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StackBasedScriptingLanguage

Implementation of stack based scripting language for validation of transactions(clearing)

Constants

Word Opcode Hex Input Output Description
OP_0, OP_FALSE 0 0x00 Nothing. (empty value) An empty array of bytes is pushed onto the stack. (This is not a no-op: an item is added to the stack.)
N/A 1-75 0x01-0x4b (special) data The next opcode bytes is data to be pushed onto the stack
OP_PUSHDATA1 76 0x4c (special) data The next byte contains the number of bytes to be pushed onto the stack.
OP_PUSHDATA2 77 0x4d (special) data The next two bytes contain the number of bytes to be pushed onto the stack in little endian order.
OP_PUSHDATA4 78 0x4e (special) data The next four bytes contain the number of bytes to be pushed onto the stack in little endian order.
OP_1NEGATE 79 0x4f Nothing. -1 The number -1 is pushed onto the stack.
OP_1, OP_TRUE 81 0x51 Nothing. 1 The number 1 is pushed onto the stack.
OP_2-OP_16 82-96 0x52-0x60 Nothing. 2-16 The number in the word name (2-16) is pushed onto the stack.

Flow control

Word Opcode Hex Input Output Description
OP_NOP 97 0x61 Nothing Nothing Does nothing.
OP_IF 99 0x63 if [statements] [else [statements]]* endif if [statements] [else [statements]]* endif If the top stack value is not False, the statements are executed. The top stack value is removed.
OP_NOTIF 100 0x64 notif [statements] [else [statements]]* endif notif [statements] [else [statements]]* endif If the top stack value is False, the statements are executed. The top stack value is removed.
OP_ELSE 103 0x67 if [statements] [else [statements]]* endif if [statements] [else [statements]]* endif If the preceding OP_IF or OP_NOTIF or OP_ELSE was not executed then these statements are and if the preceding OP_IF or OP_NOTIF or OP_ELSE was executed then these statements are not.
OP_ENDIF 104 0x68 if [statements] [else [statements]]* endif if [statements] [else [statements]]* endif Ends an if/else block. All blocks must end, or the transaction is invalid. An OP_ENDIF without OP_IF earlier is also invalid.
OP_VERIFY 105 0x69 True / false Nothing / fail Marks transaction as invalid if top stack value is not true. The top stack value is removed.
OP_RETURN 106 0x6a Nothing fail Marks transaction as invalid. Since bitcoin 0.9, a standard way of attaching extra data to transactions is to add a zero-value output with a scriptPubKey consisting of OP_RETURN followed by data. Such outputs are provably unspendable and specially discarded from storage in the UTXO set, reducing their cost to the network. Since 0.12, standard relay rules allow a single output with OP_RETURN, that contains any sequence of push statements (or OP_RESERVED[1]) after the OP_RETURN provided the total scriptPubKey length is at most 83 bytes.

Stack

Word Opcode Hex Input Output Description
OP_TOALTSTACK 107 0x6b x1 (alt)x1 Puts the input onto the top of the alt stack. Removes it from the main stack.
OP_FROMALTSTACK 108 0x6c (alt)x1 x1 Puts the input onto the top of the main stack. Removes it from the alt stack.
OP_IFDUP 115 0x73 x x / x x If the top stack value is not 0, duplicate it.
OP_DEPTH 116 0x74 Nothing Puts the number of stack items onto the stack.
OP_DROP 117 0x75 x Nothing Removes the top stack item.
OP_DUP 118 0x76 x x x Duplicates the top stack item.
OP_NIP 119 0x77 x1 x2 x2 Removes the second-to-top stack item.
OP_OVER 120 0x78 x1 x2 x1 x2 x1 Copies the second-to-top stack item to the top.
OP_PICK 121 0x79 xn ... x2 x1 x0 xn ... x2 x1 x0 xn The item n back in the stack is copied to the top.
OP_ROLL 122 0x7a xn ... x2 x1 x0 ... x2 x1 x0 xn The item n back in the stack is moved to the top.
OP_ROT 123 0x7b x1 x2 x3 x2 x3 x1 The top three items on the stack are rotated to the left.
OP_SWAP 124 0x7c x1 x2 x2 x1 The top two items on the stack are swapped.
OP_TUCK 125 0x7d x1 x2 x2 x1 x2 The item at the top of the stack is copied and inserted before the second-to-top item.
OP_2DROP 109 0x6d x1 x2 Nothing Removes the top two stack items.
OP_2DUP 110 0x6e x1 x2 x1 x2 x1 x2 Duplicates the top two stack items.
OP_3DUP 111 0x6f x1 x2 x3 x1 x2 x3 x1 x2 x3 Duplicates the top three stack items.
OP_2OVER 112 0x70 x1 x2 x3 x4 x1 x2 x3 x4 x1 x2 Copies the pair of items two spaces back in the stack to the front.
OP_2ROT 113 0x71 x1 x2 x3 x4 x5 x6 x3 x4 x5 x6 x1 x2 The fifth and sixth items back are moved to the top of the stack.
OP_2SWAP 114 0x72 x1 x2 x3 x4 x3 x4 x1 x2 Swaps the top two pairs of items.