Files and Directories
In Unix, all data are stored in repositories called files.
For example, the RESOLVE/C++ programs that you write in this course will
be stored as Unix files. You could also use files to store any reports
that you write or to save the e-mail that you receive.
Like in the "real" world, it is not a good idea to have lots of files
"lying around" in a disorganized manner. Unix allows you to organize your
files into directories. A "directory"
is a location where files are kept in a list. For instance, you could create
a directory to store all your files for the first lab and call it Lab1.
You could create another directory called
Lab2 to store your files
for the second lab. If you are already familiar with either Apple Macintosh
computers or Windows File Manager, just think of Unix directories as being
the same as folders.
When you login to a Unix system, the system puts you in your home
directory. Your home directory is the directory that is assigned
to you to store all your files. Unix has commands that you can use to create
and delete files and directories within your home directory. Unix also
gives you commands to change from your home directory to other directories.
The directory that you're in at any given point of time is called your
current
working directory.
The ls command
The Unix command ls, lists the contents of the current working directory.
The contents of a directory are the files and sub-directories inside that
directory.
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In the xterm, enter the command: ls
Since your working directory at this point is your home directory,
the output of the ls command tells you the contents of your home
directory.
In the xterm, enter the command: Ls
You'll get an error message of the form:
Ls: Command not found.
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Important Note: Unix is case-sensitive. That means it treats
ls
and Ls as two distinct commands. In fact, there is no command Ls
in Unix. Similarly, if you have a file named foo, you cannot access
it using the name FOO.
The mkdir command
You can use the mkdir command to create new directories. In the
home directory, let us create a directory called Testdir1.
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Enter the command: mkdir Testdir1
If you repeat the ls command, you'll see that Testdir1
appears among the contents listed. Let us use the cd command to
change our working directory to Testdir1.
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The cd command
You can move around from one directory to another with the cd command.
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Enter the command: cd Testdir1
At this point, you're not in your home directory anymore but in
the sub-directory Testdir1. What command do you think you should
choose if you wanted to create a sub-directory Testdir2 within this
directory?
Go ahead and enter the command to create a new sub-directory Testdir2
in your xterm. Use the ls command to verify that the directory was
created.
Now Testdir2 is a sub-directory of Testdir1, which
is a sub-directory of your home directory.
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Naming the current and parent directories
To review, we have seen how we can change to a particular directory by
using the cd command followed by the name of the directory. Unix
uses the special name .. (pronounced "dot dot") to refer to the
parent directory of a particular directory. Note that each directory can
have only one parent directory. The special name . ("dot") is used
to refer to the current working directory. You can use these special names
with the Unix commands that work with directories.
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Enter the command: cd ..
This puts you in the parent directory of the current working directory.
Now you should be back in your home directory.
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Naming other directories
Earlier we used the ls command to list the contents of the current
working directory. You can use ls to look at the contents of a directory
other than the one you're currently in, by specifying the directory. Let
us list the contents of the sub-directory Testdir1.
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Enter the command: ls Testdir1
Actually, you could use ls to list the contents of the directory
Testdir2
(in the sub-directory Testdir1), while you're still in your home
directory. At this point, Testdir2 should be empty.
Enter the command: ls Testdir1/Testdir2
In this case, you have specified the directory to be listed using
what is called a relative pathname.
A relative pathname specifies a route to get to the desired file or directory
starting from the current working directory. In other words, a relative
pathname also contains the name of each intermediate directory that you
need to pass through to get to the desired destination. The names are separated
by the "/" character. All components of a relative pathname except the
last, must be directory names. The last component can be either a file
name or a directory name.
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Last modified: Tue Jan 6 20:27:59 EST 1998
