Use of SED tools and regular expressions (Shell fourth day)

Sed tool "streaming editor"

--Non-interactive, filter based on pattern matching and modify text
--progressive processing and output of the results to the screen
--can achieve the output of the text, delete, replace, copy, cut, import, export and other operations

Command format:
1) Pre-command | sed [options] ' conditional directives ' "using pipelines"
2) SED [option] ' conditional directive ' file: ..

Common options:
-N Masks the default output, and the default SED outputs the entire contents of the read document

-I sed directly modifies the source file, the default SED only temporarily modifies the file through memory, the source file has no effect
[Normally, the SED command does the processing by outputting the results of the operation (including printing, deleting, etc.) to the current terminal screen without making any changes to the original file]

-R (Allow SED to support extended regular)

Cases:
-N
View File/etc/hosts line 1th
[Email protected] ~]# sed-n ' 1p '/etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4

View/etc/passwd 3-6 rows
[Email protected] ~]# sed-n ' 3,6p '/etc/passwd
Daemon:x:2:2:daemon:/sbin:/sbin/nologin
Adm:x:3:4:adm:/var/adm:/sbin/nologin
Lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
Sync:x:5:0:sync:/sbin:/bin/sync

View files/etc/passwd lines 3rd and 6th
[Email protected] ~]# sed-n ' 3p;6p '/etc/passwd
Daemon:x:2:2:daemon:/sbin:/sbin/nologin
Sync:x:5:0:sync:/sbin:/bin/sync

-I.
Delete files for deletion "actually no modification to files"
[[Email protected] ~]# sed ' d '/wooo.txt
[Email protected] ~]# Cat/wooo.txt
Thekncxn;zcnk
Dagahao the
Wojiaozazahuithe KOA
Modify source file "use with caution"
[Email protected] ~]# sed-i ' d '/wooo.txt
[Email protected] ~]# Cat/wooo.txt

II) Understanding the conditions of the SED tool

sed [options] ' conditional directives ' file: ..

1) SED commands can be conditionally matched using line numbers or regular:

Sed-n ' 3p '/etc/passwd print line 3rd

Sed-n ' 3,5p '/etc/passwd print line 3rd to 5th

Sed-n ' 3p;5p '/etc/passwd print lines 3rd and 5

Sed-n ' 3,+10p '/etc/passwd print 3rd and subsequent 10 lines

Sed-n ' 1~2p '/etc/passwd print odd lines

Sed-n ' 2~2p '/etc/passwd print even lines

2) Regular case

"Use//To find out what you need to search for"
Sed-n '/root/p '/etc/passwd print the row containing the root

Sed-n '/bash$/p '/etc/passwd print the line at the end of bash [user who can log in]

III) instruction set

"Print" p
Sed-n ' P ' a.txt output all lines, equivalent to cat a.txt
Sed-n ' 4p ' a.txt output line 4th
Sed-n ' 4,7p ' a.txt output line 4th to 7th
Sed-n ' 4,+10p ' a.txt output line 4th and the following 10 lines
Sed-n '/^bin/p ' a.txt output rows beginning with Bin
Sed-n ' $= ' a.txt the number of rows in the output file

[Email protected] ~]# sed-n ' $= '/etc/passwd
47 [No Back directory display]

[Email protected] ~]# wc-l/etc/passwd
47/etc/passwd

"Delete" D Note: Practice without the need to add I, to prevent accidental deletion of files!

Sed ' 3,5d ' a.txt Delete line 3rd to 5th
Sed '/xml/d ' a.txt delete all rows that contain XML
Sed '/xml/!d ' a.txt delete lines that do not contain XML! The symbol represents the inverse
Sed '/^install/d ' a.txt delete line starting with install
Sed ' $d ' a.txt delete the last line of a file
Sed '/^$/d ' a.txt Delete all empty lines

"Replace" s (s/old content/new content/Options)

Vim Test.txt Practice Environment
2017 2011 2018
2017 2017 2024
2017 2017 2017

Sed ' s/2017/xxxx/' test.txt replaces all rows matching the first 2017
Sed ' s/2017/xxxx/g ' test.txt replaces all 2017
Sed ' S/2017/XXXX/2 ' test.txt replaces all rows matching the second 2017
Sed ' s/2017//2 ' test.txt to delete all rows matching the second 2017
Sed ' 2S/2017/XXX/2 ' test.txt the second row matching the second 2017 delete
Sed ' 2~2s/2017/xxx/g ' test.txt replaces 2017 of even rows
Sed-n ' S/2017/x[[email protected] ~]# vim anonftp.shxxx/p ' test.txt print
Sed ' 4,7s/^/#/' a.txt//Comment out line 4th to 7th (beginning with #)
Sed ' s/^ #an/an/' a.txt//dismiss the comment of the line beginning with the #an (remove the # from the beginning)

Ifconfig | Sed-n ' 2s/netm. //p ' | sed ' s/. t//' View IP
172.25.0.11

Sed ' s/\/bin\/bash/\sbin\/sh/'/etc/passwd

Sed ' s#/bin/bash#/sbin/sh/# '/etc/passwd

Swap the first letter with the tail letter
Sed-r ' s/^ (.) (.*) (.) $/\3\2\1/'/wooo.txt
"Each line of text is split into" 1th character "," all characters in the middle "," last 1th character "three parts, and then rearrange the order to" 3-2-1 "by replacing the operation

Dello Worlh
OA GA had
Io xi za za huw

Enlarge all UPPERCASE Brackets
Sed-r ' s/([A-z])/[\1]/'/wooo.txt
Hell[o] World
D[a] Ga Hao
[W]o xi za za hui

Scripting: "Implementing automatic installation of FTP packages and configuring others to access and upload"
Installing the VSFTPD package with Yum
Modify the VSFTPD service configuration to turn on anonymous uploads
Adjust/var/ftp/pub directory permissions to allow FTP write
Start the VSFTPD service and set the boot from run

#!/bin/bash
Yum-y Install VSFTPD
Cp/etc/vsftpd/vsftpd.conf{,.back}
Sed-i ' s/^ #an/an/'/etc/vsftpd/vsftpd.conf
chmod 777/var/ftp/pub
Systemctl Restart VSFTPD
Systemctl Enable VSFTPD

Unable to access common causes
1) firewall is not open
2) SELinux not open
3) Restart Service

sed [option] ' conditional directive ' file .....
Option:-n-i-R
Condition: line number,/regular/
directive: P,d,s,a,i,c

A,append Append, after
I,insert INSERT, Front
C, delete and insert the row

: R Read in
: W Save As
Sed ' 2r/etc/hosts ' tmp.txt reads the file tmp.txt into the second line of the file/etc/hosts
Sed ' w/root/b.txt ' tmp.txt save file Tmp.txt as file Root/b.txt inside
Sed ' 2w/root/b.txt ' tmp.txt will

Script: Filter users and display passwords
#!/bin/bash
A=sed -n /bash$/s/:.*//p /etc/passwd
For I in $a
Do
pass=grep $i /etc/shadow
pass1=${pass#:}
pass2=${pass1%%:}
echo "$i------> $pass 2"
Done

Use of SED tools and regular expressions (Shell fourth day)