursively
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expanded variable (@samp{=}, not @samp{:=}) during the @code{foreach} and
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@ -3170,7 +3144,11 @@ On these occasions, you should use the @samp{-k} flag. This tells
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targets, remaking them if necessary, before it gives up and returns nonzero
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status. For example, after an error in compiling one object file,
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@samp{make -k} will continue compiling other object files even though it
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already knows that linking them will be impossible. @xref{Options}.
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already knows that linking them will be impossible. In addition to
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contuing after failing shell commands, @samp{make -k} will continue as much
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as possible after discovering that it doesn't know how to make a target or
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dependency file. This will always cause an error message, but without
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@samp{-k}, it is a fatal error. @xref{Options}.
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The usual behavior of @code{make} assumes that your purpose is to get the
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goals up to date; once @code{make} learns that this is impossible, it might
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@ -3189,7 +3167,8 @@ Here is a table of all the options @code{make} understands:
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@table @samp
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@item -b
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This option is ignored for compatibility with other versions of @code{make}.
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@itemx -m
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These options are ignored for compatibility with other versions of @code{make}.
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@item -c @var{dir}
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Change to directory @var{dir} before executing the rules. If multiple
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@ -4187,7 +4166,7 @@ The name of the first dependency that came via the implicit rule.
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For @code{.DEFAULT} commands, as for non-implicit commands, @samp{$*}
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and @samp{$<} are empty. @samp{$@@} is @var{t}, as always.
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@node Archives, Missing, Implicit, Top
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@node Archives, Features, Implicit, Top
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@chapter Using @code{make} to Update Archive Files
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@cindex archive
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@ -4293,7 +4272,171 @@ running @code{ranlib}. The rules for updating the members are not shown
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here; most likely you can omit them and use the implicit rule which copies
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files into the archive, as described in the preceding section.
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@node Missing, Concept Index, Archives, Top
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@node Features, Missing, Archive, Top
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@chapter Features of GNU @code{make}
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GNU @code{make} contains many features not in any other @code{make}
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program. Some of them are taken from other versions of @code{make}, while
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most are new inventions of the implementors of GNU @code{make}.
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The standard for comparison among versions of @code{make} in this chapter
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will be the version found in standard 4.2 BSD Unix systems. Many additions
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come from the versions of @code{make} found in other Unix systems. This
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chapter lists the features of GNU @code{make} beyond the 4.2 BSD version.
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They are presented as a simple list of small items with terse descriptions.
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All of these features (as well as those found in 4.2 BSD @code{make}) are
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documented in this manual, so it would be redundant to repeat that
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documentation here.
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The @code{VPATH} variable and its special meaning come from the @code{make}
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in 4.3 BSD Unix. @xref{Directory Search}.
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Many features come from the version of @code{make} in Sun Unix systems. I
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believe that these in turn are adopted from the @code{make} in Unix System V.
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@itemize @bullet
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@item
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Included makefiles. @xref{Include}.
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@item
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Variables are read in from the environment.
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All variables are placed into the environment of child processes (running
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commands). @xref{Environment}. Note also the @samp{-e} option.
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@item
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The environment variable @samp{MAKEFLAGS} is scanned for command-line
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options to @code{make}. The options @samp{-f}, @samp{-p}, @samp{-d} and
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@samp{-c} are not accepted. The @code{make} variable @samp{MAKEFLAGS} is
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set to a list of the options @code{make} was invoked with, except those
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noted above. @xref{Options/Recursion}.@refill
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@item
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The automatic variable @code{$%} is set to the member name
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in an archive reference. @xref{Automatic}.
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@item
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The automatic variables @code{$@@}, @code{$*}, @code{$<} and @code{$%} have
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corresponding forms such as @code{$(@@F)} and @code{$(@@D)} which with only
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the filename and only the directory. @xref{Automatic}.@refill
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@item
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Substitution variable references. @xref{Reference}.
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@item
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The command-line options @samp{-b} and @samp{-m} are accepted and ignored.
