I need to match a group of exact 5 characters 1's. Example below

02011111020 // match
00211111200 // Not match because there are 2 at start and end of group
00111111100 // Not match because there are 6 1's

So far, I have try with pattern

• (?!2)(1{5}?)(?!2) but fail at 00111111100
• \D(1{5}?)\D but fail at 02011111020

CodePudding user response：

This condition (?!2) is always true as the next character to match is a 1 and this condition (?!2) asserts not a 2, which will be true if there is still a 1 to the right.

This \D means matching a character other than a digit, which can never match in a string with only digits.

You can exclude matching 1 and 2 using a character class [12] and lookarounds:

(?<![12])1{5}(?![12])

The pattern matches:

• (?<![12]) Negative lookbehind, assert not 1 or 2 to the left
• 1{5} match 5 times a 1
• (?![12]) Negative lookahead, assert not 1 or 2 to the right

Regex demo

CodePudding user response：

Matching a line with 5 consecutive 1s that are preceded and followed by a 0:

.*01{5}0.*