Rhcsa third day notes

Look at the catalog file ： ls

View the contents of the text file

cat Output the contents of the file to the terminal , View file contents （ positive sequence ）

-n View the contents of the file and display the label

tac Output the contents of the file to the terminal , View file contents （ Show in reverse order ）

more Generally, large files can be displayed in pages through the terminal window , Finally, all contents are output to the terminal to view and display

less Open reading , Pagination display , Exit needs to pass q

？ keyword perhaps / keyword

n Match keywords up

N Match keywords down

head View the first ten lines of information in the file

-n Specify the number of lines to display

-n 3

tail View the last ten lines of the file

-n 3

-f follow Append the contents of the display file ctrl+c

tail -f /var/log/messages

Text editing

1.nano

2.vi / vim *** Text editor

  

The last line of the terminal

Display a new file or file name with a few lines and characters or no information （ Execute convenient commands ）

--insert--- ( Edit file contents )

： Last row mode

Command mode ：

dd Deletes the line where the cursor is located

d+enter Delete the line where the cursor is located and the next line of the cursor

dG Delete the line where the cursor is located and all lines at the end of the document

dgg Delete the line where the cursor is located and all lines at the beginning of the document

d^ Delete the cursor to the beginning of the line , Does not contain cursor characters

d$ Delete cursor to end of line , Contains the character of the cursor

x Delete cursor character

G Jump to the end of the document

gg Jump to the beginning of the document

4G Jump to line four

^ Head of line

$ At the end of the line

yy Copy

4yy Copy a total of four lines starting from the cursor

cc shear

4cc Cut a total of four lines starting from the cursor

p Paste （ Paste on the next line of the cursor ）

u Undo to the left （ Return to the last editing status ）

ctrl+r redo （ Undo right , Return to the state of recent editing ）

Insertion mode ：

a Insert content after cursor

A The end of the line where the cursor is located

i Insert content in front of the cursor

I The beginning of the line where the cursor is located

o Enter insertion mode , Add content on the next line of the cursor

O Enter insertion mode , Add content on the line above the cursor

s Delete cursor character , Enter insertion mode

S Deletes the line where the cursor is located , Enter insertion mode

Last row mode ：

:q sign out

:q! Forced exit

:w preservation

:wq Save and exit == ZZ Command mode

:wq! Forced save exit

:10 Jump to line 10

:r FILENMAE Read the contents of the specified file to the next line of the cursor

:%s % Match symbol , Indicates that all rows are matched s Replace the command / Characters to replace / The replaced character / Replace the keywords that are matched for the first time in each line g Replace all matching keywords %s /0/1/g

:set nu According to the line Numbers

:set nonu Cancel the line Numbers

/ keyword Quickly match the content of the line where the keyword is located

:noh Unhighlight

vim -o /etc/passwd /etc/shadow Multiple files horizontally split the display content

-O /etc/passwd /etc/shadow Left and right split screen display of file content

ctrl+w+w

vim + /etc/passwd Open the file and enter the end of the document

3.">" or “>>” Realize file editing

echo Print command

#echo  this is test    ( Standard I / O commands )
this is test   

 

 

$ Reference variables

#name=zhangsan
#echo $name
zhangsan
${}
#echo  ${name}
zhangsan

 

$? A command on the exit code is displayed 0 success 1-255 Error status

[[email protected] ~]# echo ${name}
zhangsan
[[email protected] ~]# echo $?
0
[[email protected] ~]# haha
bash: haha: command not found...
Failed to search for file: Cannot update read-only repo
[[email protected] ~]# echo $?
127

 

| Pipe, （ Take the standard output of the previous command as the standard input of the following command ）--- Nameless pipe

 Displays the tenth line of a file 
#head /etc/passwd | tail -1   
eg: Show /etc/passwd file 20-25 The content of the line 

​

**p Identified pipeline file （ name pipes ）

 Turn on two terminals 
1 terminal ：
#mkfifo /p1
#echo 123 > /p1
2 terminal ：
#cat /p1
123

 

The three quotation marks are different

' Single quotation marks ' Strong citation , Do not recognize the special meaning of special characters in quotation marks echo '$PS1'

" Double quotes " Weak reference , Identify characters with special meaning , echo “$PS1” --- If it is a variable, there is a difference between single reference and double reference