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@item
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Targets whose commands contain a reference to the variable @code{MAKE} have
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their commands executed even if the @samp{-n}, @samp{-q} or @samp{-t}
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options are specified. @xref{Recursion}. I'm told that Unix System V
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@code{make} does this only in the case of @samp{-n}.@refill
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@item
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An implicit suffix rule @samp{@var{x}.a:} makes
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@file{@var{lib}(@var{name}.o)} from @file{@var{name}.@var{x}}. In GNU
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@code{make}, this is actually implemented by using one pattern rule for
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making library-archive files and rule-chaining. @xref{Chaining}.@refill
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@end itemize
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The Sun Unix (and probably System V) version of @code{make} fails to
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support variable references using braces (@samp{@{} and @samp{@}}) rather
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than parantheses (@pxref{Reference}), and to set the @code{MFLAGS} variable
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to the list of options (the same list as in @code{MAKEFLAGS}).@refill
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The remaining new features are inventions new to GNU @code{make}.
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@itemize @bullet
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@item
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The arrangement of lines and backslash-newline combinations in
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commands is retained when the commands are printed, so they
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appear as they do in the makefile, except for the stripping of
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initial whitespace.
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This has been implemented in several versions of @code{make}.
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We're not sure who invented it first, but it's been spread around a bit.
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The @samp{-v} option prints version and copyright information.
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Rule chaining and implicit intermediate files.
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we got this from either of them or thought it up ourselves at the
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The automatic variable @code{$^} containing a list of all dependencies
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of the current target. @xref{Automatic}.
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@end itemize
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The variable @code{MAKEOVERRIDES} is defined to contain all
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the variable definitions given on the command line, and is
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appended to the @code{MAKE} variable which contains the name
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by which @code{make} was invoked. Thus, sub-makes will always
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get variable definitions from the command line that cannot
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come from the environment since environment variable
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definitions do not override those in makefiles.
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@itemize @bullet
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@item
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The @samp{-c} to change directory. @xref{Options}.
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@item
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Simply-expanded variables. @xref{Flavors}.
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@item
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Phony targets. @xref{Phony Targets}.
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@xref{Recursion}.
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Variable expansion functions. @xref{Functions}.
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The @samp{-c} command option to change directory. @xref{Options}.
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The @samp{-o} option makes files seem artificially old.
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@xref{Avoiding Recompilation}.
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@item
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Conditional lines. @xref{Conditionals}.
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A similar feature with a different syntax was implemented by
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Andrew Hume of AT&T Bell Labs in his @code{mk} program. This
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Included makefiles never determine the default target.
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@item
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There is an include file search path. @xref{Include}.
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@item
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@xref{MAKEFILES Variable}.
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@xref{Avoid Compilation}.
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@xref{Pattern Rules}.
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@code{make}; it seems a natural extension derived from the features
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of the C preprocessor and similar macro languages and is not a
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The automatic variable @code{$^} contains a list of all
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dependencies of the current target. @xref{Automatic}.
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@item
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Included makefiles never determine the default goal.
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There is a fully complete default set of implicit rules using
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file with suffixes @samp{.out}, @samp{.a}, @samp{.o},
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@samp{.s}, @samp{.c}, @samp{.f}, @samp{.p}, @samp{.F},
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@samp{.e}, @samp{.r}, @samp{.y}, @samp{.ye}, @samp{.yr} and
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@samp{.l}. @xref{Catalogue of Rules}.@refill
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@item
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Leading sequences of @samp{./} are stripped from file names,
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so that @file{./@var{file}} and @file{@var{file}} are
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considered to be the same file.
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@item
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Stripping leading sequences of @samp{./} from file names, so that
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Dependencies of the form @samp{-l@var{name}} are searched for
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as library archives. @xref{Library Search}.
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same file.
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Suffixes for suffix rules (@pxref{Suffix Rules}) may contain
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any characters. In other version of @code{make}, they must
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begin with @samp{.} and not contain any @samp{/} characters.
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@item
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The variable @code{MAKELEVEL} keeps track of the current level
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of @code{make} recursion. At the top level (@code{MAKELEVEL}
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is zero), the @code{SHELL} environment variable is not used to
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execute commands. It is reset to @samp{/bin/sh}.@refill
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@item
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Intermediate implicit files. @xref{Chained Rules}.
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Special search method for library dependencies written in the form
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@samp{-l@var{name}}. @xref{Libraries/Search}.
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@samp{.} and not contain any @samp{/} characters.
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@item
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The variable @code{MAKELEVEL} which keeps track of the current level
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of @code{make} recursion. @xref{Recursion}.
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The @code{make} programs in various other systems support three features
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