Tab-completion currently exists in mpsh in a very primitive form.
mpsh uses gnu readline, but doesn't talk to it, so behaviour is
for default filename completion, with no substitutions. ie:
$HOME/blah<tab> won't work, because $HOME isn't evaluated
until the entire line is entered.
Also, command tab-completion doesn't work as one would hope. However, filename globbing for command names is treated specially, inspired by the non-interactive command expansion of Multics, NOS, & VMS. So this:
mpsh$ do-some*ng args
Will expand to the first match in the directories listed in $PATH.