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write

send a message to another user

write.1.man
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1. write.1.man

Manpage of WRITE

WRITE

Section: Linux Programmer's Manual (1)
Updated: 12 March 1995
Index Return to Main Contents

NAME

write - send a message to another user

SYNOPSIS

write user [ttyname]

DESCRIPTION

Write allows you to communicate with other users, by copying lines from your terminal to theirs.

When you run the write command, the user you are writing to gets a message of the form:

: Message from yourname@yourhost on yourtty at hh:mm ...

Any further lines you enter will be copied to the specified user's terminal. If the other user wants to reply, they must run write as well.

When you are done, type an end-of-file or interrupt character. The other user will see the message EOF indicating that the conversation is over.

You can prevent people (other than the super-user) from writing to you with the mesg(1) command. Some commands, for example nroff(1) and pr(1), may disallow writing automatically, so that your output isn't overwritten.

If the user you want to write to is logged in on more than one terminal, you can specify which terminal to write to by specifying the terminal name as the second operand to the write command. Alternatively, you can let write select one of the terminals - it will pick the one with the shortest idle time. This is so that if the user is logged in at work and also dialed up from home, the message will go to the right place.

The traditional protocol for writing to someone is that the string `-o', either at the end of a line or on a line by itself, means that it's the other person's turn to talk. The string `oo' means that the person believes the conversation to be over.

HISTORY

A write command appeared in Version 6 AT&T UNIX.

AVAILABILITY

The write command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

This document was created by man2html using the manual pages.
Time: 17:08:29 GMT, January 19, 2012

2. write.2.man

Manpage of WRITE

WRITE

Section: Linux Programmer's Manual (2)
Updated: 2010-08-29
Index Return to Main Contents

NAME

write - write to a file descriptor

SYNOPSIS

#include <unistd.h>

ssize_t write(int fd, const void *buf, size_t count);

DESCRIPTION

write() writes up to count bytes from the buffer pointed buf to the file referred to by the file descriptor fd.

The number of bytes written may be less than count if, for example, there is insufficient space on the underlying physical medium, or the RLIMIT_FSIZE resource limit is encountered (see setrlimit(2)), or the call was interrupted by a signal handler after having written less than count bytes. (See also pipe(7).)

For a seekable file (i.e., one to which lseek(2) may be applied, for example, a regular file) writing takes place at the current file offset, and the file offset is incremented by the number of bytes actually written. If the file was open(2)ed with O_APPEND, the file offset is first set to the end of the file before writing. The adjustment of the file offset and the write operation are performed as an atomic step.

POSIX requires that a read(2) which can be proved to occur after a write() has returned returns the new data. Note that not all file systems are POSIX conforming.

RETURN VALUE

On success, the number of bytes written is returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately.

If count is zero and fd refers to a regular file, then write() may return a failure status if one of the errors below is detected. If no errors are detected, 0 will be returned without causing any other effect. If count is zero and fd refers to a file other than a regular file, the results are not specified.

ERRORS

EAGAIN: The file descriptor fd refers to a file other than a socket and has been marked nonblocking (O_NONBLOCK), and the write would block.
EAGAIN or EWOULDBLOCK: The file descriptor fd refers to a socket and has been marked nonblocking (O_NONBLOCK), and the write would block. POSIX.1-2001 allows either error to be returned for this case, and does not require these constants to have the same value, so a portable application should check for both possibilities.
EBADF: fd is not a valid file descriptor or is not open for writing.
EDESTADDRREQ: fd refers to a datagram socket for which a peer address has not been set using connect(2).
EFAULT: buf is outside your accessible address space.
EFBIG: An attempt was made to write a file that exceeds the implementation-defined maximum file size or the process's file size limit, or to write at a position past the maximum allowed offset.
EINTR: The call was interrupted by a signal before any data was written; see signal(7).
EINVAL: fd is attached to an object which is unsuitable for writing; or the file was opened with the O_DIRECT flag, and either the address specified in buf, the value specified in count, or the current file offset is not suitably aligned.
EIO: A low-level I/O error occurred while modifying the inode.
ENOSPC: The device containing the file referred to by fd has no room for the data.
EPIPE: fd is connected to a pipe or socket whose reading end is closed. When this happens the writing process will also receive a SIGPIPE signal. (Thus, the write return value is seen only if the program catches, blocks or ignores this signal.)

Other errors may occur, depending on the object connected to fd.

CONFORMING TO

SVr4, 4.3BSD, POSIX.1-2001.

Under SVr4 a write may be interrupted and return EINTR at any point, not just before any data is written.

NOTES

A successful return from write() does not make any guarantee that data has been committed to disk. In fact, on some buggy implementations, it does not even guarantee that space has successfully been reserved for the data. The only way to be sure is to call fsync(2) after you are done writing all your data.

If a write() is interrupted by a signal handler before any bytes are written, then the call fails with the error EINTR; if it is interrupted after at least one byte has been written, the call succeeds, and returns the number of bytes written.

COLOPHON

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