Captures

Captures pull data out of a command's executed transaction into script variables: its hash ($>, $*>), events it emitted (->), or the error it reverted with (-!>).

Event Captures

The exec command can capture events emitted by the transaction with ->:

exec 0x44fA8E6f47987339850636F88629646662444217 "createPool(address,uint24)" @token(DAI) 3000 -> Transfer [_ $pool]

The destructure list binds event arguments positionally; use _ to skip one.

Error Captures

Use -!> to catch and decode transaction reverts. After the error name you can add a destructure ([...]), a boolean variable ($var), or nothing:

set $c 0x44fA8E6f47987339850636F88629646662444217

# Assert a specific error (no data captured)
exec $c "deny()" -!> Unauthorized()

# Destructure error arguments into variables
exec $c "withdraw(uint256)" 200 -!> InsufficientBalance(uint256,uint256) [$balance $required]

# Catch a require/revert reason
exec $c "transfer(address,uint256)" @me 100e18 -!> Error(string) [$reason]

# Boolean variable — $e is "true" if error matched
exec $c "deny()" -!> Unauthorized() $e

# Generic catch-all (no error name)
exec $c "doSomething()" -!> [$reason]
exec $c "doSomething()" -!> $e

Use -?!> if the error is optional (transaction may or may not revert). With a boolean variable, $e is "true" on match, "false" on success or mismatched error:

set $c 0x44fA8E6f47987339850636F88629646662444217

exec $c "maybeRevert()" -?!> Error(string) [$reason]
exec $c "maybeRevert()" -?!> Unauthorized() $e

Supported error types:

• Custom named errors: revert CustomError(arg1, arg2)
• Error(string): require(cond, "msg") / revert("msg")
• Panic(uint256): assert(cond) failures
• Empty reverts: pre-0.4.22 revert() with no data

Transaction Hash Captures

Redirect a command's transaction hash into a variable with $>:

exec @token(DAI) "transfer(address,uint256)" @me 1e18 $> $tx

$> $var binds the hash of the command's last transaction — the primary one. Compound commands may send prerequisite transactions first (an approve, an ENS commit), and whether they do can vary between runs, so the last hash is the stable notion of "the command's transaction".

When you want every hash, $*> $var binds them all as an array, newest last:

load ens
ens:register myname.eth @me 1y $*> $txs

There is deliberately no positional destructuring for tx hashes: because prerequisite transactions are conditional, a fixed-count pattern would bind different transactions on different runs.

Both forms compose with the explorer module ⚗️ — capture the hash, then read anything about it:

load explorer
exec @token(DAI) "transfer(address,uint256)" @me 1e18 $> $tx
print @explorer:tx($tx)
print @explorer:tx.fee($tx)

Tx captures can be combined with event captures (the transactions execute once, serving both) but not with error captures — a reverted transaction has no meaningful hash to capture.

Like all captures, they need an execution context (an interactive run or a sim:fork block); validating or previewing a script does not execute transactions, so there is nothing to capture.

Captures on Batches

All capture forms also work on a whole batch block, which executes as a single transaction — so $> $tx on a batch binds one hash for the whole bundle. See Blocks & Batching.

Event and tx captures also work on if/loop blocks and def commands: the inner transactions execute inside the block exactly once, and the capture reads their receipts. Error captures are the exception — an inner revert aborts the block before the capture could observe it, so put -!> on the inner command instead.