Debuggers
Debuggers
Ruby comes with a debugger, accessible on the command line, for stepping through problems with programs (see Figure 9.1). Type the following to access it:
Figure 9.1. Accessing the Ruby command-line debugger
Ruby r debug MyProgramScript.rb
The debugger has a number of useful commands for, well, debugging a Ruby program. These are listed in Table 9.1.
|
Command |
Use |
|---|---|
|
break |
Set breakpoint at specified line or method |
|
watch |
Set a watchpoint for an expression |
|
catch |
Set a catchpoint for an exception |
|
delete |
Delete breakpoints or watchpoints |
|
display |
Set display expression to be printed when program stops |
|
undisplay |
Unset display |
|
cont |
Continue program execution |
|
step |
Step forward in the program until the next source line |
|
next |
Step forward in the program until the next source line. Treat method calls as one instruction |
|
list |
List line of source code |
|
up |
Select stack frame that called current stack frame |
|
down |
Select stack frame called by current stack frame |
|
finish |
Execute until selected stack frame returns |
|
trace |
Turn trace mode on or off |
|
quit |
Exit debugger |
|
var global |
Show global variables in current stack frame |
|
var local |
Show local variables in current stack frame |
|
var instance |
Show instance variables of the given object |
|
var const |
Show constants of the given object |
|
method instance |
Show methods of the given object |
|
method |
Show instance methods of the given class or module |
|
thread list |
Show thread list |
|
thread current |
Show current thread |
|
thread |
Switch to a given thread |
|
thread stop |
Stop the given thread |
|
thread resume |
Resume the given thread |
|
p |
Evaluate the given expression in current stack frame and show its value |
|
help |
Print debug commands |
|
else |
Evaluate input in the current stack frame and show its value |
  |