1.Linux under changes (current user) environment variable: After entering vim ~ / .profile entered in the terminal, add the last line PATH = "-----------------: $ PATH ", enter the file name directly after adding -> enter
Add environment variables to all users: / etc / profile, add the last line PATH = "-----------------: $ PATH", enter the file name directly after the addition of - > Enter
2. Check the environment variable: env
3.export PATH="--------------:$PATH"
export AA="star"
echo $star
(The above command will be executed) echo
4.echo wrap
echo -n does not wrap == printf (default not wrap)
5 pipe character: cat -n qq.py | qq.py -rn | wc -l
Output: 3
6. Redirection:>
（1）> ww.txt
cat ww.txt file was empty
(2)> qw.txt empty if file exists, if the file does not exist, create
(3) additional content, echo to qw.txt inside "to child star, refuel" >> qw.txt
echo itself has a wrap
Right 7. Standard Output: 1>
(1) to write files to qw.txt qq.py in ------> cat qq.py 1> qw.txt
(2) the file is added to qw.txt qq.py in ------> cat qq.py 1 >> qw.txt
8. The standard error output: 2>
(1)cat asdf 2> qw
Because there is no qw this file, so the error message qw, cat qw qw see an error message will be displayed
9. The right standard error output ------> cat asdf &> qw
cat qq.py 1> qw 2> ww
cat qq.py 1 >> qw 2 >> ww two documents will be displayed
>: File overwrites
>>: Append files