Dear Enric,
lb-run sets the environment (PATH, PYTHONPATH, LD_LIBRARYPATH etc) for a specific part of the LHCb software and then executes a program. That’s why it usually comes with many arguments. It is put in the path by the aforementioned login script.
source /cvmfs/lhcb.cern.ch/group_login.sh
which lb-run
/cvmfs/lhcb.cern.ch/lib/lhcb/LBSCRIPTS/LBSCRIPTS_v9r2p6/InstallArea/scripts/lb-run
Hope this helps,
Albert