Linux: Basic Command Introduction

裘子惠

　　1. File Name convention:
　　1) All characters except '/' are regarded as legal as '/' is used for file path delimeter.
　　2) Space, Tab, Backspace, @, #, $, &, (, ) and - are not recommanded to be used as file name.
　　3) Do not use '.' as the first character of file name. Because file name starts with '.' is regarded as hidden file.
　　4) File name is case sensitive. Linux is case sensitive.
　　
　　2. Basic comman format:
　　1) Command -Options Params
　　Eg: ls -al /etc
　　1) When we have multiple options, we can put them together.
　　2) . represents current folder and .. represents parent folder.
　　2) Command can be categorized into two kinds:
　　1) root command
　　usually stored in /sbin or /usr/sbin folder with the format of binary file.
　　2) user command
　　usually stored in /bin or /usr/bin folder with the format of binary file.
　　
　　3. Command Intro:
　　1) Command Name: ls
　　Command Derived From: list
　　Command Path: /bin/ls
　　Command Permission: all users
　　Command Description: show all the dirs and files in current path
　　Command Syntax: ls [-ald] [file or dir]
　　a: Show all files including hidden files.
　　l: Show detail information
　　d: Show current folder properties
　　Result Sample:
　　drwxrwxr-x  6 administrator administrator      4096 Aug 17 23:25 apache-maven-3.1.0
　　-rw-rw-r--  1 administrator administrator   5439122 Aug 17 23:24 apache-maven-3.1.0-bin.tar.gz
　　Explaination:
　　1) The first letter: Means the file format.
　　'd' means Directory.
　　'-' means Binary file.
　　'l' means soft link file.
　　2) The following 9 letters: Means the authority of three kind of user.
　　File owner(u) -> The user that created the file/folder. And it can also be transfered to another person.
　　User group(g) -> The user group that has the right of controlling this file.
　　Others(o) -> ...
　　3) The digit 6 or 1 means the hard link count. Will explain later.
　　4) The following 'administrator' means the owner of this file.
　　5) The following 'administrator' means the belonged group of this file.
　　6) The following '4096' and '5439122' means the size of this file/folder. But this is not accurate when applied with folder size.
　　7) The timestamp means the file creation date or last modified date.
　　
　　2) Command Name: cd
　　Command Derived From: change directory
　　Command Path: shell imbeded command
　　Command Permission: all users
　　Command Description: change current directory
　　Command Syntax: cd [path]
　　Example:
　　cd /      change to root folder
　　cd ..     change to parent folder
　　
　　3) Command Name: pwd
　　Command Derived From: print working directory
　　Command Path: /bin/pwd
　　Command Permission: all users
　　Command Description: show current direcory
　　Command Syntax: pwd
　　
　　4) Command Name: mkdir
　　Command Derived From: make directories
　　Command Path: /bin/mkdir
　　Command Permission: all users
　　Command Description: create new directory/folder
　　Command Syntax: mkdir [dir name]
　　Example:
　　mkdir /test -> Make directory under the context of root folder.
　　mkdir test -> Make directory under the context of current working directory.
　　
　　5) Command Name: touch
　　Command Path: /bin/touch
　　Command Permission: all users
　　Command Description: create a new blank file
　　Command Syntax: touch [file name]
　　Example:
　　touch newfile
　　
　　6) Command Name: cp
　　Command Derived From: copy
　　Command Path: /bin/cp
　　Command Permission: all users
　　Command Description: copy file or folder
　　Command Syntax: cp  -R [source folder name] [dest folder name]
　　[source file name] [source file name] ... [dest folder name] [dest folder name] ...
　　Example:
　　cp Test.java ..
　　cp Test1.java Test2.java Test3.java ..

    7) Command Name: mv　　Command Derived From: move
　　Command Path: /bin/mv
　　Command Permission: all users
　　Command Description: move file/folder location; rename file/folder
　　Command Syntax: mv [source folder name] [dest folder name]
　　[source file name] [source file name] ... [dest folder name] [dest folder name] ...
　　Example:
　　mv Test.java Test1.java --> Rename
　　mv /home/administrator/Test/Test1.java  /home/administrator/Test2.java --> Move & Rename
　　mv Test Test1 --> Rename folder

　　8) Command Name: rmdir
　　Command Derived From: remove directory
　　Command Path: /bin/rmdir
　　Command Permission: all users
　　Command Description: delete empty folder
　　Command Syntax: rmdir [source folder name]
　　Example:
　　rmdir Test --> It is only applied to empty folder. So its usage is highly restricted.
　　
　　9) Command Name: rm
　　Command Derived From: remove
　　Command Path: /bin/rm
　　Command Permission: all users
　　Command Description: delete file or folder
　　Command Syntax: rm  -r [source folder name or source file name]  -> When we remove some files, there may be a prompt that ask for confirmation.
　　-f [source folder name or source file name]  -> Mean 'force delete', there is no prompt for confirmation. It benefits the automatic scription.
　　Example:
　　rm Test.java  --> Delete single file
　　rm -r Test1    --> Delete folder that may not be empty. But there may be prompts for every single file inside this folder asking for confirmation which is annonying.
　　rm -rf Test1   --> Delete folder that may not be empty.

　　P.S
　　1) The minimum store unit in Linux is data block with the size of 512Byte.
　　But we can customize the data block size.