OP_NOT

INFO

Opcode number: 145
Byte representation: 0x91
Short description: Pop the top item and push 1 if it is zero; otherwise, push 0.

OP_NOT pops the top item on the stack and checks if it is zero. If it is, OP_NOT pushes 1 (true) onto the stack. If the item is non-zero, it pushes an empty array (false). This operation is often used in conditional scripts to invert the truthiness of a value.

Operation

1. Pop the top item on the stack.
2. Check if it is zero.
3. If the item is zero, push 1 (true) onto the stack.
4. If the item is non-zero, push an empty array (false) onto the stack.

Notes

• In Bitcoin Script, an empty array represents false, while 1 represents true.
• If the stack is empty when OP_NOT is executed, the script will fail.

Examples

Example 1

Using OP_NOT with a zero item:

# ASM script
OP_0 OP_NOT

# Raw script
0091

# Stack (before OP_NOT)
(empty array)

# Stack (after OP_NOT)
1

Example 2

Using OP_NOT with a non-zero item:

# ASM script
OP_1 OP_NOT

# Raw script
5191

# Stack (before OP_NOT)
1

# Stack (after OP_NOT)
(empty array)