awk -F"\t" '                                                                    # start awk and define the field separator
NR == FNR       {INT[$1] = INT[$1] $2 "-" $3 FS                                 # for the first file, identified by total record No.
                                                                                # being equal to the file's NR, save intervals to an
                                                                                # array indexed by $1 as a list of L-R L-R L-R etc.
                 next                                                           # stop processing this line, start over with  next
                }
                                                                                # this is processed for second file only
                {split (INT[$1], T)                                             # split the interval list into individual L-R into
                                                                                # temp array T
                 OUT = "NA"                                                     # predefine OUT should no match be found
                 for (t in T)   {split (T[t], LM, "-")                          # loop across all individual L-R entries, split each 
                                                                                # one into limits array, with LM[1] holding L(eft)    
                                                                                # and LM[2] the R(ight) border
                                 if ($2 >= LM[1] && $2 < LM[2]) OUT = $4        # if $2 fits between limits, set OUT to $4
                                }
                 print OUT                                                      # and print it
                }
' file1 file2                                                                   # specify input files