[WIP]Unix / Linux for Beginners

創建: 2022/12/9

 https://www.tutorialspoint.com/unix/index.htm

Get Started

 Kernel

The kernel is the heart of the operating system. It interacts with the hardware and most of the tasks like memory management, task scheduling and file management.

 Shell

The shell is the utility that processes your requests. When you type in a command at your terminal, the shell interprets the command and calls the program that you want. The shell uses standard syntax for all commands. C Shell, Bourne Shell and Korn Shell are the most famous shells which are available with most of the Unix variants.

 Commands and Utilities

There are various commands and utilities which you can make use of in your day to day activities. cp, mv, cat and grep, etc. are few examples of commands and utilities. There are over 250 standard commands plus numerous others provided through 3rd party software. All the commands come along with various options. 

 Files and Directories

All the data of Unix is organized into files. All files are then organized into directories. These directories are further organized into a tree-like structure called the filesystem. 

 Examples

•  login
• passwd
• cal
• ls
• whoami
• users, who, w
• logout
• halt, init 0, init 6, poweroff, reboot, shutdown

File Management

 Files' Type

 

Ordinary Files	An ordinary file is a file on the system that contains data, text, or program instructions.
Directories	Directories store both special and ordinary files. For users familiar with Windows or Mac OS, Unix directories are equivalent to folders.
Special Files	Some special files provide access to hardware such as hard drives, CD-ROM drives, modems, and Ethernet adapters. Other special files are similar to aliases or shortcuts and enable you to access a single file using different names.

Listing Files

 

ls

 

 

ls

ls -l

 

$ls -l
total 1962188

drwxrwxr-x  2 amrood amrood      4096 Dec 25 09:59 uml
-rw-rw-r--  1 amrood amrood      5341 Dec 25 08:38 uml.jpg
drwxr-xr-x  2 amrood amrood      4096 Feb 15  2006 univ
drwxr-xr-x  2 root   root        4096 Dec  9  2007 urlspedia
-rw-r--r--  1 root   root      276480 Dec  9  2007 urlspedia.tar
drwxr-xr-x  8 root   root        4096 Nov 25  2007 usr
drwxr-xr-x  2    200    300      4096 Nov 25  2007 webthumb-1.01
-rwxr-xr-x  1 root   root        3192 Nov 25  2007 webthumb.php
-rw-rw-r--  1 amrood amrood     20480 Nov 25  2007 webthumb.tar
-rw-rw-r--  1 amrood amrood      5654 Aug  9  2007 yourfile.mid
-rw-rw-r--  1 amrood amrood    166255 Aug  9  2007 yourfile.swf
drwxr-xr-x 11 amrood amrood      4096 May 29  2007 zlib-1.2.3
$

 

First Column

Represents the file type and the permission given on the file. Below is the description of all type of files.

-	Regular file, such as an ASCII text file, binary executable, or hard link.
b	Block special file. Block input/output device file such as a physical hard drive.
c	Character special file. Raw input/output device file such as a physical hard drive.
d	Directory file that contains a listing of other files and directories.
l	Symbolic link file. Links on any regular file.
p	Named pipe. A mechanism for interprocess communications.
s	Socket used for interprocess communication.

 

Second Column

Represents the number of memory blocks taken by the file or directory.

Third Column

Represents the owner of the file. This is the Unix user who created this file.

Fourth Column

Represents the group of the owner. Every Unix user will have an associated group.

Fifth Column

Represents the file size in bytes.

Sixth Column

Represents the date and the time when this file was created or modified for the last time.

Seventh Column

Represents the file or the directory name.

 

ls -a

Metacharacters

 

*	to match 0 or more characters
?	to match with a single character

Hidden Files

An invisible file is one, the first character of which is the dot or the period character (.). Unix programs (including the shell) use most of these files to store configuration information.

Creating Files

 

vi filename

 

Editing Files

Display Content of a File

 

cat filename

 

• -b with line number

Counting Words in a File

 

wc filename1( filename2 ...)

 

 

$ wc filename
2  19 103 filename
$

 

First Column	Represents the total number of lines in the file.
Second Column	Represents the total number of words in the file.
Third Column	Represents the total number of bytes in the file. This is the actual size of the file.
Fourth Column	Represents the file name.

 

Copying Files

 

cp source_file destination_file

 

Renaming Files

 

mv old_file new_file

 

Deleting Files

 

rm filename

 

rm filename1 filename2 filename3

 

 

Standard Unix Streams

 

stdin	This is referred to as the standard input and the associated file descriptor is 0. This is also represented as STDIN. The Unix program will read the default input from STDIN
stdout	This is referred to as the standard output and the associated file descriptor is 1. This is also represented as STDOUT. The Unix program will write the default output at STDOUT
stderr	This is referred to as the standard error and the associated file descriptor is 2. This is also represented as STDERR. The Unix program will write all the error messages at STDERR.

Directories

File Permission

Environment

Basic Utilities

Pipes & Filters

Processes

Communications

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