I am trying to read some linux source code, not about the kernel, just some utilities such as ls, grep, wget,etc. But after I download the source code, I found there are so much things, I do not know where to start. There are makefile, m4, configure.ac files. Where could I start? Need I to learn some other things, such as linux auto tools? Thanks in advance.

If you don;t know what a makefile is, start by learning the C language and gcc.

I can program using makefile. But I don't know much about the auto tools in linux. I think the source code's makefile is created by auto tools, not by hand. So reading the makefile is very difficult.

Start reading!

For instance, start here: info automake

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Now, let me please set the stage for you. Let's start here: http://en.wikipedia.org/wiki/Automake (Do not keep reading until after you have actually read that page!! I mean it! Scout's Honor!)

The magickal folks who wrote all those tools intended for them to "just work" on ... an IBM mainframe, an AS/400, your Kindle Fire, your Windows PC, your Macintosh, your portable phone (or any and every flavor), or any of the several-dozen(!) hardware platforms supported by Unix/Linux.

And ... they do!

Thought Question: How?

The answer ... is Automake.

When you install a new package from source-code, the first command that you execute is: ./Configure. And this executes a whole slew of "discovery" steps that determine exactly what your hardware and software environment is. Based on this, Automake constructs an appropriate Makefile, and everything else that is needed, so that "everything 'Just Works'" on your environment.

If what I just said sounds like "effin' brilliant Voodoo ..." ... trust me: it is. There be Gods in these woods. Infinitely More than Wyzards. These be not Mortal folk.

This help me a lot, thank you very much!