How to write a regular expression with a condition?

Question

Regular Expressions

The following strings are possible:
#name
#name#
name# You
need to find characters #only if:
- either it comes at the end
- or it goes both at the beginning and at the end at the same time.
In other words: if there is a character #at the end, then you need to select all the characters #in the string.
Tried through a condition, but it doesn't work: if it's at the end #- then select everything for me #
(#)$(?(1)#)
. How can I compose such a regular expression?

Answer 1

Like this https://regex101.com/r/m08j7m/5 ?

Answer 2

Alexander needs to highlight only the characters #without what stands between them.