Shulou(Shulou.com)06/02 Report--

/ dev/sda2 hard disk / dev/shm memory

1. Understand the input and output in the system

Instructions in shell programs-> cpu to generate operation results-> character devices

Input the instruction in the shell program, send it to cpu to calculate the result, and then send it to the character device to display.

two。 Symbols for managing input and output

Redirect correct output

2 >: reimagine error output

& >: redirect all output

Note:

Redirection overwrites the contents of the original file

Example: (to take a screenshot)

"Note: the following experiments must be completed under student users"

Find / etc/-name passwd > file directs the correct input to file

Find / etc/-name passwd 2 > file.err misdirected input to file.err

Find / etc/-name passwd & > file.all directs all inputs to file.all

Clear a file command: > file name

3. Pipeline action

1.wc command

Using the wc instruction, we can calculate the number of Byte, words, or columns of a file. If the file name is not specified, or if the file name is given as "-", the wc instruction will read data from the standard input device.

-c displays bytes or chars displays only bytes

-l displays the number of rows

-w shows the number of words

$wc file name: displays the number of lines, words and bytes of the file

$wc multiple files: count the information of three files

3.2. The role of pipes

The function of the "|" pipe is to change the output of the previous command into the input of the latter command.

So ls / bin/ | wc-l is 1588 but ls / bin/ | wc-l is 1 because there is only one line in 1588.

Note: the pipeline only allows the correct output to pass through

The input through the pipe will become input, and the output that becomes input will be processed by the second command. If you need to save the output, you need to copy an output. The command used is "tee".

This lab is operated under ordinary users:

Find / etc/-name passwd | wc-l will see a result of 2 because the error output cannot go through the pipe

Find / etc/-name passwd 2 > & 1 | wc-l will see 19 because the output numbered 2 is converted to numbered 1 by "2 > & 1".

Find / etc/-name passwd 2 > & 1 | tee file | wc-l saves an output to file in counting the number of lines

4.3. Input redirection

Cat > file

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.