Regular expression for optional character in between the numerals

Question

I need to validate a string that contains underscore(_) in between the numbers. Underscore character is an optional. Only condition is, it should be between the numbers.

Valid     => 123
Valid     => 1_23
Valid     => 123_4567_89_312_575

Not valid => 123_
Not valid => _123
Not valid => 123__12   (Two consecutive underscore characters)
Not valid => _         (Number is mandatory)
Not valid => abc       (only numbers and _ should be present)

I have tried this regular expression

([0-9]+_*[0-9]+)*

It failed. Any idea why ?

PS: Going to implement this in swift language. Core logic: Underscore character is used like a separator for numbers.

Wiktor Stribiżew · Accepted Answer · 2018-05-12T19:14:52.050

Your ([0-9]+_*[0-9]+)* pattern matches 0+ repetitions of 1+ digits, 0+ underscores and then 1+ digits. So, it can match 12, 3_______4, 2345, and an empty string. Depending on what method you are using it in, it may match partial, or the whole string.

You may use

^[0-9]+(?:_[0-9]+)*$

See the regex demo

If you use the pattern inside NSPredicate with MATCHES, the ^ and $ anchors are not necessary as in that case the whole string should match the pattern.

Details

^ - start of string
[0-9]+ - 1+ digits
(?: - start of a non-capturing grouping
- _ - an underscore
- [0-9]+ - 1+ digits
)* - repeats the pattern sequence 0 or more times
$ - end of string.

score 3 · Answer 2 · edited Jun 20 '20 at 09:12

3

Simple it should be either:

^[0-9]+(_[0-9]+)*$ or

^\d+(_\d+)*$ ,

both of which means start with any number(<number>) then have any(zero or more) number of combinations of pattern(_<number>) underscore and number.

OR vice-versa,

([0-9]+_)*[0-9]+ or

(\d+_)*\d+ ,

both of which means start with any(zero or more) number of combinations of pattern(<number>_) number and underscore; and then have any number(<number>).

edited Jun 20 '20 at 09:12

Community

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answered May 12 '18 at 19:09

beingmanish

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@curiousManish: Now you copied my answer – Jogendar Choudhary May 12 '18 at 20:10
@AbdelahadDarwish: now its cover all cases – Jogendar Choudhary May 12 '18 at 20:11
Sorry @JogendarChoudhary I don't think so, both of them have same meaning,just added another approach to achieve this. And btw i didn't copied you answer ("^[0-9]+(_*[0-9]+)*$") which you later realized was incorrect and u updated your answer to match with mine. Anyway happy days, enjoy dude ! – beingmanish May 12 '18 at 20:22

Jogendar Choudhary · Answer 3 · 2018-05-12T19:39:47.180

2

You may use this expression:

^\d+(_\d+)*$

edited May 12 '18 at 19:39

answered May 12 '18 at 19:22

Jogendar Choudhary

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oh u very smartly edited and matched with mine regex, finally ! – beingmanish May 12 '18 at 19:38
Please check, this is not yours – Jogendar Choudhary May 12 '18 at 19:40
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oh man you just deleted your 1st answer and posted one which is another form of mine regex, which also says start with number and then have any combination of (_)*. Anyway, whatever it is not sure what you want to achieve by again and again deleting and changing your answers, it's good that finally you realized that your initial answer("^[0-9]+(_*[0-9]+)*$";) was incorrect. – beingmanish May 12 '18 at 19:45
Yes man, That time I didn't read question bottom line "PS: Two consecutive underscore character is invalid. Going to implement this in swift language." that's why. Thank you – Jogendar Choudhary May 12 '18 at 19:46

Regular expression for optional character in between the numerals

3 Answers3