1. File operation

• touch command
  • Create a file. If the file name does not exist, create it directly. If it exists, change the access time
  • touch [option] filename1 filename2...

root@ubuntu:~/Test# touch hello.c
root@ubuntu:~/Test# ls
hello.c

• rm command: delete file or directory

  • Parameter - r recursively delete subdirectories
  • rm -rf * delete all contents in the current directory (mandatory deletion, use with caution)

• cp and mv commands, equivalent to Windows platform copy and cut

  • cp [option] srcpath despath
  • Despath is a directory. Copy srcpath to the despath directory
  • Despath is not a directory. Create a XXX file under... / in the superior directory (... / xxx) of despath, and copy the contents of srcpath

• cat command

  • Cat file name: display file information directly to the screen

• more and less, display file information by screen

  • more:

    • Enter line by line
    • Space, page by page display

  • less:

    • Enter or up and down arrow keys can repeatedly view the contents of the file

• head and tail commands

  • head view file header, default display 10 lines of content
    • head -n the number of rows that can be specified
  • tail view the end of the file, default display 10 lines of content
    • -n can specify a function
    • -f can trace the end of the file

2. Statistical information related

• wc command: the English word is word cout, which is the content of the statistics file
  • -l) display line
  • -w word
  • -c bytes

root@ubuntu:~/Test# wc hello.c 
 8 10 91 hello.c
root@ubuntu:~/Test# wc -l hello.c 
8 hello.c
root@ubuntu:~/Test# wc -w hello.c 
10 hello.c
root@ubuntu:~/Test# wc -c hello.c 
91 hello.c

• df displays disk space information

root@ubuntu:~# df -h 
//File system capacity used% mount points available
udev            973M     0  973M    0% /dev
tmpfs           199M  9.0M  190M    5% /run
/dev/sda1        21G  9.2G   11G   48% /
tmpfs           992M  256K  992M    1% /dev/shm
tmpfs           5.0M  4.0K  5.0M    1% /run/lock
tmpfs           992M     0  992M    0% /sys/fs/cgroup
tmpfs           199M   60K  199M    1% /run/user/1000

3. File permissions and user attributes

• Explain the corresponding fields

root@ubuntu:~/Test# ls -l
//Total dosage 4
-rw-r--r-- 1 root root 91 10 Month 27 14:16 hello.c

• -Represents the file type and d represents the directory file

• rw - the permission of the user who has read and write permission

• The group has read only permissions

• r -- other user permissions, which are also readable only

• We can also use octal digits to represent permission bits

  • rw - --- > 110 --- > 6 user bits
  • r -- - > 100 -- > 4 group permission bits
  • r -- - > 100 -- > 4 other permission bits
  • Finally, they are combined 0664

• Oh, by the way, there is also a 1, which represents the count of hard links. There will be a command to demonstrate below

• Create hard link - ln src des

root@ubuntu:~/Test# ln hello.c hello.c.hard
root@ubuntu:~/Test# ls
hello.c  hello.c.hard
root@ubuntu:~/Test# ln hello.c hello.c.hard1
root@ubuntu:~/Test# ls -l
//Total dosage 12
-rw-r--r-- 3 root root 91 10 27 14:16 hello.c
-rw-r--r-- 3 root root 91 10 27 14:16 hello.c.hard
-rw-r--r-- 3 root root 91 10 27 14:16 hello.c.hard1

At this point, the hard link count changes to 3. When our hard link count changes to 0, the file will also be deleted

• Create a soft link -- ln -s file or directory

root@ubuntu:~/Test# ln -s hello.c hello.c.soft
root@ubuntu:~/Test# ls -l
//Total dosage 12
-rw-r--r-- 3 root root 91 10 Month 27 14:16 hello.c
-rw-r--r-- 3 root root 91 10 Month 27 14:16 hello.c.hard
-rw-r--r-- 3 root root 91 10 Month 27 14:16 hello.c.hard1
lrwxrwxrwx 1 root root  7 10 Month 27 14:43 hello.c.soft -> hello.c

• Remove soft and hard links: unlink

4. Change document authority

• chmod command

  • chmod [u|g|o|a] [+|-][r|w|x] filename
  • Change the file permission in numerical way, for example: chmod 0664 main.c

• chown and chgrp change users and change groups

  • If the current user is not root, you need to use the administrator to modify the file ownership
  • chown user: Group filename | directory
  • chgrp group filename directory