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= Linux File System =
<source lang="bash"># display files and directories below root (/) with the tree command
$ tree /
/
|-home| |-lesuser1| |-markuser2| |-uli101user3| ...
|
|-binpublic| |- ipc144| |-nled
|
....
This course will teach you the skills you require to navigate the directory tree in a Linux file system because learning command-line navigation of the file system is essential for efficient system usage and administration.
= Some = Typical Unix/Linux directories directly below root Directories ==
A sample of some of the commonly found subdirectories that lie below the root directory (<code>/</code>) is shown in the table below. The table includes a brief description of the purpose of that subdirectory.
{|
| <code>/</code>
| Root directory (ancestor to all directories).
|-
| <code>/home</code>
| Used to store usersf home directories.
|-
| <code>/bin</code>
| Common system binaries (commands).|-| <code>/usr/bin</code>| Common utilities (commands) for users.
|-
| <code>/devusr/sbin</code>| Device files (terminals, printers, etcCommon utilities for user administration.)
|-
| <code>/etc</code>
| General System Admin. Files (eg passwd).
|-
| <code>/usr/binvar</code>| Common utilities Dynamic files (commandslog files) for users|-| <code>/usr/sbin</code>| Common utilities for user administration.
|-
| <code>/tmp</code>, <code>/var/tmp</code>
| Temporary files for programs.
|-
| <code>/vardev</code>| Dynamic Device files (log filesterminals, printers, etc.).
|}
== Home directory ==
* Almost every Every user in a Linux file system gets when receiving an account has a ''home'' directory when their account was created.* This is where the users you keep their your personal files* The <code>~</code> symbol represents the your home directory of the logged in user.* The * You can use the <code>~</code> symbol may be used in file pathnames. More about file pathnames later.* The A <code>cd</code> command when used without any other parameters gets argument will get you into directly to your home directory no matter where you previously were in the Linux file system.* As Linux is a multi-user filesystem, remember Remember to keep your files private. You shall learn how to do this in a later class.
== Types of Files ==
On a Unix/Linux file system a ''file'' can be anything. To an average computer user a file is a container for: a text document, video, music, photo and so onetc.
A directory is a special type of file (index file) containing references to other file locations on the physical disc or to other file related information. Even devices Devices like a terminal, a scanner, or a printer are also files. You will learn more details about these types of files later in this course. Any file (or directory) name starting with a period (such as <code>.</code> or <code>..</code>) is considered a hidden file (or directory). You can use the <code>ls -l</code> command to determine the type of file.
For Example:
* Use the <code>-l</code> option of the <code>ls</code> command to get detailed information about a file.
* Use the <code>-ld</code> option of the <code>ls</code> command to get detailed information for just the directory.itself, not the filenames within it
* The first character in detailed listing determines the file type, so:
** <code>-</code> indicates a regular file
** b or c indicates a device file
** d indicates a directory file
</blockquote>
== Hidden Files = === What are hidden files? ===
A filename that begins with a '<code>.</code>' is a hidden file. So, if a filename name starts with a '<code>.</code>' as its first character, like <code>.profile</code> for example, it is a considered to be a hidden file by Linux commands and is suppressed from the normal listing of files. See the examples shown below:
* <code>pwd</code> displays the present working directory. This command is used to display where on in the Linux file system the logged in user is presently working in. In the example shown above, that location is <code>/home/murray</code>
* <code>ls</code> displays the normal listing of file, i.e. all non-hidden files in the present working directory (this is usually abbreviated to pwd in these notes).
* <code>ls -a</code> displays all files, i.e. including hidden and non-hidden files, in the present working directory. In the listing of <code>ls -a</code> the first two items (i.e. * '<code>.</code>' and '<code>..</code>') directories are hidden directories to indicate the present working directory (the item: '<code>.</code>') and the item '<code>..</code>' indicates the parent directory of the present working directory. Both (<code>.</code> and <code>..</code>) are found in every directory in the Linux file system. They cannot be removed, by any user, because both these directories are required for the internal working of the Linux file system.* <code>ls -A</code> displays 'almostAlmost' all files, that is all hidden files like <code>.profile</code> except the first two items <code>.</code> and <code>..</code>. This means not including <code>.</code> and <code>..</code> are never shown within the <code>ls -A</code> output listing.
