@node Text Functions, Foreach Function, Function Syntax, Functions
@section Functions for String Substitution and Analysis
-Here are some functions that operate on substrings of a string:
+Here are some functions that operate strings:
@table @code
@item $(subst @var{from},@var{to},@var{text})
@var{pattern} may contain a @samp{%} which acts as a wildcard,
matching any number of any characters within a word. If
@var{replacement} also contains a @samp{%}, the @samp{%} is replaced
-by the text that matched the @samp{%} in @var{pattern}.
+by the text that matched the @samp{%} in @var{pattern}.@refill
Whitespace between words is folded into single space characters;
leading and trailing whitespace is discarded.
@findex sort
Sorts the words of @var{list} in lexical order, removing duplicate
words. The output is a list of words separated by single spaces.
+
+@item $(word @var{n},@var{text})
+@findex word
+Returns the @var{n}th word of @var{text}. If @var{n} is bigger than
+the number of words in @var{text}, nothing is returned. If you give
+0 as @var{n}, you will get a fatal error to remind you to quit
+thinking like a C programmer.
+
+@item $(words @var{text})
+@findex words
+Returns the number of words in @var{text}. Thus, @code{$(word
+$(words @var{text}),@var{text})} is the last word of @var{text}.@refill
@end table
Here is a realistic example of the use of @code{subst}. Suppose that a
@end example
@noindent
-produces the result @samp{foo}.
+produces the result @samp{foo}. Although @code{$(firstword
+@var{text})} is the same as @code{$(word 1,@var{text})}, the
+@code{firstword} function is retained for its ease of use.@refill
@item $(wildcard @var{pattern})
@findex wildcard
@node Features, Missing, Archives, Top
@chapter Features of GNU @code{make}
-GNU @code{make} contains many features not in any other @code{make}
-program. Some of them are taken from other versions of @code{make}, while
-most are new inventions of the implementors of GNU @code{make}.
-
-The standard for comparison among versions of @code{make} in this chapter
-will be the version found in standard 4.2 BSD Unix systems. Many additions
-come from the versions of @code{make} found in other Unix systems. This
-chapter lists the features of GNU @code{make} beyond the 4.2 BSD version.
-They are presented as a simple list of small items with terse descriptions.
-All of these features (as well as those found in 4.2 BSD @code{make}) are
-documented in this manual, so it would be redundant to repeat that
-documentation here.
+Here is a summary of the features of GNU @code{make}, for comparison
+with and credit to other versions of @code{make}. We consider the features
+of @code{make} in BSD 4.2 systems as a baseline.
The @code{VPATH} variable and its special meaning come from the @code{make}
-in 4.3 BSD Unix. @xref{Directory Search}.
+in BSD 4.3. @xref{Directory Search}.
-Many features come from the version of @code{make} in Sun Unix systems. I
-believe that these in turn are adopted from the @code{make} in Unix System V.
+Many features come from the version of @code{make} in System V:
@itemize @bullet
@item
Included makefiles. @xref{Include}.
@item
-Variables are read in from the environment.
-All variables are placed into the environment of child processes (running
-commands). @xref{Environment}. Note also the @samp{-e} option.
+Variables are read from and communicated via the environment.
+@xref{Environment}.
@item
-The environment variable @samp{MAKEFLAGS} is scanned for command-line
-options to @code{make}. The options @samp{-f}, @samp{-p}, @samp{-d} and
-@samp{-c} are not accepted. The @code{make} variable @samp{MAKEFLAGS} is
-set to a list of the options @code{make} was invoked with, except those
-noted above. @xref{Options/Recursion}.@refill
+Options passed through the variable @code{MAKEFLAGS} to recursive
+invocations of @code{make}. @xref{Options/Recursion}.
@item
The automatic variable @code{$%} is set to the member name
in an archive reference. @xref{Automatic}.
@item
-The automatic variables @code{$@@}, @code{$*}, @code{$<} and @code{$%} have
-corresponding forms such as @code{$(@@F)} and @code{$(@@D)} which are the
-simple form (such as @code{$@@}) with only the filename and only the
-directory, respectively. @xref{Automatic}.@refill
+The automatic variables @code{$@@}, @code{$*}, @code{$<} and @code{$%}
+have corresponding forms like @code{$(@@F)} and @code{$(@@D)}.
+@xref{Automatic}.@refill
@item
Substitution variable references. @xref{Reference}.
@item
-The command-line options @samp{-b} and @samp{-m} are accepted and ignored.
+The command-line options @samp{-b} and @samp{-m}, accepted and ignored.
@item
-Targets whose commands contain a reference to the variable @code{MAKE} have
-their commands executed even if the @samp{-n}, @samp{-q} or @samp{-t}
-options are specified. @xref{Recursion}. I'm told that Unix System V
-@code{make} does this only in the case of @samp{-n}.@refill
+Execution of recursive commands to run @code{make} via the variable
+@code{MAKE} even if @samp{-n}, @samp{-q} or @samp{-t} is specified.
+@xref{Recursion}.
@item
-An implicit suffix rule @samp{@var{x}.a:} makes
-@file{@var{lib}(@var{name}.o)} from @file{@var{name}.@var{x}}. In GNU
-@code{make}, this is actually implemented by using one pattern rule for
-making library-archive files and rule chaining. @xref{Chained Rules}.@refill
-@end itemize
+Support for suffix @samp{.a} in suffix rules. In GNU @code{make},
+this is actually implemented by chaining with one pattern rule for
+installing members in an archive. @xref{Chained Rules}.@refill
-The Sun Unix (and probably System V) version of @code{make} fails to
-support variable references using braces (@samp{@{} and @samp{@}}) rather
-than parantheses (@pxref{Reference}), and to set the @code{MFLAGS} variable
-to the list of options (the same list as in @code{MAKEFLAGS}).@refill
+@item
+The arrangement of lines and backslash-newline combinations in
+commands is retained when the commands are printed, so they appear as
+they do in the makefile, except for the stripping of initial
+whitespace.
