Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

tee(2) [linux man page]

TEE(2)							     Linux Programmer's Manual							    TEE(2)

NAME
tee - duplicating pipe content SYNOPSIS
#define _GNU_SOURCE #include <fcntl.h> ssize_t 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 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 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 implemented 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 <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> ", 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); } SEE ALSO
splice(2), vmsplice(2), feature_test_macros(7) COLOPHON
This page is part of release 3.27 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 2009-09-15 TEE(2)

Check Out this Related Man Page

SPLICE(2)						     Linux Programmer's Manual							 SPLICE(2)

NAME
splice - splice data to/from a pipe SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> ssize_t splice(int fd_in, loff_t *off_in, int fd_out, loff_t *off_out, size_t len, unsigned int flags); DESCRIPTION
splice() moves data between two file descriptors without copying between kernel address space and user address space. It transfers up to len bytes of data from the file descriptor fd_in to the file descriptor fd_out, where one of the descriptors must refer to a pipe. If fd_in refers to a pipe, then off_in must be NULL. If fd_in does not refer to a pipe and off_in is NULL, then bytes are read from fd_in starting from the current file offset, and the current file offset is adjusted appropriately. If fd_in does not refer to a pipe and off_in is not NULL, then off_in must point to a buffer which specifies the starting offset from which bytes will be read from fd_in; in this case, the current file offset of fd_in is not changed. Analogous statements apply for fd_out and off_out. The flags argument is a bit mask that is composed by ORing together zero or more of the following values: SPLICE_F_MOVE Attempt to move pages instead of copying. This is only a hint to the kernel: pages may still be copied if the kernel cannot move the pages from the pipe, or if the pipe buffers don't refer to full pages. The initial implementation of this flag was buggy: therefore starting in Linux 2.6.21 it is a no-op (but is still permitted in a splice() call); in the future, a correct implementation may be restored. SPLICE_F_NONBLOCK Do not block on I/O. This makes the splice pipe operations nonblocking, but splice() may nevertheless block because the file descriptors that are spliced to/from may block (unless they have the O_NONBLOCK flag set). SPLICE_F_MORE More data will be coming in a subsequent splice. This is a helpful hint when the fd_out refers to a socket (see also the description of MSG_MORE in send(2), and the description of TCP_CORK in tcp(7)) SPLICE_F_GIFT Unused for splice(); see vmsplice(2). RETURN VALUE
Upon successful completion, splice() returns the number of bytes spliced to or from the pipe. 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, splice() returns -1 and errno is set to indicate the error. ERRORS
EBADF One or both file descriptors are not valid, or do not have proper read-write mode. EINVAL Target file system doesn't support splicing; target file is opened in append mode; neither of the descriptors refers to a pipe; or offset given for nonseekable device. ENOMEM Out of memory. ESPIPE Either off_in or off_out was not NULL, but the corresponding file descriptor refers to a pipe. VERSIONS
The splice() system call first appeared in Linux 2.6.17; library support was added to glibc in version 2.5. CONFORMING TO
This system call is Linux-specific. NOTES
The three system calls splice(), vmsplice(2), and tee(2), provide user-space programs with full control over an arbitrary kernel buffer, implemented within the kernel using the same type of buffer that is used for a pipe. In overview, these system calls perform the following tasks: splice() moves data from the buffer to an arbitrary file descriptor, or vice versa, or from one buffer to another. tee(2) "copies" the data from one buffer to another. vmsplice(2) "copies" data from user space into the buffer. Though we talk of copying, actual copies are generally avoided. The kernel does this by implementing a pipe buffer as a set of reference- counted pointers to pages of kernel memory. The kernel creates "copies" of pages in a buffer by creating new pointers (for the output buf- fer) referring to the pages, and increasing the reference counts for the pages: only pointers are copied, not the pages of the buffer. EXAMPLE
See tee(2). SEE ALSO
sendfile(2), tee(2), vmsplice(2) COLOPHON
This page is part of release 3.53 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 2012-05-04 SPLICE(2)
Man Page

Featured Tech Videos