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28 .\" @(#)pipe.2 8.1 (Berkeley) 6/4/93
36 .Nd create descriptor pair for interprocess communication
42 .Fn pipe "int fildes[2]"
44 .Fn pipe2 "int fildes[2]" "int flags"
51 which is an object allowing
52 bidirectional data flow,
53 and allocates a pair of file descriptors.
57 system call allows control over the attributes of the file descriptors
63 are constructed by a bitwise-inclusive OR of flags from the following
66 .Bl -tag -width ".Dv O_NONBLOCK"
68 Set the close-on-exec flag for the new file descriptors.
70 Set the non-blocking flag for the ends of the pipe.
75 argument is 0, the behavior is identical to a call to
78 By convention, the first descriptor is normally used as the
81 and the second is normally the
83 so that data written to
85 appears on (i.e., can be read from)
87 This allows the output of one program to be
90 the source's standard output is set up to be
91 the write end of the pipe,
92 and the sink's standard input is set up to be
93 the read end of the pipe.
94 The pipe itself persists until all its associated descriptors are
97 A pipe that has had an end closed is considered
99 Writing on such a pipe causes the writing process to receive
103 Widowing a pipe is the only way to deliver end-of-file to a reader:
104 after the reader consumes any buffered data, reading a widowed pipe
105 returns a zero count.
107 The bidirectional nature of this implementation of pipes is not
108 portable to older systems, so it is recommended to use the convention
109 for using the endpoints in the traditional manner when using a
110 pipe in one direction.
111 .Sh IMPLEMENTATION NOTES
117 As a result, system call traces such as those captured by
130 system calls will fail if:
134 argument points to an invalid memory location.
136 Too many descriptors are active.
138 The system file table is full.
140 Not enough kernel memory to establish a pipe.
145 system call will also fail if:
164 Bidirectional pipes were first used on
174 function became a wrapper around