Introduction to basic commands under Linux (vii)

I. I/O redirection:

System settings

Default output device: Standard output, STDOUT, 1

Default input device: standard input, STDIN, 0

Standard error Output: STDERR, 2

Standard input: Keyboard

Standard output and Error output: Display

Redirect to change the source and destination of the data

1. Output redirection:

> overwrites the contents of the original file

>> Append Output

SET-C: Prohibit overwrite redirection for already existing files;

Force overwrite output, use >|

Set +c: Turn off the above features

2>: Redirect Error output

2>>: Append method

&>: Redirect standard output or error output to the same file

<: Input redirection

<<:here Document

Two. Piping

The output of the previous command, as input to the latter command

Usage: Command 1 | Command 2 | Command 3 | ...

1.echo "Luochen" | Tr ' A-Z ' A-Z

2.echo "Luochen" | passwd--stdin Root

3.cut-d:-f1/etc/passwd | Sort-n | Tr ' A-Z ' A-Z

4.ls/var | Tr ' A-Z ' A-Z

5.tee command obtains data from standard input and saves data to a file at the same time to standard output data

6.wc-l/etc/passwd | Cut-d '-f1

7.ls/usr/bin | Wc-l

Practice:

1, Statistics/usr/bin/Directory of the number of files

# Ls/usr/bin | Wc-l

2. Take out the shell of all the users on the current system, require that each shell be displayed only once, and be displayed sequentially

# cut-d:-f7/etc/passwd | Sort-u

3, thinking: How to display the content type of each file in the/var/log directory

# file ' Ls/var/log '

4. Remove the 6th line of the/etc/inittab file

# head-6/etc/inittab | Tail-1

5. Take out the user name and shell of the 9th user in the/etc/passwd file, display it to the screen and save it to the/tmp/users file.

# tail-9/ETC/PASSWD | head-1 | Cut-d:-f1,7 | Tee >/tmp/users

6. Display all files starting with PA in/etc directory and count them

# ls-d/etc/pa* | Wc-l

7, do not use a text editor, add alias Cls=clear a line of content to the current user's. bashrc file

# echo "Alias Cls=clear" >> ~/.BASHRC

This article is from "Luo Chen's blog" blog, please be sure to keep this source http://luochen2015.blog.51cto.com/9772274/1635498

Introduction to basic commands under Linux (vii)