pattern_locate Subroutine

    subroutine pattern_locate(lstring, lpattern, number_hits, hit_loc)
    !---------------------------------------------------------------------------
    ! Locates all instances of a PATTERN in STRING, placing the location of
    ! the beginning of the pattern in hit_loc.
    !---------------------------------------------------------------------------

    ! arguments
    character(len=*), intent(in   ) :: lstring
    character(len=*), intent(in   ) :: lpattern
    integer,          intent(inout) :: number_hits
    integer,          intent(inout) :: hit_loc(:)
    
    ! local variables
    integer :: k, klast, ncount
    integer :: len_string, len_pattern

    ! initialize variables
    ncount = 0
    len_string = len(lstring)
    len_pattern = len(  trim(adjustL(lpattern) ))

    !---------------------------------------------------------------------------
    ! error check - conduct the search only if the pattern & string are not empty
    !---------------------------------------------------------------------------
    if( (len_pattern > 0) .and. (len_string > 0) ) then
       klast = 0
       !------------------------------------------------------------------------
       ! examine the string to find the find the FIRST instance of the pattern
       !------------------------------------------------------------------------
       k = index(lstring(klast+1:len_string), trim(adjustL(lpattern) ))

       do while( k > 0 )
          !---------------------------------------------------------------------
          ! if index is nonzero, there is at least one match, increment
          ! through the string checking for additional matches.
          !---------------------------------------------------------------------
          ncount = ncount + 1      ! count match
          klast = k + klast        ! slide forward in string looking for next match
          hit_loc(ncount) = klast  ! save location of the pattern match
          k = index(lstring(klast+1:len_string),  trim(adjustL(lpattern) ))
       enddo     ! while
    endif
    ! if they do not agree something has failed.
    if (number_hits /= ncount) ncount = 0
    ! return value
    number_hits = ncount

    !---------------------------------------------------------------------------
    end subroutine pattern_locate