10个常用的正则表达式

Regular expression is an art of the programing, it’s hard to debug , learn and understand, but the powerful features are still attract many developers to code regular expression. Let’s explore the following 10 practical regular expression ~ enjoy 

1. Username Regular Expression Pattern

^[a-z0-9_-]{3,15}$
^           # Start of the line
[a-z0-9_-]  # Match characters and symbols in the list, a-z, 0-9 , underscore , hyphen
{3,15}      # Length at least 3 characters and maximum length of 15
$           # End of the line

2. Password Regular Expression Pattern

((?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{6,20})

(			# Start of group
(?=.*\d)		# must contains one digit from 0-9
(?=.*[a-z])		# must contains one lowercase characters
(?=.*[A-Z])		# must contains one uppercase characters
(?=.*[@#$%])		# must contains one special symbols in the list "@#$%"
.			# match anything with previous condition checking
{6,20}		# length at least 6 characters and maximum of 20
)			# End of group

3. Hexadecimal Color Code Regular Expression Pattern

^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$

^		#start of the line
#			# must constains a "#" symbols
(			# start of group #1
[A-Fa-f0-9]{6} 	# any strings in the list, with length of 6
|			# ..or
[A-Fa-f0-9]{3} 	# any strings in the list, with length of 3
)			# end of group #1
$			#end of the line

4. Email Regular Expression Pattern

^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9]+
(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$

^			#start of the line
[_A-Za-z0-9-]+		# must start with string in the bracket [ ], must contains one or more (+)
(			# start of group #1
\\.[_A-Za-z0-9-]+  # follow by a dot "." and string in the bracket [ ], must contains one o                     #r more (+)
)*			# end of group #1, this group is optional (*)
@			# must contains a "@" symbol
[A-Za-z0-9]+ 	# follow by string in the bracket [ ], must contains one or more (+)
(	 #			start of group #2 - first level TLD checking
\\.[A-Za-z0-9]+ #	 follow by a dot "." and string in the bracket [ ], must contains one or                 #more (+)
)*			#	 end of group #2, this group is optional (*)
(	 #			start of group #3 - second level TLD checking
\\.[A-Za-z]{2,} #	 follow by a dot "." and string in the bracket [ ], with minimum length o		#f 2
)			#	 end of group #3
$			#end of the line

5. Image File Extension Regular Expression Pattern

([^\s]+(\.(?i)(jpg|png|gif|bmp))$)

(		#Start of the group #1
[^\s]+		# must contains one or more anything (except white space)
(		# start of the group #2
\.		#	follow by a dot "."
(?i)		#	ignore the case sensitive checking
(		#	 start of the group #3
jpg		#	 contains characters "jpg"
|		#	 ..or
png		#	 contains characters "png"
|		#	 ..or
gif		#	 contains characters "gif"
|		#	 ..or
bmp		#	 contains characters "bmp"
)		#	 end of the group #3
)		# end of the group #2
$		# end of the string
)		#end of the group #1

6. IP Address Regular Expression Pattern

^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.
([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])$

^		#start of the line
(		#  start of group #1
[01]?\\d\\d? #    Can be one or two digits.
             #If three digits appear, it must start either 0 or 1
#    e.g ([0-9], [0-9][0-9],[0-1][0-9][0-9])
|		#    ...or
2[0-4]\\d	#    start with 2, follow by 0-4 and end with any digit (2[0-4][0-9])
| 	#    ...or
25[0-5]      #    start with 2, follow by 5 and end with 0-5 (25[0-5])
)		#  end of group #2
\. 	#  follow by a dot "."
.... 	# repeat with 3 time (3x)
$		#end of the line

7. Time Format Regular Expression PatternTime in 12-Hour Format Regular Expression Pattern

(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)

(		#start of group #1
1[012]		#  start with 10, 11, 12
|		#  or
[1-9]		#  start with 1,2,...9
)		#end of group #1
:		#    follow by a semi colon (:)
[0-5][0-9]			#   follow by 0..5 and 0..9, which means 00 to 59
(\\s)?		#        follow by a white space (optional)
(?i)		#          next checking is case insensitive
(am|pm)	#            follow by am or pm

 Time in 24-Hour Format Regular Expression Pattern

([01]?[0-9]|2[0-3]):[0-5][0-9]

(			#start of group #1
[01]?[0-9]		#  start with 0-9,1-9,00-09,10-19
|			#  or
2[0-3]			#  start with 20-23
)			#end of group #1
:			#  follow by a semi colon (:)
[0-5][0-9]		#    follow by 0..5 and 0..9, which means 00 to 59

8. Date Format (dd/mm/yyyy) Regular Expression Pattern

(0?[1-9]|[12][0-9]|3[01])/(0?[1-9]|1[012])/((19|20)\\d\\d)

(	#start of group #1
0?[1-9]		#  01-09 or 1-9
| 	#  ..or
[12][0-9]		#  10-19 or 20-29
|		#  ..or
3[01]		#  30, 31
) 	#end of group #1
/		#  follow by a "/"
(		#    start of group #2
0?[1-9]		#	01-09 or 1-9
|		#	..or
1[012]		#	10,11,12
)		#    end of group #2
/		#	follow by a "/"
(		#	  start of group #3
(19|20)\\d\\d	#	    19[0-9][0-9] or 20[0-9][0-9]
)		#	  end of group #3

9. HTML tag Regular Expression Pattern

<("[^"]*"|'[^']*'|[^'">])*>

<		#start with opening tag "<"
(		#   start of group #1
"[^"]*"	#	only two double quotes are allow - "string"
|		#	..or
'[^']*'	#	only two single quotes are allow - 'string'
|		#	..or
[^'">]		#	cant contains one single quotes, double quotes and ">"
)		#   end of group #1
*		# 0 or more
>		#end with closing tag ">"

10. HTML links Regular Expression PatternHTML A tag Regular Expression Pattern

(?i)]+)>(.+?)

(		#start of group #1
?i		#  all checking are case insensive
)		#end of group #1
#start with "
(		#  start of group #2
[^>]+		#     anything except (">"), at least one character
)		#  end of group #2
>		#     follow by ">"
(.+?)		#	match anything
#	  end with "

Extract HTML link Regular Expression Pattern

\s*(?i)href\s*=\s*(\"([^"]*\")|'[^']*'|([^'">\s]+));

\s*		#can start with whitespace
(?i)		# all checking are case insensive
href		#  follow by "href" word
\s*=\s*		   #   allows spaces on either side of the equal sign,
(		#    start of group #1
"([^"]*")   #      only two double quotes are allow - "string"
|		#	  ..or
'[^']*'	#      only two single quotes are allow - 'string'
| 	#	  ..or
([^'">]+)   #     cant contains one single / double quotes and ">"
)		#    end of group #1

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