gnu make assignment operators

To set a variable from the makefile, write a line starting with the variable name followed by one of the assignment operators ' = ', ':= ', '::= ', or ':::= '. Whatever follows the operator and any initial whitespace on the line becomes the value. For example, objects = main.o foo.o bar.o utils.o. defines a variable named ...

973 Can anybody give a clear explanation of how variable assignment really works in Makefiles.

First, after assignment the variable is a normal recursive variable; when you append to it with ' += ' the value on the right-hand side is not expanded immediately. If you prefer the ' += ' operator to expand the right-hand side immediately you should use the ':= ' / '::= ' assignment instead. Second, these variables are ...

There is another assignment operator for variables, '?= '. This is called a conditional variable assignment operator, because it only has an effect if the variable is not yet defined.

Using Variables (GNU make) 6 How to Use Variables. A variable is a name defined in a makefile to represent a string of text, called the variable's value. These values are substituted by explicit request into targets, prerequisites, recipes, and other parts of the makefile. (In some other versions of make, variables are called macros.)

To make it dynamic, let's include the login username in the message so that the greeting is more personalized for each user. Let's define a user variable and initialize it with the output of the whoami command by using the assignment (=) operator: user= $(shell whoami) We should note that we followed a standard naming convention of using ...

GNU make - How to Use Variables. Go to the first, previous, next, last section, table of contents. How to Use Variables. A variable is a name defined in a makefile to represent a string of text, called the variable's value. These values are substituted by explicit request into targets, prerequisites, commands, and other parts of the makefile.

The GNU make manual seems to use the words variable and macro interchangeably. In this book, we'll use the word macro specifically to mean variables defined using the define directive and variable only when assignment is used. define create-jar. @echo Creating $@...

Simply expanded variables generally make complicated makefile programming more predictable because they work like variables in most programming languages. They allow you to redefine a variable using its own value (or its value processed in some way by one of the expansion functions) and to use the expansion functions much more efficiently (see ...

Makefile Variables Are Complicated - Makefile assignment tutorial. Since its appearance in 1976, Make has been helping developers automate complex processes for compiling code, building executables, and generating documentation. Like other programming languages, Make lets you define and use variables that facilitate reusability of values.

1. According to Gnu Make 6.5 Setting Variables: The shell assignment operator != can be used to execute a program and set a variable to its output. This operator first evaluates the right-hand side, then passes that result to the shell for execution.

With GNU Make, you can use := instead of = as in. TMP:=$(shell mktemp -d /tmp/.XXXXX) Edit As pointed out by Novelocrat, the = assignment differs from := assignment in that values assigned using = will be evaluated during substitution (and thus, each time, the variable is used), whereas := assigned variables will have their values evaluated ...

1 Overview of make. The make utility automatically determines which pieces of a large program need to be recompiled, and issues commands to recompile them. This manual describes GNU make, which was implemented by Richard Stallman and Roland McGrath.Development since Version 3.76 has been handled by Paul D. Smith. GNU make conforms to section 6.2 of IEEE Standard 1003.2-1992 (POSIX.2).

Functions allow you to do text processing in the makefile to compute the files to operate on or the commands to use in recipes. You use a function in a function call, where you give the name of the function and some text (the arguments) for the function to operate on. The result of the function's processing is substituted into the makefile at ...

gnu_make / latest / conditional-assignment.html. Conditional Variable Assignment. There is another assignment operator for variables, ...

The assignment operator is permitted in Gnu make 3.82, but not 3.81. What version of make are you using? - Eric Miller May 28, 2014 at 16:06

6.2.1 Recursively Expanded Variable Assignment. The first flavor of variable is a recursively expanded variable. Variables of this sort are defined by lines using ' = ' (see Setting Variables) or by the define directive (see Defining Multi-Line Variables). The value you specify is installed verbatim; if it contains references to other ...

Unfortunately, the shell assignment operator is not supported by the GNU Make shipped with macOS Monterey 12.6.1 and the output of the example is empty. It works in more recent versions of GNU Make though (e.g., 4.4), which are likely to be encountered in recent Linux distributions.

15 The != shell assignment operator is apparently supported on both BSD and GNU make:

6.2 The Two Flavors of Variables There are different ways that a variable in GNU make can get a value; we call them the flavors of variables. The flavors are distinguished in how they handle the values they are assigned in the makefile, and in how those values are managed when the variable is later used and expanded. Recursively Expanded Variable Assignment Simply Expanded Variable Assignment ...

1. run make -pn | less and you can see exactly what those variables are defined to. - user657267. Jan 27, 2017 at 10:41. 1. To be explicit about it, GNU make has a large catalog of built-in macros and predefined implicit rules. These are some of them.