StdHep is a binary format for the HEPEVT event generation format.
Most of the event generators on An Inventory of Event Generators for Linear Collider Physics can create StdHep files, write HEPEVT blocks that PYTHIA/cernlib can convert, or interface directly to PYTHIA.
The command /generator/filename is used to select a StdHep file.
/generator/filename events.stdhep
The equivalent command line switch is i, which also takes the name of the StdHep file.
slic -g mygeom.lcdd -i events.stdhep -r 1