Linux should learn this--command set 7 (Pipeline command)

1. Pipe command symbol "|" function is to use the standard output of the previous command as the standard input for the latter command, in the form: " command a| command B".

The command to find the restricted login user is: grep "/sbin/nologin"/etc/passwd

The command to count the number of lines of text is: Wc-l

The output value of the search order is passed to the statistic command, in fact, as long as the pipe Fu Jian in the middle can be:

grep "/sbin/nologin"/etc/passwd|wc-l

Appendix:

The pipe character command is entirely possible: command a| Command b| command C

2. View the home directory information:

ls/home/

To view information about the ZZZZZ directory:

LS zzzzz/

These two as if the command has been executed successfully, but in fact there is a difference, the former is returned by the standard output , the latter execution fails to return the error output .

Standard input (STDIN, file descriptor 0): The default is input from the keyboard, and 0 indicates the output from other files or commands.

Standard output (STDOUT, file descriptor 1): The default output to the screen, 1 indicates the file.

Error output (STDERR, file descriptor 2): The default output to the screen, 2 indicates the file.

There are these conditions for output redirects:

There are these conditions for the input redirection character:

Empty the original content data:

echo "Jacun" > Test.txt

Append to the original content:

echo "Jacun" >> test.txt

REDIRECT the Test.txt file as input to the wc-l command to calculate the number of rows:

Cat Test.txt | Wc-l

Equivalent to:

Wc-l < Test.txt

Linux should learn this--command set 7 (Pipeline command)