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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15 | .\" manual page may be incorrect or out-of-date.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 | .\" |
9ba01802 | 26 | .TH TEE 2 2019-03-06 "Linux" "Linux Programmer's Manual" |
2bc4bb77 MK |
27 | .SH NAME |
28 | tee \- duplicating pipe content | |
29 | .SH SYNOPSIS | |
30 | .nf | |
b80f966b | 31 | .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" |
2bc4bb77 | 32 | .B #include <fcntl.h> |
dbfe9c70 | 33 | .PP |
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 | |
2bc4bb77 | 55 | .BR splice (2). |
efeece04 | 56 | .PP |
2bc4bb77 | 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 | |
c13182ef MK |
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 | |
2bc4bb77 | 91 | .IR fd_in . |
efeece04 | 92 | .PP |
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 | |
5ca397fa SK |
103 | .IR flags |
104 | or one of the file descriptors had been marked as nonblocking | |
105 | .RB ( O_NONBLOCK ) , | |
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106 | and the operation would block. |
107 | .TP | |
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108 | .B EINVAL |
109 | .I fd_in | |
110 | or | |
111 | .I fd_out | |
112 | does not refer to a pipe; or | |
113 | .I fd_in | |
114 | and | |
115 | .I fd_out | |
116 | refer to the same pipe. | |
117 | .TP | |
118 | .B ENOMEM | |
119 | Out of memory. | |
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120 | .SH VERSIONS |
121 | The | |
2777b1ca | 122 | .BR tee () |
c95b6ae1 MK |
123 | system call first appeared in Linux 2.6.17; |
124 | library support was added to glibc in version 2.5. | |
47297adb | 125 | .SH CONFORMING TO |
8382f16d | 126 | This system call is Linux-specific. |
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127 | .SH NOTES |
128 | Conceptually, | |
129 | .BR tee () | |
130 | copies the data between the two pipes. | |
131 | In reality no real data copying takes place though: | |
132 | under the covers, | |
133 | .BR tee () | |
5dec7b73 | 134 | assigns data to the output by merely grabbing |
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135 | a reference to the input. |
136 | .SH EXAMPLE | |
f7d11fda | 137 | The example below implements a basic |
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138 | .BR tee (1) |
139 | program using the | |
2777b1ca | 140 | .BR tee () |
c13182ef | 141 | system call. |
f7d11fda | 142 | Here is an example of its use: |
efeece04 | 143 | .PP |
f7d11fda | 144 | .in +4n |
b8302363 | 145 | .EX |
f7d11fda MK |
146 | $ \fBdate |./a.out out.log | cat\fP |
147 | Tue Oct 28 10:06:00 CET 2014 | |
148 | $ \fBcat out.log\fP | |
149 | Tue Oct 28 10:06:00 CET 2014 | |
b8302363 | 150 | .EE |
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151 | .in |
152 | .SS Program source | |
c7885256 | 153 | \& |
e7d0bb47 | 154 | .EX |
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155 | #define _GNU_SOURCE |
156 | #include <fcntl.h> | |
157 | #include <stdio.h> | |
158 | #include <stdlib.h> | |
159 | #include <unistd.h> | |
2bc4bb77 MK |
160 | #include <errno.h> |
161 | #include <limits.h> | |
162 | ||
163 | int | |
164 | main(int argc, char *argv[]) | |
165 | { | |
166 | int fd; | |
167 | int len, slen; | |
168 | ||
6b34fb3f | 169 | if (argc != 2) { |
d1a71985 | 170 | fprintf(stderr, "Usage: %s <file>\en", argv[0]); |
99c1a999 | 171 | exit(EXIT_FAILURE); |
6b34fb3f | 172 | } |
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173 | |
174 | fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644); | |
29059a65 | 175 | if (fd == \-1) { |
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176 | perror("open"); |
177 | exit(EXIT_FAILURE); | |
178 | } | |
179 | ||
180 | do { | |
181 | /* | |
182 | * tee stdin to stdout. | |
183 | */ | |
184 | len = tee(STDIN_FILENO, STDOUT_FILENO, | |
185 | INT_MAX, SPLICE_F_NONBLOCK); | |
186 | ||
187 | if (len < 0) { | |
188 | if (errno == EAGAIN) | |
189 | continue; | |
190 | perror("tee"); | |
191 | exit(EXIT_FAILURE); | |
192 | } else | |
193 | if (len == 0) | |
194 | break; | |
195 | ||
196 | /* | |
197 | * Consume stdin by splicing it to a file. | |
198 | */ | |
199 | while (len > 0) { | |
200 | slen = splice(STDIN_FILENO, NULL, fd, NULL, | |
201 | len, SPLICE_F_MOVE); | |
202 | if (slen < 0) { | |
203 | perror("splice"); | |
204 | break; | |
205 | } | |
29059a65 | 206 | len \-= slen; |
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207 | } |
208 | } while (1); | |
209 | ||
210 | close(fd); | |
211 | exit(EXIT_SUCCESS); | |
212 | } | |
e7d0bb47 | 213 | .EE |
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214 | .SH SEE ALSO |
215 | .BR splice (2), | |
6c97eb40 MK |
216 | .BR vmsplice (2), |
217 | .BR pipe (7) |