When the xtrace option is enabled with the $PS4 variable containing a command substitution, the expansion of the variable is likely to fall into an infinite loop because of recursive trace for commands in the command substitution. Other existing shells prevent this issue by suppressing recursive trace.
magicant 
When the xtrace option is enabled with the $PS4 variable containing a command substitution, the expansion of the variable is likely to fall into an infinite loop because of recursive trace for commands in the command substitution. Other existing shells prevent this issue by suppressing recursive trace.