1. Technology
Send to a Friend via Email
Linux / Unix Command: write
Command Library

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 to the file referenced by the file descriptor fd from the buffer starting at buf. POSIX requires that a read() 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 are returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately. If count is zero and the file descriptor refers to a regular file, 0 will be returned without causing any other effect. For a special file, the results are not portable.  

ERRORS

EBADF
fd is not a valid file descriptor or is not open for writing.
EINVAL
fd is attached to an object which is unsuitable for writing.
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' file size limit, or to write at a position past than the maximum allowed offset.
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.)
EAGAIN
Non-blocking I/O has been selected using O_NONBLOCK and the write would block.
EINTR
The call was interrupted by a signal before any data was written.
ENOSPC
The device containing the file referred to by fd has no room for the data.
EIO
A low-level I/O error occurred while modifying the inode.

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

CONFORMING TO

SVr4, SVID, POSIX, X/OPEN, 4.3BSD. SVr4 documents additional error conditions EDEADLK, ENOLCK, ENOLNK, ENOSR, ENXIO, or ERANGE. Under SVr4 a write may be interrupted and return EINTR at any point, not just before any data is written.  

SEE ALSO

close(2), fcntl(2), fsync(2), ioctl(2), lseek(2), open(2), read(2), select(2), fwrite(3), writev(3)


Important: Use the man command (% man) to see how a command is used on your particular computer.

>> Linux/Unix Command Library

>> Shell Command Library

You can opt-out at any time. Please refer to our privacy policy for contact information.

Discuss in my forum

©2014 About.com. All rights reserved.