OP_NOTIF ​

OP_NOTIF is used to perform conditional execution, similar to OP_IF but operates inversely. Scripts will execute the next segment if a zero element is popped from the stack.

Operation ​

1. Pop the top stack item.
2. If the item is 0, execute the following opcodes until an OP_ELSE or OP_ENDIF is encountered.
3. If the item is non-0, skip the following opcodes until an OP_ELSE or OP_ENDIF is encountered.

You'll see it used like so:

<condition> OP_NOTIF
    <script if condition is false>
OP_ELSE
    <script if condition is true>
OP_ENDIF

Where <condition> is some operation or value that will leave a 0 or non-0 value on top of the stack.

Notes ​

• As with OP_IF, if there's no matching OP_ENDIF for an OP_NOTIF, the script will fail.

Examples ​

Example 1 ​

The following script would leave 2 on the stack as the condition (0) is false.

# ASM script
OP_0 OP_NOTIF OP_2 OP_ENDIF

# Raw script
00645268

# Final stack
2

Example 2 ​

The following script would leave 3 on the stack as the condition (1) is non-0.

# ASM script
OP_1 OP_NOTIF OP_2 OP_ELSE OP_3 OP_ENDIF

# Raw script
516452675368

# Final stack
3