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01-introduction.md

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Introduction

Gaston Sanchez

Learning Objectives

  • Introduction to GNU Make
  • Understand: target, dependency, and rule concepts
  • Write simple makefile scripts
  • Makefile for markdown with pandoc

GNU Make

GNU Make, commonly known as make, is a Unix tool that is part of the GNU Project.

Make is a “tool which controls the generation of executables and other non-source files of a program from the program’s source files.”

To work with Make you write a text file with the name Makefile, typically referred to as the makefile.

A makefile is formed with rules that have the following structure:

target: dependencies ...
    commands
    ...

A rule tells Make how to execute a series of commands in order to build a target file from source files (i.e. the dependencies). Notice that the recipe line(s) must be indented with a TAB and not with any spaces.

Under its most basic form, a rule usually has this structure:

target: dependency
    command

For instance, let’s say you want to generate an html document output.html from a source markdown file input.md, generated with pandoc. The Make rule in this case would be:

# from markdown to html
output.html: input.md
    pandoc input.md -s -o output.html

  • the first line is a comment (comments are defined with #)

  • output.html is the target file

  • input.md is the dependency

  • pandoc input.md -s -o output.html is the command to build the target

You can have a directory make-test/ containing the source file input.md and the makefile Makefile:

make-test/
    input.md
    Makefile

Assuming that you are inside the directory make-test, in order to build the target file output.html, you simply call make from the command line:

make

The very first time you run make, you should be able to see in the command line the command that was executed:

pandoc input.md -s -o output.html

If everything went okay, you should be able to see the generated output file output.html.

Every time you make changes to the input file, you can run make again to build a new version of output.html.

Once output.html is built, if you run make again—without new changes made in input.md—Make will display a message like this one:

make: `output.html' is up to date.

This indicates that the timestamps of input.md and output.html are the same; which means there’s nothing new to be built. In other words, Make will do nothing if nothing needs to be done.

See the files in 01-minimal/ inside the examples/ folder to play with a minimal makefile.

Make documentation:

What a rule looks like