How do I read the source code of shell commands?

Question

I would like to read the actual source code which the linux commands are written with. I've gained some experience using them and now I think it's time to interact with my machine at a deeper level.

I've found some commands here http://directory.fsf.org/wiki/GNU. Unfortunately I wasn't able to find basic commands such as 'ls' which seems to me easy enough to begin.

How exactly do I read the source code of the simple shell commands like 'ls'? I'm running on Ubuntu 12.04

Answer 1

All these basic commands are part of the coreutils package.

You can find all information you need here:

http://www.gnu.org/software/coreutils/

If you want to download the latest source, you should use git:

git clone git://git.sv.gnu.org/coreutils

To install git on your Ubuntu machine, you should use apt-get (git is not included in the standard Ubuntu installation):

sudo apt-get install git

Truth to be told, here you can find specific source for the ls command:

http://git.savannah.gnu.org/cgit/coreutils.git/tree/src/ls.c

Only 4984 code lines for a command 'easy enough' as ls... are you still interested in reading it?? Good luck! :D

Answer 2

Direct links to source for some popular programs in coreutils:

• cat (767 lines)
• chmod (570 lines)
• cp (2912 lines)
• cut (831 lines)
• date (570 lines)
• df (1718 lines)
• du (1112 lines)
• echo (272 lines)
• head (1070 lines)
• hostname (116 lines)
• kill (312 lines)
• ln (651 lines)
• ls (4954 lines)
• md5sum (878 lines)
• mkdir (306 lines)
• mv (512 lines)
• nice (220 lines)
• pwd (394 lines)
• rm (356 lines)
• rmdir (252 lines)
• shred (1325 lines)
• tail (2301 lines)
• tee (220 lines)
• touch (437 lines)
• wc (801 lines)
• whoami (91 lines)

Full list here.

Answer 3

ls is part of coreutils. You can get it with git :

git clone git://git.sv.gnu.org/coreutils

You'll find coreutils listed with other packages (scroll to bottom) on this page.

Answer 4

Actually more sane sources are provided by http://suckless.org look at their sbase repository:

git clone git://git.suckless.org/sbase

They are clearer, smarter, simpler and suckless, eg ls.c has just 369 LOC

After that it will be easier to understand more complicated GNU code.

Answer 5

CoreUtils referred to in other posts does NOT show the real implementation of most of the functionality which I think you seek. In most cases it provides front-ends for the actual functions that retrieve the data, which can be found here:

It is build upon Gnulib with the actual source code in the lib-subdirectory

Answer 6

You can have it on github using the command

git clone https://github.com/coreutils/coreutils.git

You can find all the source codes in the src folder.

You need to have git installed.

Things have changed since 2012, ls source code has now 5309 lines

Answer 7

BSD distributions are actually a nice way of reading the source code, by using their repositories, since it is all packed into one place, and you can view how historically the source code has evolved, or changed. So why not use BSD repos , such as NetBSD or OpenBSD for this task.

Answer 8

    cd ~ && apt-get source coreutils && ls -d coreutils*     

You should be able to use a command like this on ubuntu to gather the source for a package, you can omit sudo assuming your downloading to a location you own.