boolarg - parse boolean argument or ask user

int boolarg (ptr,brk,prompt,defalt);
char **ptr,*brk,*prompt;
int defalt;

Boolarg attempts to parse an argument from a string, passing the
string pointer ptr and the break character set brk to the nxtarg(3)
routine. If there is an argument parsed, and it is a legal
boolean, then its value is returned by boolarg. If there is no
argument, or it is not valid, then an error message is printed to
stderr and the routine getbool(3) is passed the remaining
arguments. The value of getbool is then returned by boolarg.

Boolarg is especially useful for parsing boolean values from
argument lists in programs using the command interpreter, ci(3).

nxtarg(3), getbool(3), ci(3)