15 Make

Mauro Jaskelioff(Originally by Gail Hopkins)

Introduction

• Use of makefiles to manage the build process

• Declarative, imperative and relational rules

• Environment variables, phony targets, automatic variables, macros and pattern matching in makefiles

• Creating recursive makefiles

Build Management

• During the implementation phase, the process for constructing a system should be engineered– What are the steps needed to build the

system?– Who is authorised to build a system?

• Individual programmers, build/configuration managers

– When are system builds performed?

Build Management and Tools

• Most modern programming environments have build management capabilities built into them– E.g. a Java development environment

typically has the notion of a “project” and it can compile all project files in the correct order (and it only compiles files dependent on a change)

UNIX Build Management

• In UNIX environments, a common management tool is “make”

• Make uses three specification styles– Declarative– Imperative– Relational

• These styles are combined into “the makefile”

Specification Styles

• Operational or Imperative– Describes the actions to be taken

• Descriptive or Declarative– Describes the desired properties

• Structural or Relational– Describes relationships between things

The Make Specification Language

• Dependencies between things (modules, files, etc.) are relational

• Rules for creating new things are declarative

• The Actions needed to carry out the rules are imperative

Make Command Line$ make

• Make will look for a file called makefile or Makefile

• Make looks inside the file for a target– A target can be a file to be generated (but not

necessarily!)

• Different targets can be specified - frequently all and clean - and called as make all. If no target specified (i.e. just make is called) then it picks the first in the file

A Typical Make Rule

T1 is the target T2 and T3 are dependencies - T1 depends

on T2 and T3. These are other targets in the file

A1 and A2 are actions written as a tab followed by a list of UNIX (shell) commands

T1: T2 T3A1A2

Example Makefile

javac calls a UNIX Java compiler.• java runs a UNIX Java program.• jar archives a set of Java classes in

one JAR file.

Targets

Actionmain1.class: main1.java

javac main1.java

Example Makefile

main1.class: mysubroutines.jar main1.javajavac main1.java

mysubroutines.class: mysubroutines.javajavac mysubroutines.java

mysubroutines.jar: mysubroutines.classjar cvf mysubroutines.jar mysubroutines.class

More on Rules

target: dependencies actions

• Target and dependencies are generally files.

• If any dependency is modified more recently than its target then make performs the associated actions.

More on Rules (2)

• An action can be any shell command, one per line. Each action must begin with a tab. All variables used in actions must have ( ) brackets round them – e.g. $(PATH).

• Typically, actions create the target file from the dependency files.

• GOTCHA: Watch out for actions that do not actually create their target.

More on Actions

• Actions do not have to invoke a compiler

• Targets do not have to be files• Targets, like clean and all which do

not create files are called phony targets

Example Makefile

all: main1.class

main1.class: mysubroutines.jar main1.javajavac main1.java

mysubroutines.class: mysubroutines.javajavac mysubroutines.java

mysubroutines.jar: mysubroutines.classjar cvf mysubroutines.jar mysubroutines.class

• NOTE: Remember this will remove files!

clean:rm *.classrm *.jar

More on Phony Targets• Phony targets are useful for

deployment

• If I type make install, make checks to see if the file program in the current directory is newer than the one in my bin directory. If it is, it copies (or installs) the new version.

install: /home/domain/zlizmj/bin/program

/home/domain/zlizmj/bin/program: programcp program /home/domain/zlizmj/bin/program

Another Makefile

all: main1.class

main1.class: mysubroutines.jar main1.javajavac main1.java

install: /home/domain/zlizmj/bin/main1.class

/home/domain/zlizmj/bin/main1.class: main1.classcp main1.class /home/domain/zlizmj/bin/main1.class

Using Environment Variables

• Installing in bin isn’t much use if you don’t know where it is!

• Make has variable-like objects known as macros.

• Environment variables, like $HOME and $PATH can be detected by make.

INSTALLDIR = $(HOME)/bininstall: $(INSTALLDIR)/program

$(INSTALLDIR)/program: programcp program $(HOME)/bin/program

Another Makefile

INSTALLDIR = $(HOME)/binall: main1.classmain1.class: mysubroutines.jar main1.java

javac main1.java

install: $(INSTALLDIR)/main1.class

$(INSTALLDIR)/main1.class: main1.classcp main1.class $(INSTALLDIR)/main1.class

Make Macros

• A Macro holds a string value• This string is defined using an equal

sign and preceded by a dollar sign.• Without the brackets make assumes

that the name is just one letter long: $INSTALLDIR is interpreted as $(I)NSTALLDIR

Macro Substitution

• Make performs strict textual replacement to work out what variables are, so the following two rules are equivalent:

program: output.og++ output.o -o program

FOO = opr$(FOO)gram: $(FOO)utput.$(FOO)

g++ $(FOO)utput.$(FOO) -$(FOO) pr$(FOO)gram

Increased Abstraction• Macros increase the level of abstraction

in a Makefilemysubroutines.jar: mysubroutines.class main2.classjar cvf mysubroutines.class main2.class

• is equivalent to

JARFILE = mysubroutines.jarOBJECTS = mysubroutines.class main2.class$(JARFILE): $(OBJECTS)jar cvf $(OBJECTS)

Automatic Variables

• Make has a special feature called automatic variables

• Automatic variables can only be used within the actions of a make rule – its value depends on the target and dependencies of the rule.

Automatic Variables (2)

• $@ – The target of the rule

• $< – The first dependency

• $ˆ – All the dependencies

• $? – All of the dependencies that are newer than the

target.

• $* – The stem of a pattern matching rule

Example of Automatic Variable Use

mysubroutines.jar: mysubroutines.classjar mysubroutines.jar mysubroutines.class

mysubroutines.jar: mysubroutines.classjar $@ $<

mysubs.jar: mysubroutines.class myutil.classjar mysubs.jar mysubroutines.class myutil.class

mysubs.jar: mysubroutines.class myutil.classjar $@ $ˆ

Pattern Matching

• NOTE: These are not present in all versions of Make – but are on unnc-cslinux and most Linux based versions.

• Suppose you have a lot of classes in a directory and you want to compile them individually.

• You could have a rule for each class

Pattern Matching (2)

• Or you could use a pattern:

exercise1.class: exercise1.javajavac exercise1.java

exercise2.class: exercise2.javajavac exercise2.java

%.class: %.javajavac $<

Example Makefile

INSTALLDIR = $(HOME)/bin

all: main1.class

install: $(INSTALLDIR)/main1.class

$(INSTALLDIR)/main1.class: main1.classcp main1.class $(INSTALLDIR)/main1.class

%.class: %.javajavac $<

clean:rm *.classrm *.jar

Benefits of Pattern Matching

• Scalability – The same rule can apply to thousands

(or more) files.• Compactness

– Small compact specifications are easier to understand and debug.

• These are similar to the benefits of using wild-cards and regular expressions.

Managing More Complex Projects with Make

• Many large projects will contain a lot of subprograms, the code will be spread over several directories and all will have to be compiled to get the final system to work.– You can manage this using several

Makefiles if you chose.– Use cd in the Actions to enter a

subdirectory and then you can call a makefile there.

Example of a Recursive Makefile

all:

cd interface; makecd program1; makecd program2; make

clean

cd interface; make cleancd program1; make cleancd program2; make clean

Summary

• Using a tool, like make, for installation can make your life easier. It saves remembering dependencies, and typing compiler flags etc.

• It will also make life easier for anyone else who wants to use your code. They only have to type make.

• Typically all distributions contain a README (or possibly install.txt) which should tell you what to do, in particular if the Makefile needs to be edited.