The Command Line (continued)

What you interact with in a Linux terminal window is called a shell -- a piece of software that provides access to the operating system's kernel. All you really need to know about it is that all Linuxes (and Mac OS X for that matter) use a shell called Bash -- short for the Bourne-again Shell, a development of one of the original Unix shells called, not surprisingly, the Bourne Shell.

Below is a collection of tips and tricks you might find useful for finding your way around Bash.

Detailed information
You can always find detailed information about a shell command by prefixing it with man (short for "manual"). So man ls for example will tell you all you need to know about the ls command.


Navigate through man with the <Page Up>, <Page Down> and arrow keys. Press Q to quit.


Directory and file stuff
As you'll see above, the ls command lists a directory's contents. At its most basic it does so on a single line:



but adding an optional argument -- this case ls -l -- provides more detailed output:



Any file prefixed with  a dot (.) in Linux is considered "hidden". That doesn't mean they're super-secret or anything like that. It's simply an indication that they're system files not usually of interest to the average user.

You can see all hidden files by adding the -a parameter:



Parameters can be combined. For example ls -la yields (in part):



Linux defaults to displaying file sizes in blocks, so one very useful parameter that works on many file-related commands is -h. It converts blocks in human-readable format -- eg. 1K, 234M, 5G, etc.

Try comparing the output of df ("show disk usage") and df -h and you'll see the difference:





Whoa, hold on a sec. Did you just get a concise display of the size, use and free space available on all the disks available to your machine -- including those on the network -- from a simple two-letter command? Yep. That's the power of the Linux command line!

Here are a few more commands to try:

cat	Concatenate and display the contents of file(s).
cd	Change directory. (cd on its own will always take you back to your /home directory.)
cp	Copy one of more files.
du	Show disk usage.
file	Determine a file's type.
grep	Search file(s) for lines containing a match to a given pattern.
head	Display the first part of a file.
history	Show command history
ifconfig	Display (and optionally configure) network interfaces.
locate	Find files.
lsof	List all output files.
lsusb	List all USB devices.
mkdir	Make a directory.
more	Display output one screen at time.
ps	Show process status. (Eg: ps -e)
pwd	Print working (current) directory.
rename	Rename file(s).
rm	Remove file(s).
rmdir	Remove directory.
tail	Output the last part of a file.
top	List all processes running on the system. (Press Q to quit.)
whomai	You mean you really don't know? ;-)

You'll find a much more comprehensive list here.


Quick links to previous parts:
Part I, Part II, Part III, Part IV, Part V