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Regular expression of rocky basis

2022-07-19 10:02:00 【51CTO】

Regular expressions

REGEXP： Regular Expressions, Patterns written by a special class of characters and text characters , Some of them are characters （ Metacharacters ） It doesn't mean the literal meaning of the character , And the function of control or configuration , Similar to the enhanced version of the wildcard function , But unlike wildcards , wildcard Function is used to handle file name , and Regular expressions Is dealing with text content character . Regular expressions are widely supported by many programs and development languages ：vim, less,grep,sed,awk, nginx,mysql etc.

There are two types of regular expressions ： Basic Regular Expression ：BRE Basic Regular Expressions Extended regular expression ：ERE Extended Regular Expressions

Metacharacter classification of regular expressions ： Character matching 、 Number of matches 、 Position anchoring 、 grouping

help ：man 7 regex

Basic regular expression metacharacters

Character matching

       
       .        Match any single character ( except \n), It can be a Chinese character or the characters of other countries 
       
[]       Match any single character in the specified range , Example ：[wang] [0-9] [a-z] [a-zA-Z]
       
[^]      Matches any single character outside the specified range , Example ：[^wang]
       
[:alnum:]  Letters and numbers 
       
[:alpha:]  Represents any English case character , or  A-Z, a-z
       
[:lower:]  Lowercase letters , Example :[[:lower:]], amount to [a-z]
       
[:upper:]  Capital 
       
[:blank:]  Blank character （ Spaces and tabs ）
       
[:space:]  Including Spaces 、 tabs ( Horizontal and vertical )、 A newline 、 Various types of whitespace such as carriage return , Than [:blank:] It covers a wide range 
       
[:cntrl:]  Non printable control characters （ Backspace 、 Delete 、 Alarm bell ...）
       
[:digit:]  Decimal number 
       
[:xdigit:] Hexadecimal number 
       
[:graph:]  Printable non blank characters 
       
[:print:]  Printable characters 
       
[:punct:]  Punctuation 
      
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       \s     # Matches any whitespace characters , Including Spaces 、 tabs 、 Page breaks and so on . Equivalent to  [\f\r\t\v]. Be careful  Unicode Regular expressions match full space characters 
       
\S     # Matches any non-whitespace characters . Equivalent to  [^]
       
\w     # Match a letter , Numbers , Underline , Chinese characters , Characters in other countries , Equivalent to [_[:alnum:] word ]
       
\W     # Match a non letter , Numbers , Underline , Chinese characters , Characters in other countries , Equivalent to [^_[:alnum:] word ]
      
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Number of matches

Used after the character to specify the number of times , Used to specify the number of times the preceding characters will appear

       
       *       # Match preceding characters any number of times , Include 0 Time , Greedy mode ： Match as long as possible 
       
.*      # Any character of any length 
       
\?      # Match the character before it to appear 0 Time or 1 Time , namely : not essential 
       
\+      # Matches the least characters that precede it 1 Time , namely : There must be and  >=1  Time 
       
\{n\}   # Match preceding characters n Time 
       
\{m,n\} # Match preceding characters at least m Time , at most n Time 
       
\{,n\}  # Match preceding characters up to n Time ,<=n
       
\{n,\}  # Match preceding characters at least n Time 
      
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example ：

       
       [[email protected] ~]#cat goole
       
goole
       
gole
       
goooole
       
gle
       
go0989779ljiole
       
g43590kjiwele
       
[[email protected] ~]#cat goole | grep 'go*le'
       
goole
       
gole
       
goooole
       
gle
       
[[email protected] ~]#cat goole | grep 'go.*le'
       
goole
       
gole
       
goooole
       
go0989779ljiole
       
[[email protected] ~]#cat goole | grep 'go\?le'
       
gole
       
gle
       
[[email protected] ~]#cat goole | grep 'go\+le'
       
goole
       
gole
       
goooole
       
[[email protected] ~]#cat goole | grep 'go\{2\}le'
       
goole
       
[[email protected] ~]#cat goole | grep 'go\{2,4\}le'
       
goole
       
goooole
       
[[email protected] ~]#cat goole | grep 'go\{,4\}le'
       
goole
       
gole
       
goooole
       
gle
       
[[email protected] ~]#cat goole | grep 'go\{2,\}le'
       
goole
       
goooole
       
---------------------------------------------------------------------------
       
[[email protected] ~]#cat goole 
       
-1
       
-2
       
123
       
-123
       
-234
       
32432
       
[[email protected] ~]#cat goole |grep '\-\?[0-9]\+'
       
-1
       
-2
       
123
       
-123
       
-234
       
32432
       
[[email protected] ~]#cat goole |grep '\-[0-9]\+'
       
-1
       
-2
       
-123
       
-234
       
--------------------------------------------------------------------------
      
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Position anchoring

Position anchoring can be used to locate the position that appears

       
       ^           # Anchor anchoring ,  Left most for mode 
       
$           # Tail anchoring , For the far right side of the pattern 
       
^PATTERN$   # For pattern matching entire line 
       
^$          # Blank line 
       
^[[:space:]]*$     # Blank line 
       
\<  or  \b           # Initial anchoring , For the left side of the word pattern   # Try not to use \b, stay grep When searching \b and \< Different effects 
       
