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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
45 .sp
46 .ne 2
47 .na
48 \fB\fBO_NONBLOCK\fR\fR
49 .ad
50 .RS 12n
51 Both file descriptors will be placed in non-blocking mode. This corresponds
52 to the \fBO_NONBLOCK\fR flag to \fBfcntl\fR(2).
53 .RE
54
55 .sp
56 .ne 2
57 .na
58 \fB\fBO_CLOEXEC\fR\fR
59 .ad
60 .RS 12n
61 Both file descriptors will be opened with the FD_CLOEXEC flag set. Both file
62 descriptors will be closed prior to any future exec() calls.
63 .RE
64
65 .sp
66 .LP
67 A read from \fIfildes\fR[\fB0\fR] accesses the data written to
68 \fIfildes\fR[\fB1\fR] on a first-in-first-out (FIFO) basis and a read from
69 \fIfildes\fR[\fB1\fR] accesses the data written to \fIfildes\fR[\fB0\fR] also
70 on a \fBFIFO\fR basis.
71 .sp
72 .LP
73 Upon successful completion \fBpipe()\fR marks for update the \fBst_atime\fR,
74 \fBst_ctime\fR, and \fBst_mtime\fR fields of the pipe.
75 .SH RETURN VALUES
76 .sp
77 .LP
78 Upon successful completion, \fB0\fR is returned. Otherwise, \fB\(mi1\fR is
79 returned and \fBerrno\fR is set to indicate the error.
80 .SH ERRORS
81 .sp
82 .LP
83 The \fBpipe()\fR and \fBpipe2()\fR functions will fail if:
84 .sp
85 .ne 2
86 .na
87 \fB\fBEMFILE\fR\fR
88 .ad
89 .RS 10n
90 More than {\fBOPEN_MAX\fR} file descriptors are already in use by this process.
91 .RE
92
93 .sp
94 .ne 2
95 .na
96 \fB\fBENFILE\fR\fR
97 .ad
98 .RS 10n
99 The number of simultaneously open files in the system would exceed a
100 system-imposed limit.
101 .RE
102
103 .sp
104 .ne 2
105 .na
106 \fB\fBEFAULT\fR\fR
107 .ad
108 .RS 10n
109 The \fIfildes[2]\fR argument points to an illegal address.
110 .RE
111
112 .sp
113 .LP
114 The \fBpipe2()\fR function will also fail if:
115 .sp
116 .ne 2
117 .na
118 \fB\fBEINVAL\fR\fR
119 .ad
120 .RS 10n
121 The \fIflags\fR argument is illegal. Valid \fIflags\fR are zero or a
122 bitwise inclusive-OR of \fBO_CLOEXEC\fR and \fBO_NONBLOCK\fR.
123 .RE
124
125
126 .SH ATTRIBUTES
127 .sp
128 .LP
129 See \fBattributes\fR(5) for descriptions of the following attributes:
130 .sp
131
132 .sp
133 .TS
134 box;
135 c | c
136 l | l .
137 ATTRIBUTE TYPE ATTRIBUTE VALUE
138 _
139 Interface Stability Standard
140 _
141 MT-Level Async-Signal-Safe
142 .TE
143
144 .SH SEE ALSO
145 .sp
146 .LP
147 \fBsh\fR(1), \fBfcntl\fR(2), \fBfstat\fR(2), \fBgetmsg\fR(2), \fBpoll\fR(2),
148 \fBputmsg\fR(2), \fBread\fR(2), \fBwrite\fR(2), \fBopen\fR(2),
149 \fBattributes\fR(5), \fBstandards\fR(5), \fBstreamio\fR(7I)
150 .SH NOTES
151 .sp
152 .LP
153 Since a pipe is bi-directional, there are two separate flows of data.
154 Therefore, the size (\fBst_size\fR) returned by a call to \fBfstat\fR(2) with
155 argument \fIfildes\fR[\fB0\fR] or \fIfildes\fR[\fB1\fR] is the number of bytes
156 available for reading from \fIfildes\fR[\fB0\fR] or \fIfildes\fR[\fB1\fR]
157 respectively. Previously, the size (\fBst_size\fR) returned by a call to
158 \fBfstat()\fR with argument \fIfildes\fR[\fB1\fR] (the write-end) was the
159 number of bytes available for reading from \fIfildes\fR[\fB0\fR] (the
160 read-end).