This is part of the tutorial of UNIX Commands.

Walking around in a UNIX file system

In this part of the tutorial, I'll give an introduction of the basic commands to look around and move around in the filesystem.

Know where you are

A first thing we'd like to discover is where we are in our filesystem. For this purpose, you can issue a pwd command and it'll give you the current directory where you are. As an example, I can issue the pwd command from the point where I start, e.g.

[johndoe@computer johndoe]$ pwd
/home/johndoe

The compute tells me I'm in the directory johndoe which is part of the directory home. Usually, all users' data is stored in the home directory, under the directory with their login name (/home/johndoe is called the home directory of user johndoe). There is one higher level, the / directory, which is also called the root directory. There is no higher level than this root directory.

There are some small differences with the Windows operating system:

List the files in the current directory

Basic file lists

In order to list the files in your current directory, you can issue the ls command, e.g.

[johndoe@computer johndoe]$ ls
dir1   file1  file2  file3

Note that there are 3 files in my directory, namely file1, file2 and file3, and 1 directory which I named dir1. Most UNIX distributions use a color scheme so you'll be able to distinguish directories from files. In my setup (which is pretty common), directories are colored in blue, while other files are normally colored. Some other files (such as images or archived files) may even be colored differently.

More information

We can get more information of our files by adding the -l parameter to our ls command, which will print out our directory contents as a list (that's where the -l comes from, e.g.

[johndoe@computer johndoe]$ ls -l

total 4 drwxrwxr-x 2 johndoe johndoe 4096 Sep 27 19:21 dir1 -rw-rw-r-- 1 johndoe johndoe 0 Sep 27 19:18 file1 -rw-rw-r-- 1 johndoe johndoe 0 Sep 27 19:18 file2

-rw-rw-r-- 1 johndoe johndoe 0 Sep 27 19:18 file3

This list gives more stats about the files in my home directory than the simple ls command. The characters in the beginning show me the access modi of the files (I'll try to get into that in a later part). The d character in the beginning of the line for dir1 tells me it is a directory. The johndoe strings tell me that johndoe is the owner of the files. Next are the sizes of the files (by default, a directory takes up 4 kilobytes). You can clearly see all of the files are empty, as their sizes are 0. The date and time denote when the last changes to the files were made.

Hidden files

Upon the creation of your home directory, some extra hidden files were created that are placed in your home driectory. A hidden file in UNIX is simply a file whose name starts with a "." character. You can show these files by adding the -a (for "all") parameter, e.g.

[johndoe@anthony-laptop johndoe]$ ls -a

. .bash_history .bash_profile dir1 file1 file3 .kde

.. .bash_logout .bashrc .emacs file2 .gtkrc .xauthGrxNix

Most of these files (and directories) contain default settings for various standard programs. There are two special directories, too. The . directory points to the current directory, and the .. directory points to the directory which is one step closers to the root directory.

You can combine the -a and -l parameters in one parameter -al (or -la), e.g.

[johndoe@computer johndoe]$ ls -al

total 44 drwx------ 4 johndoe johndoe 4096 Sep 27 19:21 . drwxr-xr-x 5 root root 4096 Sep 27 01:54 .. -rw------- 1 johndoe johndoe 63 Sep 27 16:18 .bash_history -rw-r--r-- 1 johndoe johndoe 24 Sep 27 01:54 .bash_logout -rw-r--r-- 1 johndoe johndoe 191 Sep 27 01:54 .bash_profile -rw-r--r-- 1 johndoe johndoe 124 Sep 27 01:54 .bashrc drwxrwxr-x 2 johndoe johndoe 4096 Sep 27 19:21 dir1 -rw-r--r-- 1 johndoe johndoe 854 Sep 27 01:54 .emacs -rw-rw-r-- 1 johndoe johndoe 0 Sep 27 19:18 file1 -rw-rw-r-- 1 johndoe johndoe 0 Sep 27 19:18 file2 -rw-rw-r-- 1 johndoe johndoe 0 Sep 27 19:18 file3 -rw-r--r-- 1 johndoe johndoe 120 Sep 27 01:54 .gtkrc drwxr-xr-x 3 johndoe johndoe 4096 Sep 27 01:54 .kde

-rw------- 1 johndoe johndoe 59 Sep 27 19:04 .xauthGrxNix

Note that the upper level directory .. is owned by the root, the administrator or "superuser" of a UNIX system. This directory is restricted, and you thus cannot do anything in that directory, unless you are the root user.

Creating new files

In order to create a new (empty) file, you can issue the touch command, where the parameter is the name of the file, e.g.

[johndoe@computer johndoe]$ touch newfile

[johndoe@computer johndoe]$ ls

dir1 file1 file2 file3 newfile

The file named newfile has been created, as can be seen in the file list I issued after "touching" the file. The touch command was originally built for bringing a file up-to-date, i.e. changing its date and time of last changes to the current date and time. But if the file you want to touch does not exist, it creates a new empty file for you.


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