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13 .TH PIPE 2 "Apr 19, 2013"
14 .SH NAME
15 pipe \- create an interprocess channel
16 .SH SYNOPSIS
17 .LP
18 .nf
19 #include <unistd.h>
20
21 \fBint\fR \fBpipe\fR(\fBint\fR \fIfildes\fR[2]);
22
23 \fBint\fR \fBpipe2\fR(\fBint\fR \fIfildes\fR[2], \fBint\fR \fIflags\fR);
24 .fi
25
26 .SH DESCRIPTION
27 .sp
28 .LP
29 The \fBpipe()\fR and pipe2() functions create an I/O mechanism called a
30 pipe and returns two file descriptors, \fIfildes\fR[\fB0\fR] and
31 \fIfildes\fR[\fB1\fR]. The files associated with \fIfildes\fR[\fB0\fR]
32 and \fIfildes\fR[\fB1\fR] are streams and are both opened for reading and
33 writing. The \fBpipe()\fR call will clear the \fBO_NDELAY\fR,
34 \fBO_NONBLOCK\fR, and \fBFD_CLOEXEC\fR flags on both file descriptors. The
35 \fBfcntl\fR(2) function can be used to set these flags.
36 .sp
37 .LP
38 The \fBpipe2()\fR call will clear the \fBO_NDELAY\fR on both filedescriptors.
39 The \fIflags\fR argument may be used to specify attributes on both file
40 descriptors. \fBpipe2()\fR called with a \fIflags\fR value of 0 will
41 behave identically to \fBpipe()\fR. Values for \fIflags\fR are constructed
42 by a bitwise-inclusive-OR of flags from the following list, defined in
43 <\fBfcntl.h\fR>.
44 .RE
45
46 .sp
47 .ne 2
48 .na
49 \fB\fBO_NONBLOCK\fR\fR
50 .ad
51 .RS 12n
52 Both file descriptors will be placed in non-blocking mode. This corresponds
53 to the \fBO_NONBLOCK\fR flag to \fBfcntl\fR(2).
54 .RE
55
56 .sp
57 .ne 2
58 .na
59 \fB\fBO_CLOEXEC\fR\fR
60 .ad
61 .RS 12n
62 Both file descriptors will be opened with the FD_CLOEXEC flag set. Both file
63 descriptors will be closed prior to any future exec() calls.
64 .RE
65
66 .sp
67 .LP
68 A read from \fIfildes\fR[\fB0\fR] accesses the data written to
69 \fIfildes\fR[\fB1\fR] on a first-in-first-out (FIFO) basis and a read from
70 \fIfildes\fR[\fB1\fR] accesses the data written to \fIfildes\fR[\fB0\fR] also
71 on a \fBFIFO\fR basis.
72 .sp
73 .LP
74 Upon successful completion \fBpipe()\fR marks for update the \fBst_atime\fR,
75 \fBst_ctime\fR, and \fBst_mtime\fR fields of the pipe.
76 .SH RETURN VALUES
77 .sp
78 .LP
79 Upon successful completion, \fB0\fR is returned. Otherwise, \fB\(mi1\fR is
80 returned and \fBerrno\fR is set to indicate the error.
81 .SH ERRORS
82 .sp
83 .LP
84 The \fBpipe()\fR and \fBpipe2()\fR functions will fail if:
85 .sp
86 .ne 2
87 .na
88 \fB\fBEMFILE\fR\fR
89 .ad
90 .RS 10n
91 More than {\fBOPEN_MAX\fR} file descriptors are already in use by this process.
92 .RE
93
94 .sp
95 .ne 2
96 .na
97 \fB\fBENFILE\fR\fR
98 .ad
99 .RS 10n
100 The number of simultaneously open files in the system would exceed a
101 system-imposed limit.
102 .RE
103
104 .sp
105 .ne 2
106 .na
107 \fB\fBEFAULT\fR\fR
108 .ad
109 .RS 10n
110 The \fIfildes[2]\fR argument points to an illegal address.
111 .RE
112
113 .sp
114 .LP
115 The \fBpipe2()\fR function will also fail if:
116 .sp
117 .ne 2
118 .na
119 \fB\fBEINVAL\fR\fR
120 .ad
121 .RS 10n
122 The \fIflags\fR argument is illegal. Valid \fIflags\fR are zero or a
123 bitwise inclusive-OR of \fBO_CLOEXEC\fR and \fBO_NONBLOCK\fR.
124 .RE
125
126
127 .SH ATTRIBUTES
128 .sp
129 .LP
130 See \fBattributes\fR(5) for descriptions of the following attributes:
131 .sp
132
133 .sp
134 .TS
135 box;
136 c | c
137 l | l .
138 ATTRIBUTE TYPE ATTRIBUTE VALUE
139 _
140 Interface Stability Standard
141 _
142 MT-Level Async-Signal-Safe
143 .TE
144
145 .SH SEE ALSO
146 .sp
147 .LP
148 \fBsh\fR(1), \fBfcntl\fR(2), \fBfstat\fR(2), \fBgetmsg\fR(2), \fBpoll\fR(2),
149 \fBputmsg\fR(2), \fBread\fR(2), \fBwrite\fR(2), \fBopen\fR(2),
150 \fBattributes\fR(5), \fBstandards\fR(5), \fBstreamio\fR(7I)
151 .SH NOTES
152 .sp
153 .LP
154 Since a pipe is bi-directional, there are two separate flows of data.
155 Therefore, the size (\fBst_size\fR) returned by a call to \fBfstat\fR(2) with
156 argument \fIfildes\fR[\fB0\fR] or \fIfildes\fR[\fB1\fR] is the number of bytes
157 available for reading from \fIfildes\fR[\fB0\fR] or \fIfildes\fR[\fB1\fR]
158 respectively. Previously, the size (\fBst_size\fR) returned by a call to
159 \fBfstat()\fR with argument \fIfildes\fR[\fB1\fR] (the write-end) was the
160 number of bytes available for reading from \fIfildes\fR[\fB0\fR] (the
161 read-end).