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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 | .\" |
5fbde956 | 4 | .\" SPDX-License-Identifier: Linux-man-pages-copyleft |
2bc4bb77 | 5 | .\" |
4c1c5274 | 6 | .TH tee 2 (date) "Linux man-pages (unreleased)" |
2bc4bb77 MK |
7 | .SH NAME |
8 | tee \- duplicating pipe content | |
62e4321c AC |
9 | .SH LIBRARY |
10 | Standard C library | |
8fc3b2cf | 11 | .RI ( libc ", " \-lc ) |
2bc4bb77 MK |
12 | .SH SYNOPSIS |
13 | .nf | |
b80f966b | 14 | .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" |
2bc4bb77 | 15 | .B #include <fcntl.h> |
c6d039a3 | 16 | .P |
52520fb5 | 17 | .BI "ssize_t tee(int " fd_in ", int " fd_out ", size_t " len \ |
2bc4bb77 MK |
18 | ", unsigned int " flags ); |
19 | .fi | |
52520fb5 | 20 | .\" Return type was long before glibc 2.7 |
2bc4bb77 MK |
21 | .SH DESCRIPTION |
22 | .\" Example programs http://brick.kernel.dk/snaps | |
23 | .\" | |
24 | .\" | |
c13182ef MK |
25 | .\" add a "tee(in, out1, out2)" system call that duplicates the pages |
26 | .\" (again, incrementing their reference count, not copying the data) from | |
2bc4bb77 MK |
27 | .\" one pipe to two other pipes. |
28 | .BR tee () | |
29 | duplicates up to | |
30 | .I len | |
31 | bytes of data from the pipe referred to by the file descriptor | |
32 | .I fd_in | |
33 | to the pipe referred to by the file descriptor | |
34 | .IR fd_out . | |
35 | It does not consume the data that is duplicated from | |
c13182ef MK |
36 | .IR fd_in ; |
37 | therefore, that data can be copied by a subsequent | |
2bc4bb77 | 38 | .BR splice (2). |
c6d039a3 | 39 | .P |
2bc4bb77 | 40 | .I flags |
3111b6a6 | 41 | is a bit mask that is composed by ORing together |
0bd79129 | 42 | zero or more of the following values: |
2bc4bb77 MK |
43 | .TP 1.9i |
44 | .B SPLICE_F_MOVE | |
c13182ef | 45 | Currently has no effect for |
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46 | .BR tee (); |
47 | see | |
48 | .BR splice (2). | |
49 | .TP | |
50 | .B SPLICE_F_NONBLOCK | |
c13182ef MK |
51 | Do not block on I/O; see |
52 | .BR splice (2) | |
2bc4bb77 MK |
53 | for further details. |
54 | .TP | |
55 | .B SPLICE_F_MORE | |
c13182ef | 56 | Currently has no effect for |
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57 | .BR tee (), |
58 | but may be implemented in the future; see | |
59 | .BR splice (2). | |
60 | .TP | |
61 | .B SPLICE_F_GIFT | |
62 | Unused for | |
63 | .BR tee (); | |
64 | see | |
65 | .BR vmsplice (2). | |
66 | .SH RETURN VALUE | |
67 | Upon successful completion, | |
68 | .BR tee () | |
69 | returns the number of bytes that were duplicated between the input | |
c13182ef MK |
70 | and output. |
71 | A return value of 0 means that there was no data to transfer, | |
72 | and it would not make sense to block, because there are no | |
73 | writers connected to the write end of the pipe referred to by | |
2bc4bb77 | 74 | .IR fd_in . |
c6d039a3 | 75 | .P |
c13182ef | 76 | On error, |
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77 | .BR tee () |
78 | returns \-1 and | |
79 | .I errno | |
80 | is set to indicate the error. | |
81 | .SH ERRORS | |
c13182ef | 82 | .TP |
b7224af9 MK |
83 | .B EAGAIN |
84 | .B SPLICE_F_NONBLOCK | |
85 | was specified in | |
1ae6b2c7 | 86 | .I flags |
5ca397fa SK |
87 | or one of the file descriptors had been marked as nonblocking |
88 | .RB ( O_NONBLOCK ) , | |
b7224af9 MK |
89 | and the operation would block. |
