regex substitution "." to "_"

I have a specific issue with character substitution in strings:

If I have the following strings

"..A.B....c...A..D.."
"A..S.E.Q.......AW.."
".B.C..a...R......Ds"

Which regex substitution should I use to replace the dots and obtain the following strings:

"A_B_c_A_D"
"A_S_E_Q_AW"
"B_C_a_R_Ds"

I am using R.

Thanks in advance!

>Solution :

Using stringr from the ever fantastic tidyverse.

str1 <- "..A.B….c…A..D.."

str1 %>%
  #replace all dots that follow any word character ('\\.' escapes search, '+' matches one or more, '(?<=\\w)' followed by logic)
  str_replace_all('(?<=\\w)\\.+(?=\\w)', '_') %>%
  #delete remaining dots (i.e. at the start)
  str_remove_all('\\.')

As always plenty of ways to skin the cat with regex