Detailed explanation of system input and output management in Linux

Management of input and output in the system

1. Understand the input and output of the system

In Linux system, 1 indicates correct output and 2 indicates incorrect output

2. Manage input and output symbols

(1) Output redirection (output to a specified location)

> ## Redirect correct output 2> ## Redirect error output &> ## Redirect all output

Note: The following experiments should be completed among ordinary users

find /etc/ -name passwd > file1 ##Direct correct output to file1 (wrong output that is not put into the file will be displayed)
find /etc/ -name passwd 2> file2 ##Direct error output to file2 (will display correct output that was not put into the file)
find /etc/ -name passwd &> file3 ##Direct all output to file3 

file ##Clear file (because the '>' symbol will overwrite the source file when it is output, so > file will overwrite the source file with a blank space to achieve the effect of clearing)

(2) Output append

>> ##Append correct output to the end of the file 2>> ##Append error output to the end of the file&>> ##Append all output to the end of the file

Note: Appending will not overwrite the original file contents

(3) Input redirection

<<EOF

content

EOF (EOF here can be any combination, but it needs to be the same before and after)

for example:

vim file
Enter passwd student<<EOF
heihei
heihei
EOF

Command line input file ##Modify student user password

3. Pipeline

Function: turns the output of the previous command into the input of the next command in the pipeline

Note: The pipeline only allows correct output to pass. If you want incorrect output, you should use 2>&1 to convert the incorrect output number into the correct output number before outputting it.

| ##Turn the correct output of the first command into the input of the second command after the pipeline 2>&1 ##Turn the error output numbered 2 into the correct output numbered 1 tee ##Copy the output to the specified location For example: ls /bin |wc -l ##Count how many files there are in /bin find /etc/ -name passwd 2>&1 | wc -l ##Turn the error output numbered 2 into the correct output numbered 1 and count the number find/etc/ -name passwd 2>&1 | tee file |wc -l ##Turn the error output numbered 2 into the correct output numbered 1 and put them into the file file and count the number 

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