RegeX for a range and limit together

Question

I am new to regeX and I am looking for a expression which satisfy the below condition

should validate numbers only. decimal is not accepted.(eg :123, 11, 1025,0548)
should not greater than 7 digits

I tried the below regeX

^[1-9][0-9]*$

but it works fine for numbers which greater than 0.

and then I tried

 ^[1-9][0-9]\d{1,7}$

but it accept if the digits is greater than 2 numbers. when I give 12 it returns false. when I give 123 it returns true

and when I give 0124 this will also return false

please refer the below points also for different inputs

1, 12, 432, 12414, 1234567 etc all are valid inputs. its greater than 0 and max length is 7
01, 0121, 0000001 etc are also valid. 0000001 is greater than 0.
0, 12345678 etc are invalid, because it should not accept less than 0 or length greater than 7
all negative values are invalid, all characters are invalid

@TimBiegeleisen not working. I dont want to accept if the value is `0`. when I give `0` it returns false. — Sandeep Sudhakaran, Nov 06 '19 at 13:38
@WiktorStribiżew not working. I gave input `0121`. it should accept. please read my questions — Sandeep Sudhakaran, Nov 06 '19 at 13:40
@WiktorStribiżew Very bad dupe target. This is well put together question an not answerable by the target. — ruohola, Nov 06 '19 at 13:45
@WiktorStribiżew I saw that answer too, but it doesn't satisfied me. sorry. — Sandeep Sudhakaran, Nov 06 '19 at 13:52
Ok, since you accepted `^(?!0+$)\d{1,7}$` all you need is a lookaround to exclude an all zero input. I changed the link. — Wiktor Stribiżew, Nov 06 '19 at 14:57

ruohola · Accepted Answer · 2019-11-06T14:08:12.737

1

You can use negative lookahead for this. This pattern will work fine:

^(?!0+$)\d{1,7}$

Explanation:

^(?!0+$) negative lookahead, which checks that the string is not all 0s. A negative lookahead means, that if this matches, the whole pattern will not match.
^ \d{1,7}$ checks that the string consists of 1 to 7 characters, which all are numbers.

(I'm reusing the ^ anchor for both the lookahead and the actual pattern, because they can share it, since the lookahead is at the start. The ^ could also be added to the lookahead: (?!^0+$), but it wouldn't affect anything.)

regex101 demo

edited Nov 06 '19 at 14:08

answered Nov 06 '19 at 13:37

ruohola

21,987
6
62
97

it is working fine. can you please explain what it does? it would be helpful – Sandeep Sudhakaran Nov 06 '19 at 13:53
@SandeepSudhakaran Added an explanation :) – ruohola Nov 06 '19 at 13:59
Thanks for the explanation, I can apply this to other area also. – Sandeep Sudhakaran Nov 06 '19 at 14:05

The fourth bird · Answer 2 · 2019-11-06T13:59:08.517

1

You could us a positive lookahead (?=[0-9]*[1-9]) if supported to assert at least a digit 1-9 and then match 1- 7 digits.

^(?=[0-9]*[1-9])[0-9]{1,7}$

In parts

^ Start of string
(?= Positive lookahead, assert what is on the right is
- [0-9]*[1-9] Match 0+ times a digit 0-9, then a digit 1-9
) Close lookahead
[0-9]{1,7} Match a digit 0-9 1-7 times
$ End of string

Regex demo

edited Nov 06 '19 at 13:59

answered Nov 06 '19 at 13:39

The fourth bird

154,723
16
55
70

it is working fine. can you please explain what it does? it would be helpful – Sandeep Sudhakaran Nov 06 '19 at 13:53
@SandeepSudhakaran I have added an explanation about the separate parts. – The fourth bird Nov 06 '19 at 14:00
Thanks for the explanation and I understood. but sorry I accepted other answer because that is more convincing me. – Sandeep Sudhakaran Nov 06 '19 at 14:04
1

@SandeepSudhakaran No problem at all, good luck! – The fourth bird Nov 06 '19 at 14:11

RegeX for a range and limit together

2 Answers2