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Shell script learning notes - regular expressions

2022-04-23 02:47:00 【XL's Princess】

One 、 The regular expression is in shell There are only commands in the grep、sed、awk The command supports regular expressions .

Two 、 Special characters

Locator	explain
^	Anchor the beginning ^a With a start The default anchor is one character
$	Anchor end a$ With a ending The default anchor is one character

Test cases ：

# Exactly match , With a start , With c ending ,"^ac$" It's a match ac
[root@localhost shell]# egrep "^ac$" zzbds.sh
ac
# Fuzzy matching 
[root@localhost shell]# egrep "^a" zzbds.sh
ac
ab
abbc
abcc
aabbcc
abbbc
abbbbbc
acc
abc
asb
aa
a_c
aZc
aAAAAc
a c
ababababab
[root@localhost shell]# egrep "c$" zzbds.sh
ac
abbc
abcc
aabbcc
abbbc
abbbbbc
acc
abc
a_c
aZc
aAAAAc
a c
ccc
[root@localhost shell]#

Match symbol . Match string

Match symbol	explain
.	Match any character except carriage return
（）	String grouping
[ ^ ]	Indicates the character in the character class that appears in negative brackets , Take the opposite
\	Escape character
Pipe,	or

Test cases

[root@localhost shell]# egrep "^a.c$" zzbds.sh
acc
abc
a_c
aZc
a c
[root@localhost shell]# egrep "^a[0-9]c$" zzbds.sh
a3c
[root@localhost shell]# egrep "^a[^0-9]c$" zzbds.sh
acc
abc
a_c
aZc
[root@localhost shell]# egrep "^a\*c$" zzbds.sh
a*c
[root@localhost shell]# egrep "^(a|b)c$" zzbds.sh
ac
# With a The beginning or b start 
[root@localhost shell]# egrep "^(a|b)c$" zzbds.sh
ac
bc

qualifiers ： Make a qualified description of the preceding character or string

qualifiers	explain
*	Add... After a character * Indicates that the character does not appear or appears more than once
？	Similar to the asterisk , But it means that the character appears once or does not appear
+	Indicates that the character before it appears one or more times , But there must be one
{n,m}	Appears after a character , Indicates that the character is at least n Time , most m Time
{m}	Just happened to appear m Time

Test case

[root@localhost shell]# egrep "^ab*c$" zzbds.sh
ac
abbc
abbbc
abbbbbc
abc
[root@localhost shell]# egrep "^ab?c$" zzbds.sh
ac
abc
[root@localhost shell]# egrep "^ab+c$" zzbds.sh
abbc
abbbc
abbbbbc
abc
[root@localhost shell]# egrep "^ab{2,4}c$" zzbds.sh
abbc
abbbc
[root@localhost shell]# egrep "^ab{2,5}c$" zzbds.sh
abbc
abbbc
abbbbbc
[root@localhost shell]# egrep "^ab{3}c$" zzbds.sh
abbbc

3、 ... and 、POSIX Special characters

Special characters	explain
[:alnum:]	Match any alphabetic character 0-9 a-z A-Z
[:alpha:]	Match any letter , Uppercase or lowercase
[:digit:]	Numbers 0-9
[:graph:]	Non empty character （ Non whitespace control characters ）
[:lower: ]	Lowercase characters a-z
[:upper: ]	Uppercase characters A-Z
[:cntrl:]	Control characters
[:print:]	Non empty character （ Including Spaces ）
[:punct:	Punctuation
[:blank:]	Space and TAB character
[:xdigit:]	16 Hexadecimal Numbers
[:space:]	All blank characters （ New line 、 Space 、 tabs )

Test cases

[root@localhost shell]# egrep "^a[[:alnum:]]$" zzbds.sh
ac
ab
aa
[root@localhost shell]# egrep "^a[[:alnum:]]c$" zzbds.sh
acc
abc
aZc
a3c
[root@localhost shell]# egrep "^a.c$" zzbds.sh
acc
abc
a_c
aZc
a3c
a*c
[root@localhost shell]# egrep "^a[[:upper:]]c$" zzbds.sh
aZc
[root@localhost shell]# egrep "^a[[:lower:]]*c$" zzbds.sh
ac
abbc
abcc
aabbcc
abbbc
abbbbbc
acc
abc

# Match valid ip Address ,
[root@localhost shell]# egrep '^((25[0-5]|2[0-4][[:digit:]]|[01]?[[:digit:]][[:digit:]]?).){3}(25[0-5] |2[0-4][[:digit:]]|[01]?[[:digit:]][[:digit:]]?)$' --color ip.sh
1.1.1.1
192.168.11.0
# Match with 250.-255. perhaps 200.-249. perhaps 0.-99. At the beginning , And previous rules have appeared 3 Time , And the character at the end of the previous rule 
'^((25[0-5]|2[0-4][[:digit:]]|[01]?[[:digit:]][[:digit:]]?).){3} (25[0-5] |2[0-4][[:digit:]]|[01]?[[:digit:]][[:digit:]]?)$')

>  Match phone number 
> egrep "^[[:graph:]]{12}$" numder |grep "^(0[1-9][0-9][0-9]?)-[1-9][0-9]{6,7}$"

Four 、 Expand

Insert picture description here

for example ：

1、
e:  Play chicken game , Play games tonight 
 If only filter ： Play chicken game 
 You need to ： play .*? game 
.*?  Represents as few matches as possible 
2、
 Specifies the character partition 
e：123x456x789x
 result ：
123x
456x
789x
 You need to ：.*?x

Reference resources ：
Regular expressions Don't to character string The beginning and the end （ Pre check before and after ）：https://blog.csdn.net/q965844841qq/article/details/111368696?

 matching “<a href=” And “" class="ulink"” All characters in the middle  (?<=<a href=").+(?=" class="ulink")

Online regular expression testing ：https://tool.oschina.net/regex

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