Adjust regex to also match partial expression

Question

Is there a generic way to wrap an existing regex to also accept partial matches?

For example verifying an IPV4 address one can use ((?:(?:25[0-5]|2[0-4]\d|1?\d{1,2})(?:\.(?!$)|$)){4})

Now this works for

• 10.0.10.1

But not for

• 1
• 10
• 10.0
• 10.0.
• 10.0.1
• 10.0.10
• 10.0.10.

I want to provide a generic way to wrap the existing regex (or any else) without modifying it into a new regex that accepts any amount of partial ip addresses.

UPDATE: The intention of this is to use it as a mask for a text field thus I need to allow partial strings otherwise it would only work by inserting the complete IP at once e.g. via pasting from clipboard.

Answer 1

I suggest:

^(?:\b\.?(?:1\d{0,2}|[3-9]\d?|2(?:[0-4]\d?|5[0-5]?|[6-9])?|0|$)){0,4}$

demo

Feel free to change the last quantifier to {1,4} if you do not want the empty string to be valid.

Notices:

• consecutive dots are avoided using a word-boundary at the start of the main group.
• this word-boundary also avoids a dot at the start the field.
• about the group that contains numbers description:
  • branches are ordered by probability of the starting digit (111 numbers start with 1, 77 start with [3-9], etc.)
  • the last branch is the end of the string anchor $ to allow a trailing dot. It is more efficient to do that and less problematic than making the whole group optional