From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/gnu_make/reference.html | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) create mode 100644 devdocs/gnu_make/reference.html (limited to 'devdocs/gnu_make/reference.html') diff --git a/devdocs/gnu_make/reference.html b/devdocs/gnu_make/reference.html new file mode 100644 index 00000000..8dfc3d86 --- /dev/null +++ b/devdocs/gnu_make/reference.html @@ -0,0 +1,16 @@ +

Basics of Variable References

To substitute a variable’s value, write a dollar sign followed by the name of the variable in parentheses or braces: either ‘$(foo)’ or ‘${foo}’ is a valid reference to the variable foo. This special significance of ‘$’ is why you must write ‘$$’ to have the effect of a single dollar sign in a file name or recipe.

Variable references can be used in any context: targets, prerequisites, recipes, most directives, and new variable values. Here is an example of a common case, where a variable holds the names of all the object files in a program: 

objects = program.o foo.o utils.o
+program : $(objects)
+        cc -o program $(objects)
+
+$(objects) : defs.h
+
+

Variable references work by strict textual substitution. Thus, the rule 

foo = c
+prog.o : prog.$(foo)
+        $(foo)$(foo) -$(foo) prog.$(foo)
+
+

could be used to compile a C program prog.c. Since spaces before the variable value are ignored in variable assignments, the value of foo is precisely ‘c’. (Don’t actually write your makefiles this way!)

A dollar sign followed by a character other than a dollar sign, open-parenthesis or open-brace treats that single character as the variable name. Thus, you could reference the variable x with ‘$x’. However, this practice can lead to confusion (e.g., ‘$foo’ refers to the variable f followed by the string oo) so we recommend using parentheses or braces around all variables, even single-letter variables, unless omitting them gives significant readability improvements. One place where readability is often improved is automatic variables (see Automatic Variables).

+

+ Copyright © 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022 Free Software Foundation, Inc.
Licensed under the GNU Free Documentation License.
+ https://www.gnu.org/software/make/manual/html_node/Reference.html +

+
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