C*GRGENV -- get value of PGPLOT environment parameter (MAC)
C+
      SUBROUTINE GRGENV(NAME, VALUE, L)
      CHARACTER*(*) NAME, VALUE
      INTEGER L
C
C Return the value of a PGPLOT environment parameter. In Sun/Convex-UNIX,
C environment parameters are UNIX environment variables; e.g. parameter
C ENVOPT is environment variable PGPLOT_ENVOPT. Translation is not
C recursive and is case-sensitive.
C
C Arguments:
C  NAME   : (input) the name of the parameter to evaluate.
C  VALUE  : receives the value of the parameter, truncated or extended
C           with blanks as necessary. If the parameter is undefined,
C           a blank string is returned.
C  L      : receives the number of characters in VALUE, excluding
C           trailing blanks. If the parameter is undefined, zero is
C           returned.
C
C On Macintosh, the environment variables are stored in file.  This subroutine
C first looks for the file PGPLOTENVNAMES, in the application directory.
C If it can't be found, a standard file dialog box will be displayed,
C so that you can find the file.  Once it is found, the name and location are 
C stored so that you will not be prompted again.  
C-- 
C 19-Jan-1988
C 25-Sep-1995  Modified to work on mac with MPW Fortran 2.1.  All environment 
C              parameters are stored in the file.  The file can have any name 
C              but best thing to do is to put a file called pgplotenvnames
C              in the application directory. See Tech. Note 35 for more information
C              about Macintosh file system.  Note: this subroutine
C              needs to be compiled with the -u switch to initialize volrefnum 
C              to zero, since a value less than zero specifies a folder.
C-----------------------------------------------------------------------       
      INTEGER LIN, LUN,LStart,VolRefNum, JVRefNum
      CHARACTER*32 TEST, Line*120, FilNam*120
	  External JVRefNum
	  Save FileName,VolRefNum
	  
C
      TEST = 'PGPLOT_'//NAME
      LIN = INDEX(TEST, ' ')-1
	  Value = ' '
	  L = 0
	  Call GrgLun(LUN)

C  If volume reference number has been set, switch to that volume.  The
C  first time grgenv is called, volrefnum will not be set and the current
C  directory is the application directory.  The volume reference number will
C  be set after pgplotenvnames is found.
	  If (VolRefNum .lt. 0) Then
	     Call  F_SETVOLUME(VolRefNum)
	  End If

C  Try to open FilNam.  The first time that Grgenv is called Filnam will
C  be empty and the open will fail.  So try to open pgplotenvnames in the
C  current directory.  If that fails put up a standard file dialog box to
C  find pgplotenvnames.  If FilNam has been set then after assigning a 
C  unit number to the file reset the volume reference number to the application
C  directory.  
	  Open(Unit = lun,File=FilNam,Status='OLD',Err = 10,Readonly)
	  Call F_SETVOLUME(JVREFNUM(-1))
	  Go to 1
	  
10    Open(Unit = lun,File='pgplotenvnames',Status='OLD',Err = 20,Readonly)
      FilNam = 'pgplotenvnames'
	  VolRefNum = JVREFNUM(Lun)
      Go to 1

C Put up standard file dialog box.  Once found store the file name and volume
C reference number.
20    CALL GRWARN('Could not find file PGPLOTENVNAMES in current directory.')
      CALL GRWARN('A dialog box will come up allowing you to find the file with the')
      CALL GRWARN('environment variables. Hit return for the dialog box to appear.')
      Pause
      Open(Unit=lun,File=*,STATUS='OLD',err=100,Readonly)
      Inquire(Unit=LUN,Name=FilNam)
	  VolRefNum = JVREFNUM(Lun)

C File has been found, so search for environmental variable and extract value.
1     Continue
	     Read(Lun,'(A512)',End=2) Line 
	     If (Test(:Lin) .EQ. Line(:Lin)) Then
	        Lstart = index(Line,"'")+1
	        L = index(Line(Lstart:),"'")-1
	        Value = Line(LStart:LStart+L-1)
			Close(Lun)
	        Go to 2
	     End If
	  Go to 1
2     Close(LUN)
      Return
	     

C     Could not find PGPLOTENVNAMES.
100   Close(LUN)
      CALL GRWARN('Cancelled dialog box to find PGPLOTENVNAMES')
      Return
      END