caller: caller [expr]
Return the context of the current subroutine call.
Without EXPR, returns "$line $filename". With EXPR, returns "$line $subroutine $filename"; this extra information can be used to provide a stack trace.
The value of EXPR indicates how many call frames to go back before the current one; the top frame is frame 0.
Exit Status:
Returns 0 unless the shell is not executing a shell function or EXPR
is invalid.