</blockquote>
== Working With The File System ==
* Be very careful when working with files on the command line, as there is no undo command or a Trash/Recycling Bin
* You will learn later additional ways to control file access through file permissions which will help you prevent accidental file damage or deletion
== Basic Commands == ; <code>pwd</code>: Used to display the user’s present working directory. A user may need to know where they are located on the computer system in order to build directories, copy files, etc.; <code>cd</code> ''directorypath'': Used to change to a directory. Entering the cd command without a directory name will change to the user’s home directory.; <code>ls</code>: Used to display the contents of a directory (eg. regular files or sub-directories). By default, the ls command displays non-hidden filenames only.;* The following are common options available with the <code>ls</code> command:;* <code>-a</code> short display of hidden & non-hidden files;* <code>-l</code> detailed display of files (excl. hidden files);* <code>-d</code> combined with <code>-l</code> option, displays info about the directory itself instead of the files within it;* Options can be combined, for example: <code>ls -la</code> (or <code>ls -l -a</code>)
{|
| spacebar<SPACEBAR>
| Move to next screen
|-
| Move to previous screen
|-
| enter<ENTER>
| Move to next line
|-
| /car<ENTER>
| Search for pattern "car"
|-
| Exit to shell
|}
</ddblockquote><dt>; <code>less path/to/file</code></dt>''filepath''<dd><p>: Works like more command, but contains more navigation features.</p></dd><dt>; <code>touch path/to/file</code></dt>''path''<dd><p>Updates : Used to update the date and time of existing files. The <code>touch </code> command is also used to create empty files. You will be using the touch command to create empty files when you practice the file management on-line tutorial</p></dd><dt>; <code>file path/to/file</code></dt>''path''<dd><p>: Determines a file type . Useful when a particular file has no file extension or the extension is unknown/or incorrect</p></dd></dl>.
== The find Command ==
The <code>find </code> command allows searching for files by file name, size as well as , and file attributes recursively throughout the file system. An optional action can be performed on matches
<source lang="bash">#Search for a file named bob:
find . -size +100M
</source>
== File Naming ==
* Unix/Linux is case sensitive!
* Adopt a consistent file naming scheme . this will help you find your files later
* Make your file and directory names meaningful
* Avoid non alphanumeric characters, as they have a special meaning to the system and will make your work more difficult
* Avoid using spaces in file names . - consider periods, hyphens and underscores instead
* Feel free to use file name extensions to describe the file purpose
== Getting Help with Commands ==
* A comprehensive online manual for common UNIX/Linux commands exists on your server
-k provides short (one-line) explanation relating to the commands matching the character string.
</pre>
== Text Editing ==
Editing text files is an everyday activity for both users as well as administrators on a Unix and Linux system
As the GUI may not always be available, knowing command-line text editors is a very valuable skill.
* If needed, use the <code>unix2dos </code> and <code>dos2unix </code> utilities to convert between the two systems
* A specific system may have many editors available and as you work with one for a while you will probably pick a favourite one
* A traditional fall-back is the <code>vi </code> editor, as it is most likely to be present on all Unix-like systems, especially when installed with a minimum software complement
Consider knowing <code>vi </code> as one of many badges of a competent Unix/Linux user
* <ulcode>vi<li/code><p>Vi has a relatively steep learning curve and is not user friendly, but it offers nice advanced features which will be introduced later in the course</p><p>(Visual) Editor</p></li></ul>
<code>vi </code> is a powerful, interactive, visually-oriented text editor with these features:
* Efficient editing by using keystrokes instead of mouse.
* Possibility to recover files after accidental loss of connection
* Features for programmers (eg. line numbering, auto-indent, etc)
* Although you may prefer to use other editors (such as <code>nano </code> or <code>nled</code>), knowing <code>vi </code> is very useful, as this is one editor that is present on all Unix-like systems
There are two ways to start an editing session with <code>vi</code>:
There are three operational modes while using the vi editor:
You can move around to text in the screen by using the following keys:
| $
| end of line
|-
| G
| go to last line in file
|-
| 237G
| go to line 237 in file
|}
* You may be able to move around by using the arrow keys (depends on version of vi).
While in command mode, you can issue the following commands to input text:
| insert line below current line
|-
| 0O
| insert line above current line
|-
|-
| r
| replace characterunder cursor
|-
| R
| overwrite textcharacter-by-character
|}
{|
| x
| Delete single characterunder the cursor
|-
| d
| Delete
|-
|
| eg. dw - delete from the current position to the next word or special character
|-
|
| eg. d$ - delete from the current position to the end of the line
|-
|
| eg. dd - delete the entire current line
|-
| c
| Change
|-
|
| eg. cw - change from the current position to the next word or special character
|-
|
| eg. c$ - change from the current position to the end of the line
|-
|
| eg. cc - change the entire current line
|-
| y
| Yank (copy)
|-
|
| eg. yw - copy from the current position to the next word or special character
|-
|
| eg. y$ - copy from the current position to the end of the line
|-
|
| eg. yy - copy the entire current line
|-
| p
| paste deleted or copied text after or below cursor
|-
| P
| paste deleted or copied text before or above cursor
|-
| u
<blockquote>Editing commands can be preceded with a number, for example: 3x = delete the next three characters 2u = undo the last two edits 12dd = delete 12 lines
</blockquote>
Search for text (in command mode)
| n
| Display next match
|}
* Work performed during vi session is stored in a Work Buffer (temporary storage) until the user saves their work.