Linux Extended Regular Expressions

1. Extended Regular Expression 1.1 + (plus sign)

+ indicates that the previous character appears 1 or more times or more than 1 times

1.1.1 Understanding +

Requirements: Remove the file contents of the continuous occurrence of lowercase letters

[[email protected]/oldboy]#egrep ' 0+ ' oldboy.txt grep-e===egrepmy QQ is49000448 not4900000448. [[Email protected]-lnb/oldboy]#grep-e ' 0+ ' oldboy.txtmy QQ is49000448 not4900000448. [[Email protected]-lnb/oldboy]#grep ' 0\+ ' oldboy.txtmy QQ is49000448 not4900000448. [[Email protected]-50 Oldboy]#egrep ' [a-z]+ ' Oldboy.txtyou can use [a-z]+Show too much word content here do not paste [[email protected]-50 Oldboy]#egrep ' [a-z]+ ' Oldboy.txt-o-o display the lookup processAmoldboy##[] with + + will think [] inside is a whole so display as a character group

The difference between 1.1.2 Plus + and no plus +

[[email protected]/oldboy] # egrep ' 0+ ' oldboy.txt-o    Plus + sign together will show 00000000[[email protected]-lnb/oldboy]# egrep ' 0 ' oldboy.txt-o     no + + number alone display 00000000

View Code1.1 | or 1.1.1 Understanding |

[[email protected] Oldboy] #  egrep ' oldboy|linux ' oldboy.txt  find the contents of Oldboy or Linux in the file is HTTP  //Is http://blog.oldboyedu.com

1.1.2 | Usage of

Exclude # and Blank lines in a file

/etc/ssh/sshd_config exclude # and Blank lines in a file

[[email protected] ssh] # egrep-v ' ^$|# ' sshd_config

1.1 () (parentheses)

() represents a whole reverse reference/backward reference

Sed-r using the extended regular

Idea: Protect what you want ()

SED uses a \ Numeric reference between two well numbers after ' s## #g '

[[email protected] Oldboy]#egrep ' oldb (o|e) y ' oldboy.txt here means finding Oldboy and Oldbey[[Email protected]-50 Oldboy]#echo 123456|sed-r ' s# (. *) #\1#g '123456[[Email protected]-50 Oldboy]#echo 123456|sed-r ' s# (. *) #<\1> #g '<123456>Change 123456 to<34>56[[Email protected]-50 Oldboy]#echo 123456|sed-r ' s# (#<\1> #g ')12<34>56the dot represents any one character, and \2 represents the second parenthesis. [[Email protected]~]#echo 123456|sed-r ' s# (.). (..). (.) #\2#g '34

1.1 {} (curly braces)

The previous character has at least consecutive n times, with a maximum of M occurrences

Different methods of 1.1.1 curly braces

0{3,6}   >=3 <=60{3}     ==30{3,}    >=30{,6}    >=0 <=6

1.1.2 Application Method

[[email protected] Oldboy] # egrep ' [0-9x]{18} ' ID.txt     here means {} The preceding characters appear 18 times [[email protected]-lnb/oldboy]#  Egrep ' 0{3,4} ' oldboy.txt indicates that 0 appears with a minimum of 3 occurrences up to 4 times   is 49000448 not 4900000448 . [Email protected] -lnb/oldboy]#  egrep ' 0{3} ' oldboy.txt   means 0 has appeared 3 times   was 49000448 not 4900000448.

Usage of 1.1.3 {}

Remove the ID number from the file

[[email protected]/oldboy]#Cat ID.txtGold211324198705244720million500224197105168312ren 1231231231oldboy any 3oldboy ren lidao97303136098 ren alex2197303136098 ren 350182197303oldgir lv211282199209113038Hole150000198309176071Zou371001197412221284He130185200011215926du362522198711278101to 14052219961008852x[[email protected]-lnb/oldboy]#egrep ' [0-9x]{18} ' ID.txt#The expression 0 to 9 and X appeared altogether 18 times such that the lookup was inaccurate because a single number appeared 18 times can also be filtered outGold211324198705244720million500224197105168312LV211282199209113038Hole150000198309176071Zou371001197412221284He130185200011215926du362522198711278101xxxxxxxxxxxxxxxxxx to 14052219961008852x[[email protected]-lnb/oldboy]#egrep ' [0-9]{17}[0-9x] ' id.txt exact search but not the most accurateGold211324198705244720million500224197105168312LV211282199209113038Hole150000198309176071Zou371001197412221284He130185200011215926du362522198711278101to 14052219961008852X

View Code1.1? Question mark

？ The previous symbol appears consecutively 0 or 1 times with or without

？ The information represented by 0 or 1 times represents the same content as {0,1} is actually the same

1th Chapter Regular Expression Pit 1.1 Pit 1 grep ' 0* '

will show the contents of the file.

0* 0 times No grep will show the contents of the file.

0 times or more 0 00000000000

 [[email protected] ~]#   grep "0*" Clsn.txt Pit 1 grep ' 0* ' will display the contents of the file  i am clsn teacher! I Teach Linux. I like badminton ball, billiard ball  and   Chinese chess!my blog  is  http:// clsn.blog.51cto.com our site  is  http:// www.etiantian.org my qq num  is  49000448.  not  4900000448.my God, I am  not   Oldbey,but clsn![ [Email protected]  ~]#   Grep-o "0*" Clsn.txt  00000000 

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1.2 Pit 2 [Oldboy]

[Oldboy] looks for o l d b o y instead of Oldboy overall

[[email protected]/oldboy]#grep ' [Oldboy] ' Oldboy.txtWhat Oldboy find here is o l d b o y instead of Oldboy overall I am oldboy teacher! I Teach Linux. I like badminton ball, billiard Ball andChinese Chess!my Blog is/HTTPoldboy.blog.51cto.comour Size is/HTTPBlog.oldboyedu.commy QQ is49000448 not4900000448. My God, I am notoldbey,but oldboy! [[Email protected]-lnb/oldboy]#grep-o ' [Oldboy] ' oldboy.txt display the Find processoldboyllb

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1.3 Pit 3 [^#^$] [^$] [^#$]

[] in $. No special meaning similar to \ escape character

[[email protected]/oldboy]#cat Oldboy.txt viewing file contentsI am Oldboy teacher! I Teach Linux. I like badminton ball, billiard Ball andChinese chess!+++++\\\\\\!!!! $$$$$$^^^####!!! ^^ ^^ ^[email protected]@@@@####[[Email protected]-lnb/oldboy]#grep ' [^#^$] ' oldboy.txt here means to exclude #^$ equivalent to removing the special meaningI am Oldboy teacher! I Teach Linux. I like badminton ball, billiard Ball andChinese chess!+++++\\\\\\!!!! $$$$$$^^^####!!! ^^ ^^ ^[email protected]@@@@####[[Email protected]-lnb/oldboy]#grep ' \.$ ' oldboy.txt here means to find the end of the.I teach Linux. not4900000448. [[Email protected]-lnb/oldboy]#grep ' [.] $ ' oldboy.txt here also means to find the same as the. EndI teach Linux. not4900000448.

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1.4 Pit 4 grep-v with [^a-z]

[^a-z] excludes certain characters by character

Grep-v [A-z] excluding row by line

[[email protected]/oldboy] # grep ' [^a-z] '  oldboy.txt[[email protected]-lnb/oldboy]#  grep-v ' [A-z] '  Oldboy.txt

Linux Extended Regular Expressions