By Heike Jurzik
Anyone who has compiled a program from the source code will be familiar with the make tool, the central part of the configure, make, make install three-card trick for building and installing software on Linux. This is not the only situation in which make provides useful service. Make can also assist with other tasks, for example, in larger projects, LaTeX users can use make to automatically recompile and create a Postscript or PDF document if one or multiple source files have changed.
Make also helps sysadmins, and it can automatically launch a backup script if you have modified one or more files. A control file, makefile, describes the chores you want make to handle. After setting up the makefile, you can simply call make - and let it do all the work.
The make program is available for a variety of platforms. In this article, we will be looking at GNU make, which is used in the Linux world. I'll investigate the makefile layout and introduce the command's most interesting options.
The makefile is the control point for working with make. Each makefile holds a list of instructions. Make expects a GNUmakefile, makefile, or Makefile, and it looks for the control file in this order in the current directory. The makefile contains rules that follow this syntax:
Target: Dependency (ies)
command
command
...
The target refers to the expected result of the commands that follow. The colon is followed by one or multiple files required to build the target, that is, on which the target depends. This list is followed by the actions that make will perform, provided the dependencies are fulfilled.
Keep to the following syntax rules when creating makefiles:
To demonstrate make in a practical situation, let's look at a makefile that helps users create books with LaTeX. The book is stored in multiple documents; in other words, there is a Tex file for each chapter. LaTeX will compile these components to create a file called book.tex.
First create the DVI file. We want make to call the latex command whenever the source files change after this.
book.dvi: chap01.tex chap02.tex chap03.tex \
chap04.tex chap05.tex chap06.tex \
chap07.tex book.tex
latex book
We will be using the Dvips program with a variety of parameters to automatically create a Postscript file. The tool has nothing to do, unless the DVI file for the first target has changed:
book.ps: book.dvi
dvips -q -o book.ps book
If you like, you can add another target to create a PDF document from the Postscript file:
book.pdf: book.ps
ps2pdf book.ps book.pdf
A good backup is definitely worthwhile after all that work. It makes sense to bundle the Tex files, the Postscript file, and PDF into a compressed Bzip2 tar archive, and then run SCP to copy it to a remote machine - better be to safe than sorry:
backup: chap01.tex chap02.tex chap03.tex \
chap04.tex chap05.tex chap06.tex \
chap07.tex book.tex buch.ps \
book.pdf
tar cvfj backup.tar.bz2 *.tex book.ps book.pdf
scp backup.tar.bz2 huhn@asteroid.huhnix.org:
There are various options for using makefiles like this. If you run make without passing in any other parameters, make will simply process the first target, that is, a DVI file if you have modified one or more Tex files.
As an alternative, you can pass a different target in to make when you call the tool, for example make backup, to create a safe copy, or make buch.pdf to create the PDF document.
Just as a reminder: make creates the PDF from the Postscript file by calling the ps2pdf command; the Postscript file is created from the DVI file, which is the makefile's first target. If anything has changed on the way to the Postscript file, make will process all the targets from the top down (Figure 1). If there is nothing to do, make will let you know:
make: `buch.pdf' is up to date.
Make has a number of other command line parameters. If the control file uses a name that make does not associate with a makefile, you need to pass in the filename, along with instructions for processing it, by setting the -f flag:
make -f controlfile
It is also possible to specifically name the working directory. If you are currently at a different location on the filesystem, you can use the -C parameter to tell make where to go to work:
$ make -C ~/book make: Entering directory `/home/huhn/book' latex book ... make: Leaving directory `/home/huhn/book'
If the source files haven't changed, you can "force" a build with the -B option:
$ make -B book.pdf latex book ... Transcript written on book.log. dvips -q -o book.ps book ps2pdf book.ps book.pdf
And if you are interested in finding out what is going on under the hood, you can set the -d (for debug) option for verbose output (Figure 2). To prevent the output from scrolling off the screen, you might like to pipe it to a pager such as less or more:
make -d | less
The LaTeX example uses a couple of Tex files, which keeps the makefile fairly readable. When the number of source files starts to grow, it is easy to lose track. To prevent this, make gives you the option of defining variables.
To assign a variable called TEXFILES to the LaTeX files, you define the variable at the start of the Makefile:
TEXFILES = chap01.tex chap02.tex chap03.tex \
chap04.tex chap05.tex chap06.tex \
chap07.tex book.tex
Then reference the variable in the makefile, as $(VARIABLENAME), for example:
book.dvi: $(TEXFILES)
latex book
Make also has some standard variables. For example, $@ refers to the current target, and $? refers to modified dependencies, that is, to the files that follow the colon.