Before you get started, type
pwd
and make sure that the output ends with tfcb_2021/lectures/lecture03.
If not, go back to the tutorial instructions.
Don’t hesitate to ask questions if you get stuck!
To get started, simply type
ls
and hit return.
This shows the collection of files that are in your current directory (a.k.a. folder).
The name ls is an abbreviation for “list”.
This is the simplest type of shell command invocation.
Next just mash the keyboard making a random command, like this:
asdfasfkjaeasdkjaadsfkljaeflkwae
What happens?
More generally, shell commands look like
command flags arguments
where flags and arguments are optional.
We separate these components with spaces (extra spaces are fine).
Try this command with an argument:
ls /
Here we are passing / to the ls command as an argument to tell it which directory should be listed.
Specifically, we are telling it to list the very “bottom” directory of the file system, which in unix is named /.
We will discuss directory structure later.
Now try
ls asdfasdf
which should give an error unless you happen to have a file named asdfasdf in your current directory.
Errors are OK.
They don’t cause any harm, and are a natural part of working in the shell.
Try this command with a flag:
ls -1 /
Here -1 is a flag which specifies that the listing should happen in a single column.
Flags generally go before the arguments, but some commands will allow them in any order.
Does ls allow flags after arguments?
Try it out!
Flags modify some form of the command behavior, and can range from simple to rather complex.
Flags can have arguments, like
ls -w 50 /
in which we give the -w flag the value of 50.
The -w flag tells ls that the user wants to wrap output to some number of letters wide and no wider, in this case 50 letters wide.
Try varying the argument to -w from very small to very large.
Are negative numbers allowed?
All flags start with a dash , like -1 and -w did.
They can be longer than one letter, such as -name.
Some flags start with two dashes, like --verbose.
Generally two-dash flags are for long names and single-dash flags are for short names, but this convention isn’t always consistently applied.
For example, try using --width in place of -w in the command above.
Does -width work?
Try ls / with and without using the -a flag.
Then try the -a and -1 flags together as ls -a -1.
Try
cat vader.txt
This is a handy way to look at small files. Now try
cat sequence.gb
This is not a very convenient way to view a long file, because it spits out the whole file and you will no longer be able to see the top.
A better way is to use less.
Before we try that, note:
you can navigate in less using the arrow keys, and exit using the letter q.
Try
less sequence.gb
and have a look around this file.
Exit that less session using q.
Many commands have built-in help using -h or --help.
Try
less --help
to find the commands that allow you to move forward and backward by page, and use them to view sequence.gb.
man: the built-in manualFor more in depth help see the command man, which is short for “manual.”
The argument to man is the command you want to see documentation for.
Try
man man
to learn about the command man.
Look at the overall structure of the document. What does the top describe? What about the rest?
Use any method you like to find documentation about the wc command, then use it to count the number of lines in sequence.gb.
Similarly, look at the documentation for the ls command to learn about the -a flag.
Congratulations! You now know how to navigate around the file system.
For the next step, look at the README file in the 02-directories directory to work through the next part of the adventure.