Begin/rescue/end blocks in Ruby - Step-by-Step Execution

Concept Flow - Begin/rescue/end blocks

Start begin block

↓

Execute code inside begin

↓

Error?

No→End begin block

Yes↓

Enter rescue block

↓

Handle error

↓

End begin block

The program tries code inside begin. If an error happens, it jumps to rescue to handle it, then ends the block.

Execution Sample

Ruby

begin
  puts 10 / x
rescue ZeroDivisionError
  puts "Cannot divide by zero"
end

Tries to divide 10 by x; if x is zero, rescue prints a message instead of crashing.

Execution Table

Step	Action	Code Line	Result	Output
1	Start begin block	begin	Begin block started
2	Execute division	puts 10 / x	Error: undefined local variable or method `x'
3	Error caught	rescue ZeroDivisionError	No ZeroDivisionError, but NameError raised
4	Unhandled error	end	Program crashes with NameError

💡 Execution stops due to unhandled NameError because x is not defined

Variable Tracker

Variable	Start	After Step 2	Final
x	undefined	undefined	undefined

Key Moments - 2 Insights

Why does the rescue block not catch the error in step 2?

Because the error is NameError (undefined variable), but rescue only catches ZeroDivisionError as shown in execution_table row 3.

What happens if the error matches the rescue type?

The program jumps to the rescue block to run its code, then continues after end, preventing a crash.

Visual Quiz - 3 Questions

Look at the execution table, what error occurs at step 2?

A No error

B ZeroDivisionError

C NameError

D SyntaxError

💡 Hint

Check the 'Result' column in step 2 of the execution_table

At which step does the program crash due to unhandled error?

A Step 4

B Step 1

C Step 3

D Step 2

💡 Hint

Look at the 'Result' column for step 4 in execution_table

If x was zero, which step would rescue handle the error?

A Step 2

B Step 3

C Step 4

D Step 1

💡 Hint

Rescue handles ZeroDivisionError as shown in step 3 of execution_table

Concept Snapshot

begin
  # code that might fail
rescue ErrorType
  # code to handle error
end

- begin runs code
- rescue catches errors of given type
- end closes block
- prevents program crash by handling errors

Full Transcript

This example shows how Ruby's begin/rescue/end blocks work. The program tries to run code inside begin. If an error happens, it looks for a matching rescue block to handle it. If the error matches, rescue runs its code to fix or report the problem, then the program continues safely. If no rescue matches, the program crashes. In the example, dividing by x causes an error. Since x is not defined, a NameError happens, but rescue only catches ZeroDivisionError, so the program crashes. If x was zero, rescue would catch the division error and print a message instead of crashing.