Directory of review documents

Posted by fil on Sat, 05 Feb 2022 04:42:56 +0100

1.touch command: used to modify or the time attribute of the directory, including access time and change time. If the file does not exist, the system will create a new file.

Syntax:

touch [-acfm] [-d<Date time>] [-r<Reference documents or directories>] [-t<Date time>] [--help]

Parameter Description:

a: Change the reading time record of the file (atime and ctime)

m: Change the modification time record of the file (mtime and ctime)

d: Set the time and date in a variety of formats

t: Set the file time record in the same format as the date instruction

Example: create a new file

[root@centos7 data]# ls
[root@centos7 data]# touch file
[root@centos7 data]# ls
file
[root@centos7 data]# stat file
  File: 'file'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 803h/2051d      Inode: 67          Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Context: unconfined_u:object_r:default_t:s0
Access: 2022-02-05 09:18:19.259013812 +0800
Modify: 2022-02-05 09:18:19.259013812 +0800
Change: 2022-02-05 09:18:19.259013812 +0800
 Birth: -

 

 

2. Check the file type with file

[root@centos7 data]# file file
file: empty
[root@centos7 data]# file file1
file: ASCII text

 

 

3. File naming rules:

1) The maximum length of a file name is 255 bytes

2) The maximum length of file name including path is 4095 bytes

3) Blue - > directory green - > executable red - > compressed file light blue - > linked file gray - > other files

4) All characters are valid except / and NUL, but directory names and files using special characters are not recommended. Some characters need to be quoted in quotation marks

 

 

4. Change the suffix color of the document

/etc/DIR_COLORS

 

 

5.1) generate a file named $abc

[root@centos7 data]# touch '$abc'
[root@centos7 data]# ll $abc
total 4
-rw-r--r--. 1 root root  0 Feb  5 09:31 $abc

Note: single quotation marks should be used here, not double quotation marks, because double quotation marks will recognize $, and abc will be regarded as a variable, and this variable is undefined, so touch will find a file with an empty name by default

[root@centos7 data]# touch "$abc"
touch: cannot touch '': No such file or directory

Similarly, deletion is the same

[root@centos7 data]# rm -rf '$abc'
[root@centos7 data]# ls
file

2) Generate a file named - A with touch

It is assumed that - a is the parameter of touch, so the following situation will occur

[root@centos7 data]# touch -a
touch: missing file operand
Try 'touch --help' for more information.

Therefore, we need to change our thinking and use -- add a space to indicate that there is no parameter:

[root@centos7 data]# touch -- -a
[root@centos7 data]# ls
-a  file

Of course, delete it. Similarly:

[root@centos7 data]# rm -rf -- -a
[root@centos7 data]# ls
file

 

 

6. File types under Linux

1) - ordinary documents

2) d directory file

3) Block b equipment

4) c character device

5) l symbolic link file

6) p pipe file (pipe)

7) s socket file (socket)

 

 

7. Display current working directory

1) Each SHELL and system process has a current working directory

2)CWD: current work direcctory

3) Displays the absolute path of the current SHELL CWD

pwd(printing working directory):

-P shows the real physical path - L shows the link path (default)

[root@centos7 dir1]# pwd -P    
/data/dir1
[root@centos7 dir1]# pwd -L    
/data/dir1

 

 

8. View file status

1)stat

2) Three timestamps:

Access time: access time, atime, to read the contents of the file

Modify time: modify time, mtime, change file content (data)

Change time: change time, ctime and metadata

[root@centos7 dir1]# stat /data/dir1
  File: '/data/dir1'
  Size: 6               Blocks: 0          IO Block: 4096   directory
Device: 803h/2051d      Inode: 67          Links: 2
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Context: unconfined_u:object_r:default_t:s0
Access: 2022-02-05 09:57:53.018038076 +0800
Modify: 2022-02-05 09:57:53.018038076 +0800
Change: 2022-02-05 09:57:53.018038076 +0800
 Birth: -

 

 

9. Absolute and relative paths

1) Absolute path: start with a forward slash and complete the location path of the file. It can be used whenever you want to specify a file name

2) Relative path: do not start with a slash. Specify the location relative to the current working directory or a directory. You can specify a file name as a short form

3)basename

[root@centos7 ~]# basename /etc/lvm/cache
cache

4)dirname

[root@centos7 ~]# dirname /etc/lvm/cache    
/etc/lvm

 

 

10 change directory

1) cd (change directory):

Use absolute or relative paths:

[root@centos7 ~]# cd /etc/lvm/cache
[root@centos7 cache]# 
[root@centos7 ~]# cd ../etc/lvm/cache
[root@centos7 cache]# 

Switch to parent directory

[root@centos7 etc]# cd ..
[root@centos7 /]# cd ..
[root@centos7 /]# pwd
/
[root@centos7 /]# cd ../..
[root@centos7 /]# pwd
/

Switch current user home directory

[root@centos7 /]# cd
[root@centos7 ~]# pwd
/root

Switch to previous working directory

[root@centos7 ~]# cd -
/
[root@centos7 /]# pwd
/

2) Option - P

3) Relevant environment variables:

