ios.isatty   → true or false
ios.tty?     → true or false

Returns true if ios is associated with a terminal device (tty), false otherwise.

File.new("testfile").isatty   #=> false
File.new("/dev/tty").isatty   #=> true

Source Code

/*
*  call-seq:
*     ios.isatty   => true or false
*     ios.tty?     => true or false
*  
*  Returns <code>true</code> if <em>ios</em> is associated with a
*  terminal device (tty), <code>false</code> otherwise.
*     
*     File.new("testfile").isatty   #=> false
*     File.new("/dev/tty").isatty   #=> true
*/

static VALUE
rb_io_isatty(io)
   VALUE io;
{
   OpenFile *fptr;

   GetOpenFile(io, fptr);
   if (isatty(fileno(fptr->f)) == 0)
       return Qfalse;
   return Qtrue;
}