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30 .\" @(#)pipe.2 8.1 (Berkeley) 6/4/93
31 .\"
32 .Dd July 17, 1994
33 .Dt PIPE 2
34 .Os
35 .Sh NAME
36 .Nm pipe
37 .Nd create descriptor pair for interprocess communication
38 .Sh LIBRARY
39 .Lb libc
40 .Sh SYNOPSIS
41 .In unistd.h
42 .Ft int
43 .Fn pipe "int fildes[2]"
44 .Sh DESCRIPTION
45 The
46 .Fn pipe
47 function
48 creates a
49 .Em pipe ,
50 which is an object allowing
51 unidirectional data flow,
52 and allocates a pair of file descriptors.
53 The first descriptor connects to the
54 .Em read end
55 of the pipe,
56 and the second connects to the
57 .Em write end ,
58 so that data written to
59 .Fa fildes[1]
60 appears on (i.e., can be read from)
61 .Fa fildes[0] .
62 This allows the output of one program to be
63 sent
64 to another program:
65 the source's standard output is set up to be
66 the write end of the pipe,
67 and the sink's standard input is set up to be
68 the read end of the pipe.
69 The pipe itself persists until all its associated descriptors are
70 closed.
71 .Pp
72 A pipe whose read or write end has been closed is considered
73 .Em widowed .
74 Writing on such a pipe causes the writing process to receive
75 a
76 .Dv SIGPIPE
77 signal.
78 Widowing a pipe is the only way to deliver end-of-file to a reader:
79 after the reader consumes any buffered data, reading a widowed pipe
80 returns a zero count.
81 .Sh RETURN VALUES
82 On successful creation of the pipe, zero is returned.
83 Otherwise, a value of \-1 is returned and the variable
84 .Va errno
85 set to indicate the
86 error.
87 .Sh ERRORS
88 The
89 .Fn pipe
90 call will fail if:
91 .Bl -tag -width Er
92 .It Bq Er EMFILE
93 Too many descriptors are active.
94 .It Bq Er ENFILE
95 The system file table is full.
96 .It Bq Er EFAULT
97 The
98 .Fa fildes
99 buffer is in an invalid area of the process's address space.
100 The reliable detection of this error cannot be guaranteed; when not
101 detected, a signal may be delivered to the process, indicating an
102 address violation.
103 .El
104 .Sh SEE ALSO
105 .Xr sh 1 ,
106 .Xr fork 2 ,
107 .Xr read 2 ,
108 .Xr socketpair 2 ,
109 .Xr write 2
110 .Sh STANDARDS
111 The
112 .Fn pipe
113 function conforms to
114 .St -p1003.1-90 .
115 .Sh HISTORY
116 A
117 .Fn pipe
118 function call appeared in
119 .At v6 .