regular expression to only allow numbers, numbers with dot, & and space

Question

I'm going to need a regular expression that only allows numbers, spaces, decimal numbers with precision of 2, and & sign.

This regular expression will be used to check for an input that allows multiple numbers separated by & sign, and there can be space (optional, but maximum one) in between. The following is what I've tried, due to my poor understanding in regex, they worked so poorly.

^(?=.*[0-9])[ &.0-9]+$

but it doesn't work well.

because things like &&&&&&1 will pass the check.

have also tried things like this, which also works so poorly

^([0-9]{1,}[.]{0,1}[0-9]{0,2}[ ]{0,1}+[&]{0,1}[ ]{0,1})*?$

The following exemplifies what I expected

12 ---> (pass)

12.12 ---> (pass)

12 & 129.12 & 11 --- >(pass)

12 & 129. & 11 ---> (should not pass)

12 & .129 ---> (should not pass)

12 & 129..1 (should not pass)

12 & 129.111 (should not pass)

&&&1 (should not pass)

.......

Many thanks in advance

Answer 1

To account for the spaces, you might make them optional using ?

You might use a repeating pattern matching 2 optional spaces and an ampersand:

^\d+(?:\.\d{2})?(?: ?& ?\d+(?:\.\d{2})?)*$

Explanation

• ^ Start of string
• \d+(?:\.\d{2})? Match 1+ digits and optionally match a dot and 2 digits
• (?: Non capturing groupo
  • [ ]?&[ ]? Match an optional space (used [ ] for clarity), & and optional space
  • d+(?:\.\d{2})? Match 1+ digits and optionally match a dot and 2 digits
• )* Close non capturing group and repeat 0+ times to also allow a single entry
• $ End of string

Regex demo