July 17, 1994 PIPE 2

### NAME

pipe - create descriptor pair for interprocess communication

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```int` pipe(```int fildes[2]`)

### DESCRIPTION

The pipe(``) function creates a pipe, which is an object allowing unidirectional data flow, and allocates a pair of file descriptors. The first descriptor connects to the read end of the pipe, and the second connects to the write end, so that data written to ```fildes[1]` appears on (i.e., can be read from) ```fildes[0]`. This allows the output of one program to be sent to another program: the source's standard output is set up to be the write end of the pipe, and the sink's standard input is set up to be the read end of the pipe. The pipe itself persists until all its associated descriptors are closed.

A pipe whose read or write end has been closed is considered widowed. Writing on such a pipe causes the writing process to receive a ```SIGPIPE` signal. Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed pipe returns a zero count.

### RETURN VALUES

On successful creation of the pipe, zero is returned. Otherwise, a value of -1 is returned and the variable errno set to indicate the error.

### ERRORS

The pipe(``) call will fail if:

[```EMFILE`]
  Too many descriptors are active.

[```ENFILE`]
  The system file table is full.

[```EFAULT`]
  The ```fildes` buffer is in an invalid area of the process's address space. The reliable detection of this error cannot be guaranteed; when not detected, a signal may be delivered to the process, indicating an address violation.

### SEE ALSO

sh(1), fork(2), read(2), socketpair(2), write(2)

### STANDARDS

The pipe(``) function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'') .

### HISTORY

A pipe(``) function call appeared in Version 6 `AT&T UNIX`.