SHACKLOG currently does not directly support ADIF. However, you can export either your entire log, or portions of it (eg the results of a SEARCH), and then convert the exported file to ADIF, using the PROADIKON program by DL9HO, which at the time of writing is freeware. There is a 25 QSO limit on unregistered copies but registration is free.

Alternatively, you can use BV7 by DF3CB, also free of charge at the time of writing. BV7 will import CSV files in a user defined format and will not only convert them to ADIF, it also provides a complete QSL management and label printing facility.