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   tee    ( 2 )

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Имя (Name)

tee - duplicating pipe content

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Синопсис (Synopsis)

#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h>

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

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Описание (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 descriptor 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 bit mask that is composed by ORing together zero or more of the following values:

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 implemented in the future; see splice(2).

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

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Возвращаемое значение (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.

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Ошибки (Error)

EAGAIN SPLICE_F_NONBLOCK was specified in flags or one of the file descriptors had been marked as nonblocking (O_NONBLOCK), and the operation would block.

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.

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Версии (Versions)

The tee() system call first appeared in Linux 2.6.17; library support was added to glibc in version 2.5.

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Стандарты (Conforming to)

This system call is Linux-specific.

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Примечание (Note)

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

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Примеры (Examples)

The example below implements a basic tee(1) program using the
       tee() system call.  Here is an example of its use:

           $ date |./a.out out.log | cat
           Tue Oct 28 10:06:00 CET 2014
           $ cat out.log
           Tue Oct 28 10:06:00 CET 2014

   Program source

       #define _GNU_SOURCE
       #include <fcntl.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <errno.h>
       #include <limits.h>

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

           if (argc != 2) {
               fprintf(stderr, "Usage: %s <file>\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           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);
       }

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Смотри также (See also)

splice(2), vmsplice(2), pipe(7)

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