subroutine openn(UNIT,ENVcod)
c
c    Associate a file specified by ENVcod with a Fortran UNIT number.
c    ENVcod is assumed to lie between 0 and 9 inclusive.
c    ENVcod = 0 specifies the character card(s), assumed to reside in
c    the file whose name is the value of the environment variable CHARCARD.
c    ENVcod = i specifies the file whose name is the value of the environment
c    variable FILEi.
c
        integer UNIT, ENVcod 
        character null
        character*50 getenv, value
        parameter (null = '\0')
        integer ichar
        character char
        if (ENVcod .eq. 0) then
                value = getenv( 'CHARCARD' )
        else if (ENVcod .eq. 1) then
                value = getenv ( 'FILE1' )
        else if (ENVcod .eq. 2) then
                value = getenv ( 'FILE2' )
        else if (ENVcod .eq. 3) then
                value = getenv ( 'FILE3' )
        else if (ENVcod .eq. 4) then
                value = getenv ( 'FILE4' )
        else if (ENVcod .eq. 5) then
                value = getenv ( 'FILE5' )
        else if (ENVcod .eq. 6) then
                value = getenv ( 'FILE6' )
        else if (ENVcod .eq. 7) then
                value = getenv ( 'FILE7' )
        else if (ENVcod .eq. 8) then
                value = getenv ( 'FILE8' )
        else if (ENVcod .eq. 9) then
                value = getenv ( 'FILE9' )
        else
                print*, "(openn) ENVcod =", ENVcod, "out of range"
                stop
        endif
        if (value(1:1) .eq. null) then
                print*, '(openn) environment variable',
     $             'FILE'//char(ichar('0')+ENVcod), ' is undefined'
                stop
        endif
        open( UNIT , file = value )
        rewind UNIT
        return
        end