make file assignment

Lazy Set VARIABLE = value Normal setting of a variable, but any other variables mentioned with the value field are recursively expanded with their value at the point at which the variable is used, not the one it had when it was declared. Immediate Set VARIABLE := value Setting of a variable with simple expansion of the values inside - values within it are expanded at declaration time.

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 ...

Simple assignment :=. A simple assignment expression is evaluated only once, at the very first occurrence. For example, if CC :=${GCC} ${FLAGS} during the first encounter is evaluated to gcc -W then each time ${CC} occurs it will be replaced with gcc -W.. Recursive assignment =. A Recursive assignment expression is evaluated everytime the variable is encountered in the code.

Include another makefile. See Including Other Makefiles. override variable-assignment. Define a variable, overriding any previous definition, even one from the command line. See The override Directive. export. Tell make to export all variables to child processes by default. See Communicating Variables to a Sub-make. export variable export ...

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 .) Variables and functions in all parts of a makefile are ...

You can specify a value in the makefile, either with an assignment (see section Setting Variables) or with a verbatim definition (see section Defining Variables Verbatim). Variables in the environment become make variables. See section Variables from the Environment. Several automatic variables are given new values for each rule. Each of these ...

You can specify a value in the makefile, either with an assignment (see Setting Variables) or with a verbatim definition (see Defining Multi-Line Variables). Variables in the environment become make variables. See Variables from the Environment. Several automatic variables are given new values for each rule. Each of these has a single ...

Makefiles use a "line-based" syntax in which the newline character is special and marks the end of a statement. ... , to determine whether the line is a macro assignment or a rule (see Recipe Syntax). Internalize the resulting operation and read the next line. An important consequence of this is that a macro can expand to an entire rule, if ...

For each example, put the contents in a file called Makefile, and in that directory run the command make. Let's start with the simplest of Makefiles: hello: echo "Hello, World". Note: Makefiles must be indented using TABs and not spaces or make will fail. Here is the output of running the above example: $ make.

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.

The one-page guide to Makefile: usage, examples, links, snippets, and more.

suffices to perform all necessary recompilations. The make program uses the makefile data base and the last-modification times of the files to decide which of the files need to be updated. For each of those files, it issues the recipes recorded in the data base. You can provide command line arguments to make to control which files should be recompiled, or how.

An assignment of a variable on the command line overrides any value from the environment and any assignment in the makefile. Command-line assignments can set either simple or recursive variables by using := or =, respectively. It is possible using the override directive to allow a makefile assignment to be used instead of a command-line assignment.

You can specify a value in the makefile, either with an assignment (see section Setting Variables) or with a verbatim definition (see section Defining Variables Verbatim). Variables in the environment become make variables. See section Variables from the Environment. Several automatic variables are given new values for each rule. Each of these ...

Variables in a makefile work much the same as variables in a shell script. They are words to which a string of characters can be assigned. Once a string has been assigned to the variable, every reference to the variable in the rest of the makefile is replaced by the string. ... The variable is assigned a string value via an assignment statement ...

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 ...

You can specify a value in the makefile, either with an assignment (see section Setting Variables) or with a verbatim definition (see section Defining Variables Verbatim). Variables in the environment become make variables. See section Variables from the Environment. Several automatic variables are given new values for each rule. Each of these ...

3.7 How make Reads a Makefile. GNU make does its work in two distinct phases. During the first phase it reads all the makefiles, included makefiles, etc. and internalizes all the variables and their values and implicit and explicit rules, and builds a dependency graph of all the targets and their prerequisites. ... Variable Assignment. Variable ...

We say that expansion is immediate if it happens during the first phase: in this case make will expand any variables or functions in that section of a construct as the makefile is parsed. immediate := immediate. immediate += deferred or immediate. For the append operator, '+=', the right-hand side is considered immediate if the variable was ...

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 ...

This is not really equivalent to the code in the question. The wildcard substitution takes place while the Makefile is parsed, whereas for instance the shell commands can take place only once a Makefile rule is executed. This makes a difference when testing for existence of files generated by the Makefile. -

Conditional Assignment (GNU make) Previous: Immediately Expanded Variable Assignment , Up: The Two Flavors of Variables [ Contents ][ Index ] 6.2.4 Conditional Variable Assignment