90 | .TP | |
2bc4bb77 MK |
91 | .B EINVAL |
92 | .I fd_in | |
93 | or | |
94 | .I fd_out | |
95 | does not refer to a pipe; or | |
96 | .I fd_in | |
97 | and | |
98 | .I fd_out | |
99 | refer to the same pipe. | |
100 | .TP | |
101 | .B ENOMEM | |
102 | Out of memory. | |
3113c7f3 | 103 | .SH STANDARDS |
4131356c AC |
104 | Linux. |
105 | .SH HISTORY | |
106 | Linux 2.6.17, | |
107 | glibc 2.5. | |
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108 | .SH NOTES |
109 | Conceptually, | |
110 | .BR tee () | |
111 | copies the data between the two pipes. | |
112 | In reality no real data copying takes place though: | |
113 | under the covers, | |
114 | .BR tee () | |
5dec7b73 | 115 | assigns data to the output by merely grabbing |
2bc4bb77 | 116 | a reference to the input. |
a14af333 | 117 | .SH EXAMPLES |
f7d11fda | 118 | The example below implements a basic |
2bc4bb77 MK |
119 | .BR tee (1) |
120 | program using the | |
2777b1ca | 121 | .BR tee () |
c13182ef | 122 | system call. |
f7d11fda | 123 | Here is an example of its use: |
c6d039a3 | 124 | .P |
f7d11fda | 125 | .in +4n |
b8302363 | 126 | .EX |
ba81327a | 127 | $ \fBdate | ./a.out out.log | cat\fP |
f7d11fda MK |
128 | Tue Oct 28 10:06:00 CET 2014 |
129 | $ \fBcat out.log\fP | |
130 | Tue Oct 28 10:06:00 CET 2014 | |
b8302363 | 131 | .EE |
f7d11fda MK |
132 | .in |
133 | .SS Program source | |
c7885256 | 134 | \& |
33857069 | 135 | .\" SRC BEGIN (tee.c) |
e7d0bb47 | 136 | .EX |
2bc4bb77 | 137 | #define _GNU_SOURCE |
4ae706b0 | 138 | #include <errno.h> |
2bc4bb77 | 139 | #include <fcntl.h> |
4ae706b0 | 140 | #include <limits.h> |
2bc4bb77 MK |
141 | #include <stdio.h> |
142 | #include <stdlib.h> | |
0320049e | 143 | #include <sys/types.h> |
2bc4bb77 | 144 | #include <unistd.h> |
fe5dba13 | 145 | \& |
2bc4bb77 MK |
146 | int |
147 | main(int argc, char *argv[]) | |
148 | { | |
0b94bd78 AC |
149 | int fd; |
150 | ssize_t len, slen; | |
fe5dba13 | 151 | \& |
6b34fb3f | 152 | if (argc != 2) { |
d1a71985 | 153 | fprintf(stderr, "Usage: %s <file>\en", argv[0]); |
99c1a999 | 154 | exit(EXIT_FAILURE); |
6b34fb3f | 155 | } |
fe5dba13 | 156 | \& |
2bc4bb77 | 157 | fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644); |
29059a65 | 158 | if (fd == \-1) { |
2bc4bb77 MK |
159 | perror("open"); |
160 | exit(EXIT_FAILURE); | |
161 | } | |
fe5dba13 | 162 | \& |
3be51e47 | 163 | for (;;) { |
2bc4bb77 MK |
164 | /* |
165 | * tee stdin to stdout. | |
166 | */ | |
167 | len = tee(STDIN_FILENO, STDOUT_FILENO, | |
168 | INT_MAX, SPLICE_F_NONBLOCK); | |
2bc4bb77 MK |
169 | if (len < 0) { |
170 | if (errno == EAGAIN) | |
171 | continue; | |
172 | perror("tee"); | |
173 | exit(EXIT_FAILURE); | |
4208f16e AC |
174 | } |
175 | if (len == 0) | |
176 | break; | |
fe5dba13 | 177 | \& |
2bc4bb77 MK |
178 | /* |
179 | * Consume stdin by splicing it to a file. | |
180 | */ | |
181 | while (len > 0) { | |
182 | slen = splice(STDIN_FILENO, NULL, fd, NULL, | |
183 | len, SPLICE_F_MOVE); | |
184 | if (slen < 0) { | |
185 | perror("splice"); | |
706ff40f | 186 | exit(EXIT_FAILURE); |
2bc4bb77 | 187 | } |
29059a65 | 188 | len \-= slen; |
2bc4bb77 | 189 | } |
3be51e47 | 190 | } |
fe5dba13 | 191 | \& |
2bc4bb77 MK |
192 | close(fd); |
193 | exit(EXIT_SUCCESS); | |
194 | } | |
e7d0bb47 | 195 | .EE |
33857069 | 196 | .\" SRC END |
2bc4bb77 MK |
197 | .SH SEE ALSO |
198 | .BR splice (2), | |
6c97eb40 MK |
199 | .BR vmsplice (2), |
200 | .BR pipe (7) |