All opcodes are declared in the script.h file in the Bitcoin reference client source code.
A description of the most commonly used opcodes is listed here. This table is taken from the Bitcoin developer's guide:
Opcode |
Description |
OP_CHECKSIG |
This takes a public key and signature and validates the signature of the hash of the transaction. If it matches, then TRUE is pushed onto the stack; otherwise, FALSE is pushed. |
OP_EQUAL |
This returns 1 if the inputs are exactly equal; otherwise, 0 is returned. |
OP_DUP |
This duplicates the top item in the stack. ... |