Generating RegEx pattern for a given string

Question

I need to generate a RegEx pattern for a file name validation. But I am not used to RegEx pattern. I did try to generate patterns by using think link. I generated a pattern (^.*$)|(^.*i.*$) but it is not working as desired and got new pattern ^\d+(?:_[A-Za-z]+)?$ from an answer but some new conditions are required which I have listed below.

My required validations are as follows :

1234567890 => Valid
1234567890_Alphabet => Valid, '_' symbol is valid, other symbol as well as white space characters are invalid.
1234567890 - Alphabet => Invalid
1234567890alphabet => Invalid

New conditions :

11244422_134444_john => Valid
1234322_1234431 john => Invalid
1234222_134322-john => Invalid
12422344_12453222 => Valid

Some other validations :

The string should start as numeric but not alphabet. i.e. Numeric only
Underscore(_) preceded by numbers.

The fourth bird · Accepted Answer · 2021-07-27 15:12:27Z

2

Start by matching the digits, and optionally match an underscore and ASCII chars A-Za-z.

^\d+(?:_\d+)?(?:_[A-Za-z]+)?$

^ Start of string
\d+ Match 1+ digits
(?:_\d+)? Optionally match _ and 1+ digits
(?:_[A-Za-z]+)? Optionally match _ and 1+ times any of A-Za-z
$ End of string

Regex demo

edited Jul 27, 2021 at 15:12

answered Jul 20, 2021 at 15:50

The fourth bird

165k16 gold badges61 silver badges75 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

SudeepShakya Over a year ago

thank you for the answer but I have some new conditions that I have added in the description. Can u suggest some changes for new condition ? I tried to modify your regex pattern but couldn't succeed.

The fourth bird Over a year ago

@SudeepShakya Did you change the question?

SudeepShakya Over a year ago

I added few new conditions. New conditions : 11244422_134444_john => Valid, 1234322_1234431 john => Invalid, 1234222_134322-john => Invalid, 12422344_12453222 => Valid

The fourth bird Over a year ago

@SudeepShakya Like this? ^\d+(?:_\d+)?(?:_[A-Za-z]+)?$ regex101.com/r/lJNYSc/1

SudeepShakya Over a year ago

I will try and verify it .

|

malarres · Accepted Answer · 2021-07-20 15:50:38Z

2

[0-9]+($|_[A-Za-z]+)

see https://regex101.com/r/X5BMJ1/1 for live example

Basically, you get numbers first, and that's it ($) or you require _ followed by letters

answered Jul 20, 2021 at 15:50

malarres

2,9481 gold badge24 silver badges37 bronze badges

Collectives™ on Stack Overflow

Generating RegEx pattern for a given string

2 Answers 2

6 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related