s_subst
if ((cmd->u.s = calloc(1, sizeof(struct s_subst))) == NULL)
compile_subst(char *p, struct s_subst *s)
compile_flags(char *p, struct s_subst *s)
static char *compile_flags(char *, struct s_subst *);
static char *compile_subst(char *, struct s_subst *);
struct s_subst *s; /* Substitute command */