bx fetch header

Get the block header from the specified hash or height. Height is ignored if both are specified.

$ bx fetch-header --help

Usage: bx fetch-header [-h] [--config value] [--format value] [--hash
value] [--height value]

Info: Get the block header from the specified hash or height. Height is
ignored if both are specified. Requires a Libbitcoin server connection.

Options (named):

-c [--config]        The path to the configuration settings file.
-f [--format]        The output format. Options are 'info', 'json' and
                     'xml', defaults to 'info'.
-h [--help]          Get a description and instructions for this command.
-s [--hash]          The Base16 block hash.
-t [--height]        The block height.

This command supports configuration settings.

Example 1

--height 0

$ bx fetch-header

header
{
    bits 486604799
    hash 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
    merkle_root 4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b
    nonce 2083236893
    previous_block_hash 0000000000000000000000000000000000000000000000000000000000000000
    time_stamp 1231006505
    version 1
}

Example 2

--height 1

$ bx fetch-header -t 1

header
{
    bits 486604799
    hash 00000000839a8e6886ab5951d76f411475428afc90947ee320161bbf18eb6048
    merkle_root 0e3e2357e806b6cdb1f70b54c3a3a17b6714ee1f0e68bebb44a74b1efd512098
    nonce 2573394689
    previous_block_hash 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
    time_stamp 1231469665
    version 1
}

Notice that the header.previous_block_hash property matches the header.hash property returned for the height 0 request.

Example 3

--hash [genesis block hash]

$ bx fetch-header -s 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

header
{
    bits 486604799
    hash 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
    merkle_root 4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b
    nonce 2083236893
    previous_block_hash 0000000000000000000000000000000000000000000000000000000000000000
    time_stamp 1231006505
    version 1
}

Example 4

--height 1 --hash [genesis block hash]

$ bx fetch-header -t 1 -s 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

header
{
    bits 486604799
    hash 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
    merkle_root 4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b
    nonce 2083236893
    previous_block_hash 0000000000000000000000000000000000000000000000000000000000000000
    time_stamp 1231006505
    version 1
}

The genesis block is height 0. Notice that height is ignored when both hash and height are specified. To test a height against a hash request the hash based on height alone and then compare the hash value against the returned header.hash property.