Linux Common Command Anatomy of learning notes-CAT/CHMOD/CD

1. Cat: Used to connect files and print to standard output devices. (Usage rights: all users)

Syntax format:cat [-abeensttuv] [--help] [--version] fileName

parameter Description:

-N or--number: Numbers the number of rows for all outputs starting from 1.

-B or--number-nonblank: Similar to-n, except that blank lines are not numbered.

-S or--squeeze-blank: a blank line that is substituted for a row when it encounters a blank line that has more than two consecutive lines.

-V or--show-nonprinting: Use the ^ and m symbols, except for LFD and TAB.

-E or--show-ends: Displays $ at the end of each line.

-T or--show-tabs: Displays the TAB character as ^i.

-e: Equivalent to-ve.

-A,--show-all: equivalent to-vet.

-E: Equivalent to "-ve" option;

-T: equivalent to the "-vt" option;

Example:

Cat-n text1.txt text2.txt > Text.txt//Add the contents of Text1 and Text2 to the text document after adding a line number to the document

Cat/dev/null > Test.txt//emptying Test.txt document contents

2, Chmod:linux/unix file call permissions are divided into three levels: file owners, groups, and other. The use of chmod can be used to control how files are called by others. (Usage rights: all users)

Syntax format:chmod [-CFVR] [--help] [--version] mode file ...

parameter Description

Mode: Permission set string, in the following format:

[Ugoa ...] [[+-=][rwxx] ...] [,...]

which

U represents the owner of the file, and G indicates that the owner of the file belongs to the same group (group), and O means the other person, and a means that all three are.

+ indicates an increase in permissions,-represents a cancellation permission, = Represents a unique set of permissions.

R means readable, w means writable, x is executable, x means only if the file is a subdirectory, or the file has been set to executable.

Additional parameter Description:

-C: If the file permission has changed, it will not show its change action

-F: Do not display an error message if the file permissions cannot be changed

-V: Show details of permission changes

-r: The same permissions change for all files in the current directory as subdirectories (that is, they are changed in a recursive manner)

--HELP: Show Auxiliary Instructions

--version: Display version

Example:

chmod Ugo+r file1. TXT//Set the file File1.txt to all people can read chmod a+r file1. TXT

　　chmod ug+w,o-w file1. TXT file2. TXT//Files File1.txt and File2.txt are set to the owner of the file, and the same group as the person to which they belong can be written, but not others

chmod u +x ex1. PY//ex1.py is set to only the owner of the file can perform

chmod -R a+r *//Set All files and subdirectories in the current directory to be readable by anyone

In addition chmod can also use numbers to represent permissions such as:

777 File

The syntax is:chmod ABC file ( where A,b,c is a number that represents the permissions of user, Group, and other respectively.) ）

R=4,w=2,x=1

• To rwx the attribute then 4+2+1=7;
• To rw-the attribute then 4+2=6;
• To r-x the property, 4+1=5.

chmod a=rwx file   and 777 file  have the same effect

chmod ug=rwx,o=x file       and 771 file  Same effect

3. CD: Used to switch the current working directory to DirName
Example:

cd /usr/bin//Jump to/usr/bin/

CD ~//Jump to your home directory

CD ..     /.. Jump to the top two of the current directory

Linux Common Command Anatomy of learning notes-CAT/CHMOD/CD