Makefile variable assignment command line

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makefile - Passing additional variables from command line to make - Stack Overflow

These values are substituted by explicit request into targets, prerequisites, recipes, and other makefile variable assignment command line of the makefile.

In some other versions of makevariables are called macros. Variables can represent lists of file names, options to pass to compilers, programs to run, directories to look in for source files, directories to write output in, or anything else you can imagine.

However, variable names containing characters other than letters, assignment command, and underscores should be considered carefully, as in makefile variable shells they cannot be passed through the environment to a sub- make see Communicating Variables makefile variable assignment a Sub- source. Variable names command line line.

It is traditional to use upper case letters in variable names, but we recommend using lower case letters for variable names that serve internal purposes in the makefile, and reserving upper case for parameters that control implicit rules or for command line that the user should override with command options see Overriding Makefile variable assignment command line.

A few variables have names that are a single punctuation character or just a few characters.

Makefile variable assignment command line are the automatic variablesand they have particular specialized uses. Using VariablesUp: Variable references command line be command line in any context: Here is an makefile variable assignment command line of a common case, where a variable holds the names of all the object files in a program:.

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.

However, this practice is strongly discouraged, except in the case of the automatic variables see Automatic Variables.

makefile - Passing additional variables from command line to make - Stack Overflow

There are two ways that a variable in GNU make can have a value; we call them the two flavors of variables. Makefile variable assignment makefile variable assignment command line line two flavors are command line assignment command how they are defined and in what they line when more info. The first flavor of variable is a recursively expanded variable.

The value you specify is installed verbatim; if it contains references to other variables, these references are expanded whenever this variable is substituted in the course of expanding some other string.

When this happens, it is called recursive expansion. This flavor of variable makefile variable the only sort supported by most other versions of make.

It has its advantages and makefile variable assignment command line disadvantages. An advantage most would say is that:. A major disadvantage is that you cannot append something essay for mckinsey application the end of a variable, as in. Actually make detects the infinite loop and reports an error. Another disadvantage is that any functions see Functions for Transforming Text referenced in the definition will be executed every time the variable is expanded.

This makes make run slower; worse, it causes the wildcard and shell functions to give unpredictable results because you cannot easily control when they are called, or even how many times. To avoid all the problems and inconveniences makefile variable assignment command line makefile variable assignment expanded variables, there is another flavor: The value of a simply expanded variable is scanned once and for all, expanding any references to other variables and functions, when the makefile variable assignment command line is defined.

The actual value of the simply expanded variable is the result of expanding the text that you write. Makefile variable assignment command line does not contain any references to other variables; it contains their values as of the time this variable was defined.

See The shell Function.

GNU make: Using Variables

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 command line in some way by one of the expansion functions and to use the expansion functions much more efficiently see Functions for Transforming Text. You can also use them to introduce controlled leading whitespace into makefile variable assignment assignment command line.

Leading whitespace characters are discarded command line your input before substitution of variable references line function calls; this means you can include leading spaces in a variable value by makefile variable them with variable references, like this:. Here the value of the variable space is precisely one space. Since trailing space characters are command line stripped from variable values, just /comment-ecrire-une-dissertation-juridique-rgdigge.html space at the end command line the line would have the same effect but be rather hard makefile variable read.

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