You can find the Regular Expression (Regex) fundamentals with given examples that you can use in your daily works.

1. REGEX
Regular Expression
Mesut Güneş
www.testrisk.com

2. Regular expressions are
patterns
used to match
character combinations
in strings[1].
What it is?

3. 1956: Stephen Cole Kleene, Regular
Language
1968: Ken Thompson, Pattern Matching,
Text editor
1970: Bell Labs, in Unix
1980: Henry Spencer, PERL
1992: POSIX.2 (UNIX Shell), Many
languages [2]
History

4. Hi,
I called Jon on Tuesday, March 25th at 7pm
and expressed a concern about my slow times
accessing www.cnn.com. He said he would fix
it, but I never heard back. Can someone contact
me at Kellie.Booth@if.com ASAP? What does
Ctrl-F5 mean, by the way?
Thanks
Kellie
Human Brain VS Text Processing

5. Hi, …., thanks
I called …
March 27th
ww.blabla.com
Patterns?

6. (Hi|Hello),w{1,}(Regards|Thanks)
Is(verb|auxiliary)(*)
Marchsd(st|nd|rd|th)
www.w{1,}.(com|net|edu|…)
Patterns?

7. /pattern/options
Regex syntax

8. ^ $ . | { } [ ] ( ) * + ?
Literal Characters
(metacharacters)

9. provide a list of potential
matching characters at a
position in the search
text
Square Brackets
7[Pp][Mm]

10. more examples
Square Brackets
7[Pp][Mm]
[123456789][aApP][Mm]
[1-9][aApP][Mm]

11. provide characters cannot enter
to regex
Non-Printable Characters
n - Matches a new line; Windows rn
t - Matches a tab character.
b - Matches a backspace (when used between brackets)
a - Matches the bell character.
r - Matches a carriage return.
f - Matches Form feed.
v - Matches a vertical tab.
Euro € - u20AC
British pound £ - u00A3
Yen ¥ -u00A5
Dollar sign $ - $ or u0024 or x24
cX - Matches an ASCII control character, such as cC is Ctrl-C.

12. provide list of
excludation
Negation
[^0-9A-F]
[^a-zA-Z0-9_] negative of w (or
W)

13. repetition of
characters
Curly Brakets
{n} : “n” times.
{n,} : At least “n” times, but no upper
limit.
{n,m} : Between “n” and “m” times.

14. repetition
characters
Quantifier Symbols
Quantifier Matches Same as
? Match zero or one time {0,1}
* Match zero or more times {0, }
+ Match one or more times {1, }

15. define the string
boundaries
Starting and Ending Pattern
^ : starting string, not inside []
$ : end of string

16. provides
alternatives
Alternation
(x|y|z)
(www|ftp)
www.w{1,}.(net|com|org|edu)

17. (x|y|z) vs [xyx]
Alternation
(x|y|z) : can be used for string
[xyz][a-A0-9] : one character or
list of characters
(Regex|ReGex) - Re[gG]ex

18. .
Any single character

19. [abc]
A single character: a, b, or c

20. [^abc]
Any single character but a, b, or c

21. [a-z]
Any single character in the range
a-z

22. [a-zA-Z]
Any single character in the range a-z or
A-Z

23. ^
Start of line

24. $
End of line

25. A
Start of string

26. z
End of string

27. s
Any whitespace character

28. S
Any non-whitespace character

29. d
Any digit

30. D
Any non-digit

31. w
Any word character (letter, number,
underscore)

32. W
Any non-word character

33. b
Any word boundary character

34. (...)
Capture everything enclosed

35. (a|b)
a or b

36. i
Case insensitive option.

37. x
ignore whitespace in regex

38. (? (name)
<pattern>)
Grouping

39. (?: <pattern>)
Non-Capturing Group

40. check if the pattern follows by
another
Look Ahead
(?=<pattern>) : positive look ahead
(?!<pattern>) : negative look ahead
(?<city>w+)[, ]+(?= NJ|PA|DE)

41. check if the pattern precede by
another
Look Behind
(?<=<pattern>) : positive look ahead
(?<!<pattern>) : negative look ahead
(?<="state":)[
].*(?<state>PA|Pennsylvania)

42. EXAMPLES

43. ^(?!.*(?:<|>|&|’|"|%|;|-|+|(|)|s)).{6,20}$
password
should be 6 to 20 characters length
and
not include the followings:
< > & ’ ” % ; - + ( )

44. Let’s Dig-into Pattern
English Rule Regex Pattern
BEGINNING of the string ^
Start of NEGATIVE LOOKAHEAD (?!
Multiple any word except newline, with QUANTIFIER .*
Start of NON-CAPTURING group (?:
Single CHARACTER with ALTERNATION <|
More single CHARACTER with ALTERNATION
>| &| ‘| “| %| ;| -| +| (|
)| s
Repetition with boundaries {6,20}
END string $
^(?!.*(?:<|>|&|'|"|%|;|-|+|(|)|s)).{6,20}$

45. ack '(?<="GET")[,]"/nike.*'
unix shell
Find all “GET” requests to “nike” in all .csv files:
~/Downloads ls *.csv | wc -l
109
~/Downloads ack '(?<="GET")[,]"/nike.*' | wc -l
88
~/Downloads cat web_3000:25.csv | grep '/nike.*'
"GET","/arama/nike",7,0,140,665,101,3797,196168,0.09
"GET","/kampanya/arama/nike",8,0,270,678,229,2641,164205,0.11
"GET","/nike/295/morhipo-ozel",2,0,81,88,81,95,121609,0.03
"GET","/nike/markalar/503/32026/marka?fh=discount_rate_catalog01]

46. BDD - Cucumber

47. ^/(Questions|Sorular|‫$/*)پرسش‬
Thanks
Reference:
[1] https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions
[2] https://en.wikipedia.org/wiki/Regular_expression
[3] Regular Expression Succinctly, Syncfusion, by Joe Both
[4] http://www.slideshare.net/adamlowe/regex-cards-powerpoint-format
[5] https://regex101.com
Mesut Güneş
www.testrisk.com