\>  or  \b           # Suffix anchor , For the right side of the word pattern   # Try not to use \b, stay grep When searching \b and \< Different effects 
       
\<PATTERN\>        # Match the whole word 
       
# Be careful :  Words are made up of letters , Numbers , Underline composition 
      
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example ：

       
       [[email protected] ~]#grep ^[^#] /etc/fstab
       
UUID=69617dca-2b4d-4664-ac18-051ffddf7f30 /                       xfs     defaults        0 0
       
UUID=7c7f9ef6-8873-49ff-8abf-4dd4817ea481 /boot                   xfs     defaults        0 0
       
UUID=9c5979a7-43fa-436c-8360-c2545dd81120 none                    swap    defaults        0 0
       
[[email protected] ~]#grep '^$\|^#' /etc/fstab
       
#
       
# /etc/fstab
       
# Created by anaconda on Sat Jul  2 02:32:29 2022
       
#
       
# Accessible filesystems, by reference, are maintained under '/dev/disk/'.
       
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info.
       
#
       
# After editing this file, run 'systemctl daemon-reload' to update systemd
       
# units generated from this file.
       
#
       
[[email protected] ~]#grep -v '^$\|^#' /etc/fstab
       
UUID=69617dca-2b4d-4664-ac18-051ffddf7f30 /                       xfs     defaults        0 0
       
UUID=7c7f9ef6-8873-49ff-8abf-4dd4817ea481 /boot                   xfs     defaults        0 0
       
UUID=9c5979a7-43fa-436c-8360-c2545dd81120 none                    swap    defaults        0 0
      
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grouping

grouping ： Use () Binding multiple characters together , Treat it as a whole , Such as ：(root) or (root)+ Backward reference ： The matching contents of the patterns in grouping brackets will be recorded in the internal variables by the regular expression engine , These variables are named : \1, \2, \3, ... , \1 Represents the character to which the pattern between the first open bracket from the left and the matching right bracket matches . Be careful ： Backward reference The character that matches the pattern in the grouping bracket before the reference , Not the pattern itself Be careful : \0 Represents all characters that the regular expression matches

example ：

       
       user(root):(100)/bin/(noloing).*  
       
\1 :  Indicates the contents in the first parenthesis from left to right ：root
       
\2 ： Indicates the contents in the second parenthesis from left to right ：100
       
 And so on 
      
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perhaps

perhaps ：|

       
       a\|b        #a or b
       
C\|cat      #C or cat
       
\(C\|c\)at  #Cat or cat
      
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example ： Empty lines and exclusion # Beginning line

       
       [[email protected] ~]#grep -v '^#' /etc/init.d/functions |grep -v '^$'    notes ：^# Said to # start ,-v Representation inversion ,^$ Indicates a line that begins with a hyphen , That is, the empty line 
       
[[email protected] ~]#grep -v '^#|^$' /etc/init.d/functions
       
[[email protected] ~]#egrep -v '^(#|$)' /etc/init.d/functions 
       
[[email protected] ~]#grep  '^[^#]' /etc/init.d/functions      ##  No # The first character ,grep  The default is line display , If added  -o  Options , You cannot eliminate empty lines and # Beginning line 
      
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Extended regular expression metacharacter

Character matching

       
       .            Any single character 
       
[wang]       Characters for the specified range 
       
[^wang]      Characters not in the specified range 
       
[:alnum:]    Letters and numbers 
       
[:alpha:]    Represents any English case character , or  A-Z, a-z
       
[:lower:]    Lowercase letters , Example :[[:lower:]], amount to [a-z]
       
[:upper:]    Capital 
       
[:blank:]    Blank character （ Spaces and tabs ）
       
[:space:]    Horizontal and vertical white space characters （ Than [:blank:] It covers a wide range ）
       
[:cntrl:]    Non printable control characters （ Backspace 、 Delete 、 Alarm bell ...）
       
[:digit:]    Decimal number 
       
[:xdigit:]   Hexadecimal number 
       
[:graph:]    Printable non blank characters 
       
[:print:]    Printable characters 
       
[:punct:]    Punctuation 
      
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Number matching

       
       *        Match preceding characters any number of times 
       
?       0 or 1 Time 
       
+       1 Times or times 
       
{n}      matching n Time 
       
{m,n}    At least m, at most n Time 
      
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Position anchoring

       
       ^        Head of line 
       
$        At the end of the line 
       
\<, \b   Initials 
       
\>, \b   At the end of the sentence 
      
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Group other

       
       ()       grouping 
       
 Backward reference ：\1, \2, ...  Be careful : \0  Represents all characters that the regular expression matches 
       
|        perhaps 
       
a|b     a or b
       
C|cat   C or cat
       
(C|c)at Cat or cat
      
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example ：

       
       [[email protected] ~]#ifconfig |egrep -o "(([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])"          ## [1-9]?[0-9]  Express 1 Number of digits or 2 digit   ;|  Represents or ; 1[0-9]{2}  Express 100-199 Of  ;2[0-4][0-9]  Express 200-249 ;25[0-5]  Express 250-255
      
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