PWD: current working path

[root@centos7 /]# echo $PWD
/

OLDPWD: last directory path

[root@centos7 /]# echo $OLDPWD
/root

 

 

11. List the contents ls

1) List the contents of the current directory or specify a directory

2) Usage:

ls [OPTIONS] [FILE_OR_DIRS]

3) Example:

ls -a contains hidden files

[root@centos7 ~]# ls -a
.              .bash_profile   .cache   Desktop    .esd_auth      .mozilla  Public     .viminfo
..             .bash_profiley  .config  Documents  .ICEauthority  Music     Templates  y
.bash_history  .bashrc         .dbus    Downloads  .local         Pictures  Videos

ls -l displays additional information

[root@centos7 ~]# ls -l
total 4
drwxr-xr-x. 2 root root   6 Feb  3 21:00 Desktop
drwxr-xr-x. 2 root root   6 Jan  1 01:28 Documents
drwxr-xr-x. 2 root root   6 Jan  1 01:28 Downloads
drwxr-xr-x. 2 root root   6 Jan  1 01:28 Music
drwxr-xr-x. 2 root root   6 Jan  1 01:28 Pictures
drwxr-xr-x. 2 root root   6 Jan  1 01:28 Public
drwxr-xr-x. 2 root root   6 Jan  1 01:28 Templates
drwxr-xr-x. 2 root root   6 Jan  1 01:28 Videos
-rw-r--r--. 1 root root 178 Feb  3 21:31 y

ls -R directory recursion

[root@centos7 data]# ls -R
.:
dir1

./dir1:
f1

ls -ld directory and symbolic link information

[root@centos7 ~]# ls -ld
dr-xr-x---. 15 root root 4096 Feb  5 09:22 .

ls -1 file line display

[root@centos7 ~]# ls -1
Desktop
Documents
Downloads
Music
Pictures
Public
Templates
Videos

ls -S files are sorted from large to small

[root@centos7 ~]# ls -S
y  Desktop  Documents  Downloads  Music  Pictures  Public  Templates  Videos

ls -t files sorted by mtime

[root@centos7 ~]# ls -t
y  Desktop  Documents  Downloads  Music  Pictures  Public  Templates  Videos

ls -u with - t option, display and sort by atime, from new to old

[root@centos7 ~]# ls -ut
Desktop  Documents  Downloads  Music  Pictures  Public  Templates  Videos  y

ls -U display by directory storage order

[root@centos7 ~]# ls -U
Desktop  Downloads  Templates  Public  Documents  Music  Pictures  Videos  y

ls -X sort by file suffix

[root@centos7 ~]# ls -X
Desktop  Documents  Downloads  Music  Pictures  Public  Templates  Videos  y

 

 

12.df command: the command is used to display the current file system disk usage on Linux system

Syntax:

df [option] ... [file]
[root@centos7 ~]# df
Filesystem     1K-blocks    Used Available Use% Mounted on
devtmpfs          915780       0    915780   0% /dev
tmpfs             931512       0    931512   0% /dev/shm
tmpfs             931512   10640    920872   2% /run
tmpfs             931512       0    931512   0% /sys/fs/cgroup
/dev/sda2       52403200 5029468  47373732  10% /
/dev/sda3       31441920   33024  31408896   1% /data
/dev/sda1        1038336  184100    854236  18% /boot
tmpfs             186304      32    186272   1% /run/user/0
/dev/sr0         9961428 9961428         0 100% /run/media/root/CentOS 7 x86_64

 

 

13. Shortcut key of bash (understand)

1) ctrl + l clear the screen, which is equivalent to the clear command

2) ctrl + o executes the current command and redisplays the command

3) ctrl + s block screen output, lock

4) ctrl + q allow screen entry

5) ctrl + c terminate command

6) ctrl + z suspend command

7) ctrl + a cursor moves to the beginning of the command line, which is equivalent to the Home key

8) ctrl + e cursor moves to the End of the command line, which is equivalent to the End key

9) ctrl + f cursor moves one character to the right

10) ctrl + b move the cursor one character to the left

11) alt + f cursor moves one word end to the right

12) alt + b moves the cursor one word to the left

13) alt + r deletes the entire current row

14) ctrl + xx cursor moves between the beginning of the command line and the cursor

15) ctrl + u deletes from the cursor to the beginning of the command line

16) ctrl + k deletes from the cursor to the end of the command line

17) ctrl + w delete from the cursor to the left to the beginning of the word

18) ctrl + d deletes a character at the cursor

19) alt + d is deleted from the cursor to the end of the word

20) ctrl + h deletes a character in front of the cursor

21) ctrl + y paste the deleted character behind the cursor

22) alt + c changes the initial capitalized word from the cursor to the right

23) alt + u start at the cursor and change the word on the right to uppercase

24) alt + l # start at the cursor and change the word on the right to lowercase

25) ctrl + t exchanges the position of the cursor and the previous character

26) alt + t , exchange the position of the cursor and the previous word

27) alt + N prompts to enter the specified character, and then repeat the character N times

Note: alt combination shortcut often conflicts with other software