ios.reopen(other_IO)         → ios 
ios.reopen(path, mode_str)   → ios

Reassociates ios with the I/O stream given in other_IO or to a new stream opened on path. This may dynamically change the actual class of this stream.

f1 = File.new("testfile")
f2 = File.new("testfile")
f2.readlines[0]   #=> "This is line one\n"
f2.reopen(f1)     #=> #<file:testfile>
f2.readlines[0]   #=> "This is line one\n"</file:testfile>

Source Code

/*
*  call-seq:
*     ios.reopen(other_IO)         => ios 
*     ios.reopen(path, mode_str)   => ios
*  
*  Reassociates <em>ios</em> with the I/O stream given in
*  <i>other_IO</i> or to a new stream opened on <i>path</i>. This may
*  dynamically change the actual class of this stream.
*     
*     f1 = File.new("testfile")
*     f2 = File.new("testfile")
*     f2.readlines[0]   #=> "This is line one\n"
*     f2.reopen(f1)     #=> #<File:testfile>
*     f2.readlines[0]   #=> "This is line one\n"
*/

static VALUE
rb_io_reopen(argc, argv, file)
   int argc;
   VALUE *argv;
   VALUE file;
{
   VALUE fname, nmode;
   char *mode;
   OpenFile *fptr;

   rb_secure(4);
   if (rb_scan_args(argc, argv, "11", &fname, &nmode) == 1) {
       VALUE tmp = rb_io_check_io(fname);
       if (!NIL_P(tmp)) {
           return io_reopen(file, tmp);
       }
   }

   SafeStringValue(fname);
   rb_io_taint_check(file);
   fptr = RFILE(file)->fptr;
   if (!fptr) {
       fptr = RFILE(file)->fptr = ALLOC(OpenFile);
       MEMZERO(fptr, OpenFile, 1);
   }

   if (!NIL_P(nmode)) {
       fptr->mode = rb_io_mode_flags(StringValuePtr(nmode));
   }

   if (fptr->path) {
       free(fptr->path);
       fptr->path = 0;
   }

   fptr->path = strdup(RSTRING(fname)->ptr);
   mode = rb_io_flags_mode(fptr->mode);
   if (!fptr->f) {
       fptr->f = rb_fopen(fptr->path, mode);
       if (fptr->f2) {
           fclose(fptr->f2);
           fptr->f2 = 0;
       }
       return file;
   }

   if (freopen(RSTRING(fname)->ptr, mode, fptr->f) == 0) {
       rb_sys_fail(fptr->path);
   }
#ifdef USE_SETVBUF
   if (setvbuf(fptr->f, NULL, _IOFBF, 0) != 0)
       rb_warn("setvbuf() can't be honoured for %s", RSTRING(fname)->ptr);
#endif

   if (fptr->f2) {
       if (freopen(RSTRING(fname)->ptr, "w", fptr->f2) == 0) {
           rb_sys_fail(fptr->path);
       }
   }

   return file;
}