Analysis of information sources in references of the Wikipedia article "Fork bomb" in English language version.
When the shell is in POSIX mode (see Bash POSIX Mode), fname must be a valid shell name and may not be the same as one of the special builtins (see Special Builtins). In default mode, a function name can be any unquoted shell word that does not contain '$'.
bash$ :(){ :|:&};:}
Name: In the shell command language, a word consisting solely of underscores, digits, and alphabetics from the portable character set. The first character of a name is not a digit.