OP_PICK vs OP_ROLL - Key Difference

18. OP_PICK vs OP_ROLL — Key Difference

Overview

OP_PICK and OP_ROLL are companion opcodes that differ in exactly one fundamental behavior: OP_PICK copies the target item, while OP_ROLL moves it. Understanding this distinction is critical for writing correct Bitcoin scripts.

Side-by-Side Comparison

Starting Stack: [ A, B, C, D ]   (D is top)
Push n = 2:     [ A, B, C, D, 2 ]

OP_PICK result: [ A, B, C, D, B ]
  - B (position 2) is COPIED to top
  - Original B remains at its position
  - Stack size UNCHANGED (n consumed, copy added)
  - Net items: 5 → 5

OP_ROLL result: [ A, C, D, B ]
  - B (position 2) is MOVED to top
  - Original B is REMOVED from position 2
  - Stack COMPACTED
  - Net items: 5 → 4

Visualization Table

``` Operation | Effect on Target | Stack Size | Original Preserved?

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