gpg-preset-passphrase is invoked this way:
gpg-preset-passphrase [options] [command] cacheid
cacheid is either a 40 character keygrip of hexadecimal
characters identifying the key for which the passphrase should be set
or cleared. The keygrip is listed along with the key when running the
gpgsm --dump-secret-keys. Alternatively an arbitrary
string may be used to identify a passphrase; it is suggested that such
a string is prefixed with the name of the application (e.g
One of the following command options must be given:
Preset a passphrase. This is what you usually will
gpg-preset-passphrase will then read the passphrase from
Flush the passphrase for the given cache ID from the cache.
The following additional options may be used:
Output additional information while running.
Instead of reading the passphrase from
stdin, use the supplied
string as passphrase. Note that this makes the passphrase visible
for other users.