online_admins << "[src.key] [src.realname] has logged out."

online_admins -= src

Problem description:

i didnt put the full thing this whole thing has 3 errors
Good question, let us know.

Does it ever get called?
Did you add the admins to the list?
did you ever call the parent?

Please try to gather some basic info or/and post all related codes.
I'll assume online_admins is a list, which would also lead me to assume that /mob's or /client's are in said list.

Just for() loop through the list, and individually output the text string.

Next time, supply more data besides "i has code, fix plox"
In response to Maximus_Alex2003
Not true, you can output to a list with no issue (just like you output to the list world).