Use of common commands for Linux systems

Common ways to use commands:

1.echo

Echo-display a line of text

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Get more precise command operation with manual help

Outputting a string to a display device

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Common options:

-N: No line break, 650) this.width=650; "src=" Https://s3.51cto.com/wyfs02/M01/08/65/wKiom1ngotbgW5yYAAAHU6zkT9I145.png "title = "3.png" alt= "Wkiom1ngotbgw5yyaaahu6zkt9i145.png"/>;

-e: The escape sequence that is booted with "\" takes effect

\ n: Line break

\ t: Horizontal tab

\v: Vertical tab

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Similar to the echo command is printf, is not limited by-e (in, only after the-e command takes effect, the following \ \, \a and other commands can take effect), you can directly \ n execute a line-break command, under echo other commands similar to, can be used directly, not affected by

-E Restrictions

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PS: To distinguish between a character and a variable name, generally add {} to distinguish between characters and variable names

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2.cd

Internal commands, using Help for more detailed assistance

Change the shell working directory.

Switch working directory

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CD:CD [-l|[ -P [-e]] [dir] indicates the part that can be omitted in parentheses;

Cd/path/to/somedir (the last parameter is the directory, otherwise it will be an error, because we are switching directories instead of files)

: Switches the working directory to the directory represented by the parameter;

Use CD directly: Switch working directory to the home directory of the currently logged in user, equivalent to CD ~;

cd-: Switch The working directory to the last working directory before this time;

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The shell provides two variables:

Pwd

Oldpwd

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Note: The method of getting variable values in the shell; Variable names are strictly case-sensitive;

Echo ${var_name}

{variable: The amount of memory space to assign}

cd~: Switch working directory to the home directory of the specified user

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To return to the home directory.

3.pwd

Print the name of the current working directory

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4.ls

Ls-list Directory Contents

Note: The contents of the directory are file names

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ls [OPTIONS] ... [FILE] ...

The bracket option can be omitted

In the Linux file system, all with "." The file with the starting character of the most file name is the hidden file;

ls command to view the directory display sorted by character table, vertical display, long options and short options are the same;

Common options:

-a,--all: Show all files, including hidden files 650) this.width=650; "Src=" https://s5.51cto.com/wyfs02/M01/08/66/                           Wkiom1ngrqjwc3kgaaag1zjxvkc531.png "title=" 8.png "alt=" Wkiom1ngrqjwc3kgaaag1zjxvkc531.png "/> ；

-a,--almost-all: Display except "." and ".." All files, including hidden files 650) this.width=650; "Src=" https://s1.51cto.com/wyfs02/M02/A7/1C/                                       Wkiol1ngregaoqt1aaahbpbycnc265.png "title=" 9.png "alt=" Wkiol1ngregaoqt1aaahbpbycnc265.png "/> ；

--color[=when]: Display file names in different colors

-d,-directory: Displays the directory itself, not the file name in the directory 650) this.width=650; "Src=" https://s1.51cto.com/wyfs02/M00/A7/1C/ Wkiol1ngrscawfmwaaag0fq2vmo788.png "title=" 10.png "alt=" Wkiol1ngrscawfmwaaag0fq2vmo788.png "/> instead of

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-h,--human-readable: Displays a more readable form when displaying the size of a file

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Typically used with the-l option, such as 650) this.width=650; "Src=" https://s5.51cto.com/wyfs02/M00/A7/1C/                                                    Wkiol1ngrfcslvxdaabtmzukikm769.png "title=" 12.png "alt=" Wkiol1ngrfcslvxdaabtmzukikm769.png "/> Will add some symbols after the file;

-L: Display detailed properties of a file using a long column table

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the format is interpreted as:

-RW-------. 1 root root 1876 September 17:48 anaconda-ks.cfg

-: Represents the file type;

RW--------: The file's permission bit settings;

.: Indicates whether the file has special attributes or extended attributes;

1: Indicates the number of times the file has been hard-linked;

Root (first): The owner of a file;

Root (second): The genus of a file;

1876: The size of the file, before using-h, the unit is byte;

September 17 17:48: One of the timestamp of the file, indicating the time of the last modification;

Anaconda-ks.cfg: File name

for device files:

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~]# ls-l/dev/sr0

Similar format:

BRW-RW----. 1 root cdrom 11,0 September 10:50/dev/sr0

11,0:major,minor

Major: The main device number that identifies the device type, and then determines what driver needs to be loaded;

Minor: The secondary device number that identifies the different devices in the same device type;

The device number is represented by default with a 8-bit binary, so the default device number range is 0~255;

-R,--Reverse: Reverse output 650) this.width=650; "Src=" https://s2.51cto.com/wyfs02/M02/08/66/ Wkiom1ngstrd1oweaaaszpia2bw004.png "title=" 15.png "alt=" Wkiom1ngstrd1oweaaaszpia2bw004.png "/>

-R,--Recursive: recursive display, if there is a subdirectory in the target directory, then recursively display the contents of the subdirectory, recursively go down 650) this.width=650; "Src=" https://s2.51cto.com/wyfs02/M01/A7/ 1c/wkiol1ngshudcvzhaaaq4rpngck764.png "title=" 16.png "alt=" Wkiol1ngshudcvzhaaaq4rpngck764.png "/>

Note The following commands are strictly forbidden in the server, 650) this.width=650; "Src=" https://s1.51cto.com/wyfs02/M01/08/66/ Wkiom1ngtcvjtndsaaaerewqema678.png "title=" 18.png "alt=" Wkiom1ngtcvjtndsaaaerewqema678.png "/>, and will traverse all subdirectories under the root directory

, the CPU and memory of the server are seriously consumed,

；

-Z,--Context: Display file's SELinux security context label 650) this.width=650; "Src=" https://s3.51cto.com/wyfs02/M01/08/66/ Wkiom1ngs17dnyhgaabzeih3jp0878.png "title=" 17.png "alt=" Wkiom1ngs17dnyhgaabzeih3jp0878.png "/>;

5.mkdir

Mkdir-make directories, create a new directory;

mkdir [OPTIONS] ... DIRECTORY ...

-p,--parents: When the parent directory is created, if its parent directory does not exist, it is created first;

-v,--verbose: Display a message for each directory created

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6.rm

(rmdir command can only delete empty directory, not very useful, now generally no one to use)

Rm-remove Files or directories

removing files or directories

RM [Options]]file ...

-F,--Force: Violence, forced deletion of 650) this.width=650; "Src=" https://s1.51cto.com/wyfs02/M00/A7/1D/ Wkiol1ngs2eq90ouaaakjs0oar0205.png "title=" 20.png "alt=" Wkiol1ngs2eq90ouaaakjs0oar0205.png "/> the directory cannot be deleted by default;

-r,-r,--Recursive: Recursively delete content in directories and directories

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Note that if you use a command that is very dangerous

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All files under the root directory will be deleted and the system will not be available, and the command in the virtual machine should take a snapshot in advance;

And on the real server do not make this command, the consequences can not be imagined, extremely dangerous.

Use of common commands for Linux systems