+@end itemize
-The remaining features are inventions new to GNU @code{make}.
+Some features were inspired by a version of @code{make} whose identity we
+don't recall:
@itemize @bullet
@item
-The arrangement of lines and backslash-newline combinations in
-commands is retained when the commands are printed, so they
-appear as they do in the makefile, except for the stripping of
-initial whitespace.
+Pattern rules using @samp{%}.
This has been implemented in several versions of @code{make}.
We're not sure who invented it first, but it's been spread around a bit.
-The @samp{-v} option prints version and copyright information.
+@xref{Pattern Rules}.@refill
+
+@item
Rule chaining and implicit intermediate files.
+This was implemented by Stu Feldman in his version of @code{make}
+for AT&T Eighth Edition Research Unix, and later by Andrew Hume of
+AT&T Bell Labs in his @code{mk} program. We don't really know if
we got this from either of them or thought it up ourselves at the
+same time. @xref{Chained Rules}.
+
+@item
The automatic variable @code{$^} containing a list of all dependencies
of the current target. @xref{Automatic}.
@end itemize
-The variable @code{MAKEOVERRIDES} is defined to contain all
-the variable definitions given on the command line, and is
-appended to the @code{MAKE} variable which contains the name
-by which @code{make} was invoked. Thus, sub-makes will always
-get variable definitions from the command line that cannot
-come from the environment since environment variable
-definitions do not override those in makefiles.
+
+The remaining features are inventions new in GNU @code{make}:
+
@itemize @bullet
@item
-The @samp{-c} command option to change directories. @xref{Options}.
+The @samp{-v} option to print version and copyright information.
@item
Simply-expanded variables. @xref{Flavors}.
@item
-Phony targets with the special target @code{.PHONY}. @xref{Phony Targets}.
+Passing command-line variable assignments automatically through the
+variable @code{MAKE} to recursive @code{make} invocations.
@xref{Recursion}.
-Variable expansion functions. @xref{Functions}.
+@item
The @samp{-c} command option to change directory. @xref{Options}.
-The @samp{-o} option makes files seem artificially old.
+@item
Verbatim variable definitions made with @code{define}. @xref{Defining}.
@item
-Conditional lines. @xref{Conditionals}.
+Phony targets declared with the special target @code{.PHONY}.
A similar feature with a different syntax was implemented by
Andrew Hume of AT&T Bell Labs in his @code{mk} program. This
-Included makefiles never determine the default target.
+seems to be a case of parallel discovery. @xref{Phony Targets}.
@item
-There is an include file search path. @xref{Include}.
+Text manipulation by calling functions. @xref{Functions}.
@item
-@xref{MAKEFILES Variable}.
+The @samp{-o} option to pretend a file's modification-time is old.
@xref{Avoid Compilation}.
-@xref{Pattern Rules}.
+@item
+Conditional execution.
+This has been implemented numerous times in various versions of
@code{make}; it seems a natural extension derived from the features
of the C preprocessor and similar macro languages and is not a
-The automatic variable @code{$^} contains a list of all
-dependencies of the current target. @xref{Automatic}.
+revolutionary concept. @xref{Conditionals}.
+
@item
Included makefiles never determine the default goal.
-There is a complete default set of implicit rules to operate on libraries,
-assembler, C, Fortran, Pascal, EFL, Ratfor, Yacc, and Lex sources and RCS
-and SCCS files. @xref{Catalogue of Rules}.
@item
-Leading sequences of @samp{./} are stripped from file names, so that
-@file{./@var{file}} and @file{@var{file}} are considered to be the same file.
-@item
-Stripping leading sequences of @samp{./} from file names, so that
-Dependencies of the form @samp{-l@var{name}} are searched for
-as library archives. @xref{Libraries/Search}.
-same file.
-
-Suffixes for suffix rules (@pxref{Suffix Rules}) may contain
-any characters. In other version of @code{make}, they must
-begin with @samp{.} and not contain any @samp{/} characters.
+The included makefile search path. @xref{Include}.
@item
-The variable @code{MAKELEVEL} keeps track of the current level
-of @code{make} recursion. At the top level (@code{MAKELEVEL}
-is zero), the @code{SHELL} environment variable is not used to
-execute commands. It is reset to @samp{/bin/sh}.@refill
+Specifying extra makefiles to read. @xref{MAKEFILES Variable}.
@item
-Intermediate implicit files. @xref{Chained Rules}.
+Stripping leading sequences of @samp{./} from file names, so that
+@file{./@var{file}} and @file{@var{file}} are considered to be the
+same file.
-@item
@item
Special search method for library dependencies written in the form
@samp{-l@var{name}}. @xref{Libraries/Search}.
suffix rule @samp{.c~.o} would make the file @file{@var{n}.o} file from
the SCCS file @file{s.@var{n}.c}. For complete coverage, a whole
series of such suffix rules is required. @xref{Suffix Rules}.@refill
-rules. The System V @code{make} rule:
+
In GNU @code{make}, this entire series of cases is handled by two
pattern rules for extraction from SCCS, in combination with the
general feature of rule chaining. @xref{Chained Rules}.
projects / thirdparty / make.git / commitdiff
