By mkyong – November 18, 2009
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
==> See the explanation and example here
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 “@#$%”
. # match anything with previous condition checking
{6,20} # length at least 6 characters and maximum of 20
) # End of group
==> See the explanation and example here
3. Hexadecimal Color Code Regular Expression Pattern
^#([A–Fa–f0–9]{6}|[A–Fa–f0–9]{3})$
^ #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
==> See the explanation and example here
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 or 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 of 2
) # end of group #3
$ #end of the line
==> See the explanation and example here
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
==> See the explanation and example here
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
==> See the explanation and example here
7. Time Format Regular Expression Pattern
Time 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
==> See the explanation and example here
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
==> See the explanation and example here
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
==> See the explanation and example here
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 “>”
==> See the explanation and example here
10. HTML links Regular Expression Pattern
HTML A tag Regular Expression Pattern
(?i)<a([^>]+)>(.+?)</a>
( #start of group #1
?i # all checking are case insensive
) #end of group #1
<a #start with “<a”
( # start of group #2
[^>]+ # anything except (“>”), at least one character
) # end of group #2
> # follow by “>”
(.+?) # match anything
</a> # end with “</a>
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
chuckezell.com 