' Reads the '.mmbasic-shell' file.
'
' @param  exist%  If 1 then ERROR if file does not exist, otherwise return empty string.
' @param  fnbr%   File number to use for accessing the file, if unspecified/0 then uses #9.
' @return         The contents of the first line of the file.
Function sys.read_shell_file$(exist%, fnbr%)
 Const f$ = sys.HOME$() + "/.mmbasic-shell"
 If Not exist% And Not Mm.Info(Exists f$) Then Exit Function
 Const _fnbr% = Choice(fnbr%, fnbr%, 9)
 Open f$ For Input As _fnbr%
 Line Input #_fnbr%, sys.read_shell_file$
 Close _fnbr%
End Function

' Writes the '.mmbasic-shell' file for later reading by sys.run_shell().
'
' @param  s$     Contents to write to the file, if empty then writes path of current program.
' @param  fnbr%  File number to use for accessing the file, if unspecified/0 then uses #9.
Sub sys.write_shell_file(s$, fnbr%)
 Const f$ = sys.HOME$() + "/.mmbasic-shell"
 Const _s$ = Choice(s$ = "", Mm.Info(Current), s$)
 Const _fnbr% = Choice(fnbr%, fnbr%, 9)
 If sys.read_shell_file$(0, _fnbr%) <> _s$ Then
   ' Only write if content has changed.
   Open f$ For Output As _fnbr%
   Print #_fnbr%, _s$
   Close _fnbr%
 EndIf
End Sub

' Runs the program specified by the '.mmbasic-shell' file.
'
' @param  fnbr%  File number to use for accessing the file, if unspecified/0 then uses #9.
Sub sys.run_shell(fnbr%)
 Const prog$ = sys.read_shell_file$(1, fnbr%)
 If prog$ <> "" Then Run prog$
End Sub