I/O and pipelines under Linux

Read Catalogue

• 1. Standard input and output

• 2. Input and output redirection

• 3.tr command

• 4. Piping and Tee

• 5. Practice

  
  

  
  

1. Standard input and output

(1) Linux provides three kinds of I/O devices to the program

Standard input: (STDIN)-0 accepts input from the keyboard by default

Standard output: (STDOUT)-1 Default output to terminal window

Standard error: (Stdeer)-2 default output to terminal window

(2) Input device: keyboard, mouse, scanner, camera, etc.

Output devices are: printers, monitors, projectors, etc.

2. Input/Output redirection

Correct output

2〉 Error Output

&〉 full output (overwrite redirect)

> file content will be overwritten

SET-C: Prevents overwriting of existing files, but can append

>| File: Force overwrite

Set +C allows overwriting

>> additional content based on the original content

The file does not exist when,> and >> can create a new file, the file already exists > represents an overlay,>> represents an append

2>&1 turns the wrong result into the right result

1>&2 turn the right result into the wrong result

(): Merging stdout of multiple programs

Cal 2007;cal 2008

(Cal; cal) >all.txt

** 3, tr command   

TR Convert and delete characters

TR [OPTION] .... Set1[set2]

Options:

-c-c--complement: Taking the complement of the character set

-D--delete: Delete all characters belonging to the first character set

- s--squeeze-repeats: repeats consecutive characters in a single character

- t--truncate-set1: Converts the first character set corresponding character to the character corresponding to the second character set

import STDIN from a file

(1) Use < to redirect standard input

(2) Some commands can accept STDIN imported from a file

Tr'A- z' 'A- z'</etc/issue This command converts lowercase characters in /etc/issue to uppercase characters

(3) tr-d ABC </etc/fstab Delete all any character in the 11>ABC

(4) Cat > file

Mage

Wangxiaochun

Press Ctrl+d to leave, you can use the file instead of the keyboard input

Use "<< stop words" to redirect multiple lines to STDIN

4. Piping and Tee

use symbols "| "indicates that the command used to connect

Command 1 | Command 2 | Command 3 ...

The ability to combine multiple tools:

ls | Tr ' A-Z ' A-Z

Less: A page-by-page view input ls-l/etc | Less

Mail: Email Send input echo "Test Email" | Mail-s "Test" [email protected]

Tee: Read from standard input, write to standard output, and save to file

5. Practice

1. Calculation 1+2+3+. The sum of +99+100

echo 1+2|bc echo {1..100} echo {1...100} |tr "" +|bc

2, a Linux user to the root email, request the message titled "Help", the message body is as follows: Hello, I am user name, the system version is Here,please help me to check it, Thanks operating system version information

echo-e hello,i am ' whoami ', the system version is Here,please help me to check it,thanks. " \ n "' Cat/etc/redhat-release ' | Mail-s Help Root

3. Convert the current system login user's information to uppercase and save to the/tmp/who.out file
Who | tr [A-z] [a-z] >/tmp/who.out

4. Convert the contents of the/etc/issue file to uppercase and save to the/tmp/issue.out file

cat/etc/issue |tr A-z >/tmp/issue.out

6, processing string "Xt.,l 1 jr#! $mn 2 c*/fe 3 uz 4", keep only the numbers and spaces

echo "Xt.,l 1 jr#hat-releasemn 2 c*/fe 3 uz 4" | tr-cd [:d igit:][:blank:]

7. Display the path variable in a separate row for each directory

echo $PATH |tr: "\ n"

I/O and pipelines under Linux