...he list is the expected type of the proxy server; the example above is pipe delimited - comma delimited is also common share | improve this answer | follow ...

... of invoking a command substitution (which forks the shell), starting up a pipeline, and running an external executable (tr or sed), since parameter expansion is purely a shell-internal operation. (Also, for the tr and sed solutions, the input variable should be double-quoted inside the command subs...