use Devel::Peek;

my $s = "30.31.force.0.5.1LGY.pdb";
Dump $s;
print 0+$s, "\n";  # treat as number
Dump $s;

__END__
SV = PV(0x605150) at 0x604fa0
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK)
  PV = 0x6370d0 "30.31.force.0.5.1LGY.pdb"\0
  CUR = 24
  LEN = 32
30.31
SV = PVNV(0x607880) at 0x604fa0
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,NOK,POK,pIOK,pNOK,pPOK)
  IV = 30       <---
  NV = 30.31    <---
  PV = 0x6370d0 "30.31.force.0.5.1LGY.pdb"\0
  CUR = 24
  LEN = 32