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1 | .\" Hey Emacs! This file is -*- nroff -*- source. |
2 | .\" | |
3 | .\" This manpage is Copyright (C) 2006 Jens Axboe | |
c11b1abf | 4 | .\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> |
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5 | .\" |
6 | .\" Permission is granted to make and distribute verbatim copies of this | |
7 | .\" manual provided the copyright notice and this permission notice are | |
8 | .\" preserved on all copies. | |
9 | .\" | |
10 | .\" Permission is granted to copy and distribute modified versions of this | |
11 | .\" manual under the conditions for verbatim copying, provided that the | |
12 | .\" entire resulting derived work is distributed under the terms of a | |
13 | .\" permission notice identical to this one. | |
c13182ef | 14 | .\" |
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15 | .\" Since the Linux kernel and libraries are constantly changing, this |
16 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
17 | .\" responsibility for errors or omissions, or for damages resulting from | |
18 | .\" the use of the information contained herein. The author(s) may not | |
19 | .\" have taken the same level of care in the production of this manual, | |
20 | .\" which is licensed free of charge, as they might when working | |
21 | .\" professionally. | |
c13182ef | 22 | .\" |
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23 | .\" Formatted or processed versions of this manual, if unaccompanied by |
24 | .\" the source, must acknowledge the copyright and authors of this work. | |
25 | .\" | |
52520fb5 | 26 | .TH TEE 2 2009-09-15 "Linux" "Linux Programmer's Manual" |
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27 | .SH NAME |
28 | tee \- duplicating pipe content | |
29 | .SH SYNOPSIS | |
30 | .nf | |
31 | .B #define _GNU_SOURCE | |
32 | .B #include <fcntl.h> | |
33 | ||
52520fb5 | 34 | .BI "ssize_t tee(int " fd_in ", int " fd_out ", size_t " len \ |
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35 | ", unsigned int " flags ); |
36 | .fi | |
52520fb5 | 37 | .\" Return type was long before glibc 2.7 |
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38 | .SH DESCRIPTION |
39 | .\" Example programs http://brick.kernel.dk/snaps | |
40 | .\" | |
41 | .\" | |
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42 | .\" add a "tee(in, out1, out2)" system call that duplicates the pages |
43 | .\" (again, incrementing their reference count, not copying the data) from | |
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44 | .\" one pipe to two other pipes. |
45 | .BR tee () | |
46 | duplicates up to | |
47 | .I len | |
48 | bytes of data from the pipe referred to by the file descriptor | |
49 | .I fd_in | |
50 | to the pipe referred to by the file descriptor | |
51 | .IR fd_out . | |
52 | It does not consume the data that is duplicated from | |
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53 | .IR fd_in ; |
54 | therefore, that data can be copied by a subsequent | |
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55 | .BR splice (2). |
56 | ||
57 | .I flags | |
58 | is a series of modifier flags, which share the name space with | |
59 | .BR splice (2) | |
60 | and | |
61 | .BR vmsplice (2): | |
62 | .TP 1.9i | |
63 | .B SPLICE_F_MOVE | |
c13182ef | 64 | Currently has no effect for |
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65 | .BR tee (); |
66 | see | |
67 | .BR splice (2). | |
68 | .TP | |
69 | .B SPLICE_F_NONBLOCK | |
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70 | Do not block on I/O; see |
71 | .BR splice (2) | |
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72 | for further details. |
73 | .TP | |
74 | .B SPLICE_F_MORE | |
c13182ef | 75 | Currently has no effect for |
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76 | .BR tee (), |
77 | but may be implemented in the future; see | |
78 | .BR splice (2). | |
79 | .TP | |
80 | .B SPLICE_F_GIFT | |
81 | Unused for | |
82 | .BR tee (); | |
83 | see | |
84 | .BR vmsplice (2). | |
85 | .SH RETURN VALUE | |
86 | Upon successful completion, | |
87 | .BR tee () | |
88 | returns the number of bytes that were duplicated between the input | |
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89 | and output. |
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 | |
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93 | .IR fd_in . |
94 | ||
c13182ef | 95 | On error, |
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96 | .BR tee () |
97 | returns \-1 and | |
98 | .I errno | |
99 | is set to indicate the error. | |
100 | .SH ERRORS | |
c13182ef | 101 | .TP |
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102 | .B EINVAL |
103 | .I fd_in | |
104 | or | |
105 | .I fd_out | |
106 | does not refer to a pipe; or | |
107 | .I fd_in | |
108 | and | |
109 | .I fd_out | |
110 | refer to the same pipe. | |
111 | .TP | |
112 | .B ENOMEM | |
113 | Out of memory. | |
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114 | .SH VERSIONS |
115 | The | |
2777b1ca | 116 | .BR tee () |
ceaeac24 | 117 | system call first appeared in Linux 2.6.17. |
2dd578fd | 118 | .SH "CONFORMING TO" |
8382f16d | 119 | This system call is Linux-specific. |
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120 | .SH NOTES |
121 | Conceptually, | |
122 | .BR tee () | |
123 | copies the data between the two pipes. | |
124 | In reality no real data copying takes place though: | |
125 | under the covers, | |
126 | .BR tee () | |
c13182ef | 127 | assigns data in the output by merely grabbing |
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128 | a reference to the input. |
129 | .SH EXAMPLE | |
130 | The following example implements a basic | |
131 | .BR tee (1) | |
132 | program using the | |
2777b1ca | 133 | .BR tee () |
c13182ef | 134 | system call. |
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135 | .nf |
136 | ||
137 | #define _GNU_SOURCE | |
138 | #include <fcntl.h> | |
139 | #include <stdio.h> | |
140 | #include <stdlib.h> | |
141 | #include <unistd.h> | |
142 | #include <assert.h> | |
143 | #include <errno.h> | |
144 | #include <limits.h> | |
145 | ||
146 | int | |
147 | main(int argc, char *argv[]) | |
148 | { | |
149 | int fd; | |
150 | int len, slen; | |
151 | ||
152 | assert(argc == 2); | |
153 | ||
154 | fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644); | |
29059a65 | 155 | if (fd == \-1) { |
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156 | perror("open"); |
157 | exit(EXIT_FAILURE); | |
158 | } | |
159 | ||
160 | do { | |
161 | /* | |
162 | * tee stdin to stdout. | |
163 | */ | |
164 | len = tee(STDIN_FILENO, STDOUT_FILENO, | |
165 | INT_MAX, SPLICE_F_NONBLOCK); | |
166 | ||
167 | if (len < 0) { | |
168 | if (errno == EAGAIN) | |
169 | continue; | |
170 | perror("tee"); | |
171 | exit(EXIT_FAILURE); | |
172 | } else | |
173 | if (len == 0) | |
174 | break; | |
175 | ||
176 | /* | |
177 | * Consume stdin by splicing it to a file. | |
178 | */ | |
179 | while (len > 0) { | |
180 | slen = splice(STDIN_FILENO, NULL, fd, NULL, | |
181 | len, SPLICE_F_MOVE); | |
182 | if (slen < 0) { | |
183 | perror("splice"); | |
184 | break; | |
185 | } | |
29059a65 | 186 | len \-= slen; |
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187 | } |
188 | } while (1); | |
189 | ||
190 | close(fd); | |
191 | exit(EXIT_SUCCESS); | |
192 | } | |
193 | .fi | |
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194 | .SH SEE ALSO |
195 | .BR splice (2), | |
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196 | .BR vmsplice (2), |
197 | .BR feature_test_macros (7) |