\ The quotation marks Command substitutions == $()

[[email protected] /]# echo " All files in the root directory \`ls`"

 

">" Output redirector ( Write the output result of the previous command to the specified file )

echo   helloworld > FILE       take helloworld The output result is written to the specified file through the output redirection character , When the file does not exist, it will be created 

“>>” Append redirector

echo this is test >> FILENAME 

< Enter the redirector

cat   <  /etc/passwd
head  < /etc/passwd

4. File editing << Termination Terminator

[[email protected] /]# cat << EOF        View content , Match the terminator to end the input 
> this is test                       -- The standard input 
> EOF                                -- Match to terminator , End standard input 
this is test                         -- Output the contents of the previous standard input to the standard output 
​
---------------------------
[[email protected] /]# cat << EOF >  file2
> this is 1
> this is 2
> this is 3
> EOF
[[email protected] /]# cat file2
this is 1
this is 2
this is 3

 

File descriptor ：0 Document standard input character 1 standard （ correct ） Output descriptor 2 Error output descriptor

cat 0< /etc/passwd
cat fff  1> file      ==  cat fff > file
cat fff   2> file
cat fff &> file == cat fff  1> file 2> file  == cat fff 1> file 2>&1
cat fff 1> file 2> /dev/null

 

Commands related to file content processing ---( That's ok )

grep Text filter display command

Command format ： grep [-options...] keyword file name ...

#grep root /etc/passwd take /etc/passwd In file root Keyword line print display

-v Reverse filtration , Print and display lines without keywords

-o Show only the matching keywords

-c Displays the number of rows matching the keyword

-i Ignore case

-n Filter and display line numbers

-w Filter by word

-A 2 Display keywords and the next two lines of information

-B 2 Display keywords and the last two lines of information

-C 3 Display keywords and three lines of information

 Filter specified files /etc/passwd There will be... In the file nologin The line of the keyword is written to login file , And write in the order of the original file .           
[[email protected] /]# grep nologin /etc/passwd  > login
 Only the key information of one matching file is displayed 
[[email protected] /]# grep -v ^# /etc/login.defs  | grep -v ^$
 Judge /usr/bin Whether there is passwd Executable file 
[[email protected] /]# ll /usr/bin | grep -w passwd
-rwsr-xr-x. 1 root root       34512 Aug 12  2018 passwd

 

^ What does it start with ^q ^#

$ What does it end with a$

^$ Blank line

[] Define the value range , Any single character in this range [1-9] grep ^[0-9] FILENAME The beginning is 0-9 The line of any number shows

[^] ^ Take the opposite ^[^0-9] ^[!0-9]

cut Text content cutting command

-d Specify the delimiter of the file content

-f Specify the intercepted field

#cut -d : -f 1  /etc/passwd
[[email protected] /]# date |cut -d " " -f 6
2022

-c Specify character interception cut -c 1-3 /etc/passwd

wc Text statistics command That's ok Word book Number of bytes file name

-l Just count the lines

-w Just count the number of words

-c Count the number of bytes

-m Count characters

How many users are there in the current system

[[email protected] /]# echo There are users in the current system \wc -l /etc/passwd | cut -d " " -f 1 individual > file There are users in the current system 44 individual

sort Text sorting Sort by character by default

-n Display in ascending order of numerical value

-r Show in reverse order

-t Specify the separator

-k Specified field

-u unique duplicate removal ==sort a.txt | uniq

[[email protected] /]# sort -t : -k 3  -n /etc/passwd
 take /etc/passwd  The contents of the document are passed through ： Split sorts the third field and displays the contents of each line in ascending order 

uniq To repeat the order ( Repeat rows adjacent to each other )

-c Displays the number of times each line is repeated

-d Show only recurring lines

-D Show all rows that appear repeatedly

tr Character substitution

echo abcde | tr  -t   a   1
-c   Inverse selection 
echo abcde | tr -c abc  0    Take care of abc Replace characters other than with 0 character 
   abc00
-s     Replace consecutive repeated characters with a single character 
echo   aaaaabcd | tr -s a 1    Will be a continuous number of a Replace the character with a 1 character 
-d   Delete selected characters 
echo abcdef | tr -d abc