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diff --git a/man2/tee.2 b/man2/tee.2 new file mode 100644 index 0000000..7a3a6b1 --- /dev/null +++ b/man2/tee.2 @@ -0,0 +1,199 @@ +.\" This manpage is Copyright (C) 2006 Jens Axboe +.\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH tee 2 2023-05-03 "Linux man-pages 6.05.01" +.SH NAME +tee \- duplicating pipe content +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" +.B #include <fcntl.h> +.PP +.BI "ssize_t tee(int " fd_in ", int " fd_out ", size_t " len \ +", unsigned int " flags ); +.fi +.\" Return type was long before glibc 2.7 +.SH DESCRIPTION +.\" Example programs http://brick.kernel.dk/snaps +.\" +.\" +.\" add a "tee(in, out1, out2)" system call that duplicates the pages +.\" (again, incrementing their reference count, not copying the data) from +.\" one pipe to two other pipes. +.BR tee () +duplicates up to +.I len +bytes of data from the pipe referred to by the file descriptor +.I fd_in +to the pipe referred to by the file descriptor +.IR fd_out . +It does not consume the data that is duplicated from +.IR fd_in ; +therefore, that data can be copied by a subsequent +.BR splice (2). +.PP +.I flags +is a bit mask that is composed by ORing together +zero or more of the following values: +.TP 1.9i +.B SPLICE_F_MOVE +Currently has no effect for +.BR tee (); +see +.BR splice (2). +.TP +.B SPLICE_F_NONBLOCK +Do not block on I/O; see +.BR splice (2) +for further details. +.TP +.B SPLICE_F_MORE +Currently has no effect for +.BR tee (), +but may be implemented in the future; see +.BR splice (2). +.TP +.B SPLICE_F_GIFT +Unused for +.BR tee (); +see +.BR vmsplice (2). +.SH RETURN VALUE +Upon successful completion, +.BR 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 +.IR fd_in . +.PP +On error, +.BR tee () +returns \-1 and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EAGAIN +.B SPLICE_F_NONBLOCK +was specified in +.I flags +or one of the file descriptors had been marked as nonblocking +.RB ( O_NONBLOCK ) , +and the operation would block. +.TP +.B EINVAL +.I fd_in +or +.I fd_out +does not refer to a pipe; or +.I fd_in +and +.I fd_out +refer to the same pipe. +.TP +.B ENOMEM +Out of memory. +.SH STANDARDS +Linux. +.SH HISTORY +Linux 2.6.17, +glibc 2.5. +.SH NOTES +Conceptually, +.BR tee () +copies the data between the two pipes. +In reality no real data copying takes place though: +under the covers, +.BR tee () +assigns data to the output by merely grabbing +a reference to the input. +.SH EXAMPLES +The example below implements a basic +.BR tee (1) +program using the +.BR tee () +system call. +Here is an example of its use: +.PP +.in +4n +.EX +$ \fBdate | ./a.out out.log | cat\fP +Tue Oct 28 10:06:00 CET 2014 +$ \fBcat out.log\fP +Tue Oct 28 10:06:00 CET 2014 +.EE +.in +.SS Program source +\& +.\" SRC BEGIN (tee.c) +.EX +#define _GNU_SOURCE +#include <errno.h> +#include <fcntl.h> +#include <limits.h> +#include <stdio.h> +#include <stdlib.h> +#include <unistd.h> +\& +int +main(int argc, char *argv[]) +{ + int fd; + ssize_t len, slen; +\& + if (argc != 2) { + fprintf(stderr, "Usage: %s <file>\en", argv[0]); + exit(EXIT_FAILURE); + } +\& + fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644); + if (fd == \-1) { + perror("open"); + exit(EXIT_FAILURE); + } +\& + for (;;) { + /* + * 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); + } + 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"); + exit(EXIT_FAILURE); + } + len \-= slen; + } + } +\& + close(fd); + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SH SEE ALSO +.BR splice (2), +.BR vmsplice (2), +.BR pipe (7) |