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2bc4bb77 | 1 | .\" This manpage is Copyright (C) 2006 Jens Axboe |
c11b1abf | 2 | .\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> |
2bc4bb77 | 3 | .\" |
93015253 | 4 | .\" %%%LICENSE_START(VERBATIM) |
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5 | .\" Permission is granted to make and distribute verbatim copies of this |
6 | .\" manual provided the copyright notice and this permission notice are | |
7 | .\" preserved on all copies. | |
8 | .\" | |
9 | .\" Permission is granted to copy and distribute modified versions of this | |
10 | .\" manual under the conditions for verbatim copying, provided that the | |
11 | .\" entire resulting derived work is distributed under the terms of a | |
12 | .\" permission notice identical to this one. | |
c13182ef | 13 | .\" |
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14 | .\" Since the Linux kernel and libraries are constantly changing, this |
15 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
16 | .\" responsibility for errors or omissions, or for damages resulting from | |
17 | .\" the use of the information contained herein. The author(s) may not | |
18 | .\" have taken the same level of care in the production of this manual, | |
19 | .\" which is licensed free of charge, as they might when working | |
20 | .\" professionally. | |
c13182ef | 21 | .\" |
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22 | .\" Formatted or processed versions of this manual, if unaccompanied by |
23 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 24 | .\" %%%LICENSE_END |
2bc4bb77 | 25 | .\" |
0649afd4 | 26 | .TH TEE 2 2014-12-31 "Linux" "Linux Programmer's Manual" |
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27 | .SH NAME |
28 | tee \- duplicating pipe content | |
29 | .SH SYNOPSIS | |
30 | .nf | |
b80f966b | 31 | .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" |
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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 | .\" | |
c13182ef MK |
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 | |
3111b6a6 | 58 | is a bit mask that is composed by ORing together |
0bd79129 | 59 | zero or more of the following values: |
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60 | .TP 1.9i |
61 | .B SPLICE_F_MOVE | |
c13182ef | 62 | Currently has no effect for |
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63 | .BR tee (); |
64 | see | |
65 | .BR splice (2). | |
66 | .TP | |
67 | .B SPLICE_F_NONBLOCK | |
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68 | Do not block on I/O; see |
69 | .BR splice (2) | |
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70 | for further details. |
71 | .TP | |
72 | .B SPLICE_F_MORE | |
c13182ef | 73 | Currently has no effect for |
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74 | .BR tee (), |
75 | but may be implemented in the future; see | |
76 | .BR splice (2). | |
77 | .TP | |
78 | .B SPLICE_F_GIFT | |
79 | Unused for | |
80 | .BR tee (); | |
81 | see | |
82 | .BR vmsplice (2). | |
83 | .SH RETURN VALUE | |
84 | Upon successful completion, | |
85 | .BR tee () | |
86 | returns the number of bytes that were duplicated between the input | |
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87 | and output. |
88 | A return value of 0 means that there was no data to transfer, | |
89 | and it would not make sense to block, because there are no | |
90 | writers connected to the write end of the pipe referred to by | |
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91 | .IR fd_in . |
92 | ||
c13182ef | 93 | On error, |
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94 | .BR tee () |
95 | returns \-1 and | |
96 | .I errno | |
97 | is set to indicate the error. | |
98 | .SH ERRORS | |
c13182ef | 99 | .TP |
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100 | .B EAGAIN |
101 | .B SPLICE_F_NONBLOCK | |
102 | was specified in | |
103 | .IR flags , | |
104 | and the operation would block. | |
105 | .TP | |
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106 | .B EINVAL |
107 | .I fd_in | |
108 | or | |
109 | .I fd_out | |
110 | does not refer to a pipe; or | |
111 | .I fd_in | |
112 | and | |
113 | .I fd_out | |
114 | refer to the same pipe. | |
115 | .TP | |
116 | .B ENOMEM | |
117 | Out of memory. | |
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118 | .SH VERSIONS |
119 | The | |
2777b1ca | 120 | .BR tee () |
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121 | system call first appeared in Linux 2.6.17; |
122 | library support was added to glibc in version 2.5. | |
47297adb | 123 | .SH CONFORMING TO |
8382f16d | 124 | This system call is Linux-specific. |
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125 | .SH NOTES |
126 | Conceptually, | |
127 | .BR tee () | |
128 | copies the data between the two pipes. | |
129 | In reality no real data copying takes place though: | |
130 | under the covers, | |
131 | .BR tee () | |
5dec7b73 | 132 | assigns data to the output by merely grabbing |
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133 | a reference to the input. |
134 | .SH EXAMPLE | |
f7d11fda | 135 | The example below implements a basic |
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136 | .BR tee (1) |
137 | program using the | |
2777b1ca | 138 | .BR tee () |
c13182ef | 139 | system call. |
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140 | Here is an example of its use: |
141 | ||
142 | .in +4n | |
143 | .nf | |
144 | $ \fBdate |./a.out out.log | cat\fP | |
145 | Tue Oct 28 10:06:00 CET 2014 | |
146 | $ \fBcat out.log\fP | |
147 | Tue Oct 28 10:06:00 CET 2014 | |
148 | .fi | |
149 | .in | |
150 | .SS Program source | |
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151 | .nf |
152 | ||
153 | #define _GNU_SOURCE | |
154 | #include <fcntl.h> | |
155 | #include <stdio.h> | |
156 | #include <stdlib.h> | |
157 | #include <unistd.h> | |
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158 | #include <errno.h> |
159 | #include <limits.h> | |
160 | ||
161 | int | |
162 | main(int argc, char *argv[]) | |
163 | { | |
164 | int fd; | |
165 | int len, slen; | |
166 | ||
6b34fb3f | 167 | if (argc != 2) { |
99c1a999 SL |
168 | fprintf(stderr, "Usage: %s <file>\\n", argv[0]); |
169 | exit(EXIT_FAILURE); | |
6b34fb3f | 170 | } |
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171 | |
172 | fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644); | |
29059a65 | 173 | if (fd == \-1) { |
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174 | perror("open"); |
175 | exit(EXIT_FAILURE); | |
176 | } | |
177 | ||
178 | do { | |
179 | /* | |
180 | * tee stdin to stdout. | |
181 | */ | |
182 | len = tee(STDIN_FILENO, STDOUT_FILENO, | |
183 | INT_MAX, SPLICE_F_NONBLOCK); | |
184 | ||
185 | if (len < 0) { | |
186 | if (errno == EAGAIN) | |
187 | continue; | |
188 | perror("tee"); | |
189 | exit(EXIT_FAILURE); | |
190 | } else | |
191 | if (len == 0) | |
192 | break; | |
193 | ||
194 | /* | |
195 | * Consume stdin by splicing it to a file. | |
196 | */ | |
197 | while (len > 0) { | |
198 | slen = splice(STDIN_FILENO, NULL, fd, NULL, | |
199 | len, SPLICE_F_MOVE); | |
200 | if (slen < 0) { | |
201 | perror("splice"); | |
202 | break; | |
203 | } | |
29059a65 | 204 | len \-= slen; |
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205 | } |
206 | } while (1); | |
207 | ||
208 | close(fd); | |
209 | exit(EXIT_SUCCESS); | |
210 | } | |
211 | .fi | |
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212 | .SH SEE ALSO |
213 | .BR splice (2), | |
0a4f8b7b | 214 | .BR vmsplice (2) |