OP_EQUALVERIFY - Equality with Termination

2. OP_EQUALVERIFY — Equality with Termination

Overview

OP_EQUALVERIFY is the asserting variant of OP_EQUAL. While OP_EQUAL compares two items and leaves a boolean on the stack for further processing, OP_EQUALVERIFY performs the same comparison but immediately terminates script execution with failure if the items are not equal. If they are equal, it leaves nothing on the stack and execution continues normally.

Opcode value: 0x88 Hex: 88

It is semantically equivalent to:

OP_EQUAL OP_VERIFY

But it is a single, more efficient opcode that achieves the same result.

Behavior Breakdown

Stack before: [ <item_A> <item_B> ]
                               ↑ top

OP_EQUALVERIFY:
  - Pops item_B (top)
  - Pops item_A
  - Compares byte-by-byte
  - If EQUAL: does nothing (stack unchanged minus the two popped items), continues execution
  - If NOT EQUAL: terminates script immediately → transaction INVALID

Stack after (if equal): [ ] (two items removed, nothing pushed)
Stack after (if not equal): Script terminates with failure

The Critical Difference from OP_EQUAL

The key distinction:

| Opcode | If Equal | If Not Equal | |