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4 .\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
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26 .TH TEE 2 2009-09-15 "Linux" "Linux Programmer's Manual"
28 tee \- duplicating pipe content
31 .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
34 .BI "ssize_t tee(int " fd_in ", int " fd_out ", size_t " len \
35 ", unsigned int " flags );
37 .\" Return type was long before glibc 2.7
39 .\" Example programs http://brick.kernel.dk/snaps
42 .\" add a "tee(in, out1, out2)" system call that duplicates the pages
43 .\" (again, incrementing their reference count, not copying the data) from
44 .\" one pipe to two other pipes.
48 bytes of data from the pipe referred to by the file descriptor
50 to the pipe referred to by the file descriptor
52 It does not consume the data that is duplicated from
54 therefore, that data can be copied by a subsequent
58 is a series of modifier flags, which share the name space with
64 Currently has no effect for
70 Do not block on I/O; see
75 Currently has no effect for
77 but may be implemented in the future; see
86 Upon successful completion,
88 returns the number of bytes that were duplicated between the input
90 A return value of 0 means that there was no data to transfer,
91 and it would not make sense to block, because there are no
92 writers connected to the write end of the pipe referred to by
99 is set to indicate the error.
106 does not refer to a pipe; or
110 refer to the same pipe.
117 system call first appeared in Linux 2.6.17.
119 This system call is Linux-specific.
123 copies the data between the two pipes.
124 In reality no real data copying takes place though:
127 assigns data in the output by merely grabbing
128 a reference to the input.
130 The following example implements a basic
146 main(int argc, char *argv[])
152 fprintf(stderr, "Usage: %s <file>\\n", argv[0]);
156 fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644);
164 * tee stdin to stdout.
166 len = tee(STDIN_FILENO, STDOUT_FILENO,
167 INT_MAX, SPLICE_F_NONBLOCK);
179 * Consume stdin by splicing it to a file.
182 slen = splice(STDIN_FILENO, NULL, fd, NULL,