202334426_김동은_lecture_note_5.md

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Department of AI,SW / 202334426 / 김동은 Descriptions of Linux CLI 2

Standard Output

• '>' after a command : create and save the output in a file
• Command 'cat' : displays the content of a text file.
• '>>' : appends output(already exists) / create and write to a new file(doesn't exist)

Standard Input

• '<' : redirect input

It is possible to mix "<" and ">" together in a single line!

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Pipelines "|"

Pipeline feeds output of previous command to input of 'next' command. ex) command1 | command2 | command3 ....

$ ls -lh | less

Press "q" : exit the screen.

$ ls | wc -l
7
$

"wc - l" : displays the number of files in the current directory.

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Expansion

$ echo my name is dongeun
my name is dongeun
$

"echo" : print the text after command 'echo'.

$ echo *

" echo * " : print the files that exist in the current directory. (same function as '-ls')

Tip : Bachslash bachslash: ignore line change (enter) to enter a long command in multiple lines.

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Permission

Files and directories have a permission assigned differently to owner, group, ohters.

-rwx rwx rwx

-> read with 3 letters at a time -> 'rwx' means: Read, Write, and Execution

• '-': File type

  '-': indicates regular file 'd': indicates directory

• 1st 'rwx': permissions for the file owner.

• 2nd 'rwx': permissions for the group owner of the file

• 3rd 'rwx': permissions for all other users.

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Changing Permissions

Use command "chmod" to change permissions.

[me@linuxbox me]$ chmod 600 some_file

"600" means 6 = 110 = rw- for owners (owners can read and write the file) 0 = 000 = - - - for group (group owner can't read, write, and execute the file.) 0 = 000 = - - - for others (all other users can't read, write, and execute the file.)

We can grant various permissions by combining three numbers using binary numbers.

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Superuser

A superuser has all system administation authority!

Put "Sudo" before the command to use superuser's authority.

[me@linuxbox me]$ sudo some_command

if you want use superuser's authority continuously, use "-i"

[me@linuxbox me]$ sudo -i

Type "exit" : get out of a superuser session.

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Shell Script

This is used to store commands in advance and execute them sequentially whenever necessary.

$ nano myscript.sh

ehco "Hello Shell Script!"

$ sh myscript.sh
Hello Shell Script!
$