TEE(2)			   Linux Programmers Manual		       TEE(2)



NAME
       tee - duplicating pipe content

SYNOPSIS
       #define _GNU_SOURCE
       #include 

       long tee(int fd_in, int fd_out, size_t len, unsigned int flags);

DESCRIPTION
       tee()  duplicates  up to len bytes of data from the pipe referred to by
       the file descriptor fd_in to the pipe referred to by the file  descrip
       tor  fd_out.   It  does	not  consume  the data that is duplicated from
       fd_in; therefore, that data can be copied by a subsequent splice(2).

       flags is a series of modifier flags, which share the  name  space  with
       splice(2) and vmsplice(2):

       SPLICE_F_MOVE	  Currently has no effect for tee(); see splice(2).

       SPLICE_F_NONBLOCK  Do  not  block  on  I/O;  see  splice(2) for further
			  details.

       SPLICE_F_MORE	  Currently has no effect for tee(), but may be imple
			  mented in the future; see splice(2).

       SPLICE_F_GIFT	  Unused for tee(); see vmsplice(2).

RETURN VALUE
       Upon successful completion, tee() returns the number of bytes that were
       duplicated between the input and output.  A return  value  of  0  means
       that  there  was  no  data  to transfer, and it would not make sense to
       block, because there are no writers connected to the write end  of  the
       pipe referred to by fd_in.

       On error, tee() returns -1 and errno is set to indicate the error.

ERRORS
       EINVAL fd_in  or  fd_out  does not refer to a pipe; or fd_in and fd_out
	      refer to the same pipe.

       ENOMEM Out of memory.

VERSIONS
       The tee() system call first appeared in Linux 2.6.17.

CONFORMING TO
       This system call is Linux-specific.

NOTES
       Conceptually, tee() copies the data between the two pipes.  In  reality
       no  real  data  copying	takes  place  though:  under the covers, tee()
       assigns data in the output by merely grabbing a reference to the input.

EXAMPLE
       The following example implements a basic tee(1) program using the tee()
       system call.

       #define _GNU_SOURCE
       #include 
       #include 
       #include 
       #include 
       #include 
       #include 
       #include 

       int
       main(int argc, char *argv[])
       {
	   int fd;
	   int len, slen;

	   assert(argc == 2);

	   fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644);
	   if (fd == -1) {
	       perror("open");
	       exit(EXIT_FAILURE);
	   }

	   do {
	       /*
		* tee stdin to stdout.
		*/
	       len = tee(STDIN_FILENO, STDOUT_FILENO,
			 INT_MAX, SPLICE_F_NONBLOCK);

	       if (len < 0) {
		   if (errno == EAGAIN)
		       continue;
		   perror("tee");
		   exit(EXIT_FAILURE);
	       } else
		   if (len == 0)
		       break;

	       /*
		* Consume stdin by splicing it to a file.
		*/
	       while (len > 0) {
		   slen = splice(STDIN_FILENO, NULL, fd, NULL,
				 len, SPLICE_F_MOVE);
		   if (slen < 0) {
		       perror("splice");
		       break;
		   }
		   len -= slen;
	       }
	   } while (1);

	   close(fd);
	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       splice(2), vmsplice(2), feature_test_macros(7)

COLOPHON
       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux				  2006-04-28				TEE(2)