string - Bash- getting rid of duplicate chars from a set in output -

string - Bash- getting rid of duplicate chars from a set in output -

scenario 1: have variable string contained:

output="abdh748mdn78##j*&#"

the special characters belong set called specialchars

specialchars='@#$%&*+-='

all want christmas

1) maintain 1 of specialchar, discard rest.

2) delete multiple occurrence of 1 char string, or alternatively- take 1 of special chars , discard rest.

scenario 2:

output="a#bdh#748m#" speicalchar="$char" [where $char '#' randomly selected set- above]

notice there multiple #'s

just need rid of duplicate , maintain one. echo $output

i tried:

echo $stringout | sed 's/\([@#$%&*+-=]\)\1/\1/g'

found on stackx doesn't work.

need maintain bash (can utilize bash utils).

string bash shell sed duplicate-removal