[EE485] March 15th Class - Linux & Shell

what is a shell?
Gets command from the user and runs the command on OS.

1. sudo, su, and man
   $sudo [command]: Superuser-do: runs a command as root
   ex) $sudo shutdown -h now
   : Runs 'shutdown -h now' as root, asks for the root password before running the commnand.

$su [user-to-be-switched-to]

$man [command]: shows the manual of command
ex) $man sudo

2. Directory Layout, and commands related to directories/files

In the highest, root directory. (This is not the same with root access.)

$ls: list directory contents

$cd [dir]: switches the current directory to [dir]
If [dir] is missing, it goes to your home directory.

ex) $cd ./temp

$pwd: Displays the present working directory name (present working directory)

$cat [files]: concatenates and displays files

$mkdir [dir]$rmdir [dir] :create/remove [dir]

$rm [files]: remove files

$rm -r

$mv [A][B]: Move file A to file B (rename and/or relocate A)
ex) $mv a.txt ~/tmp/ //relocate a.txt to b.txt
$mv a.txt b.txt //rename a.txt to b.txt
$mv a.txt ~/tmp/b.txt //rename and relocate a.txt
$mv ./tmp tmp2 //rename a directoty,

cf) ~/ : home directory
./ : current directory

3. Miscellaneous & Environment Variables

$echo [argument]: displays arguements to the screen$exit/logout/ctrl-d: exits the shell or your current session
$clear: clears the screen

What is Environment Variables?
$PATH ???$HOME ???

4. which and -h option
   which [command]: displays the location of command
   $which ls //output: /bin/ls$which which //output: /usr/bin/which

Hints: -h option
[command] -h

5. Working with Directories
   Special Directory
   . : this directory
   ..: Parent directory

• : previous directory

6. How to Execute a Program in Current Directory?
   You should specify the directory
   $program //doesn't work$./program //GOOD!

7. Creating/Removing Directories
   $mkdir/rmdir -p dir: creates/removes all intermediate directories in dir

ex) $mkdir newdir //works
$mkdir newdir/product/reviews //mkdir: cannot create directory
$mkdir -p newdir/product/reviews //works
$rmdir newdir //rmdir: failed to remove 'newdir': Directory not empty
$rm -rf newdir //works, -f means 'force'

8. Listing Files with ls
   $ls : just listing$ls -l: Gives whole bunch of things together.

other options
-a: all files including hidden files
-t: sort by modified time
-d: displays only directory names not their contents
-R: list files recursively

9. File permission
   10 characters.

first character: file type
'-' regular type
'd' directory
'l' symbolic link (pointer file)
Permissions:
r: readable
w: writable
x: executable
Groups:
u: user텍스트
g: group
o: other