01-09-2020
Hello mrAibo,
You might get some joy from the output of the stat command. The file is Modified as it is created and Changed as the content is written, however this might not be safe for a polling process to be sure the file is complete.
What is the overall goal of the process you are looking to automate?
It might be safer to write a flag file when the real IO has completed, e.g. the file name might be abc123def456.output and this grows as the data is written/transferred. At the end of the writing process, just touch abc123def456.output.complete A reading process should look for files ending .complete and only then attempt to work with the real data file. Of course, there is then an extra file to tidy away and an extra IO, but the time taken should be negligible.
Does this better suit what you need, or have I missed the point?
Kind regards,
Robin
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WRITE(2) System Calls Manual WRITE(2)
NAME
write, writev - write output
SYNOPSIS
cc = write(d, buf, nbytes)
int cc, d;
char *buf;
unsigned short nbytes;
#include <sys/types.h>
#include <sys/uio.h>
cc = writev(d, iov, iovcnt)
int cc, d;
struct iovec *iov;
int iovcnt;
DESCRIPTION
Write attempts to write nbytes of data to the object referenced by the descriptor d from the buffer pointed to by buf. Writev performs the
same action, but gathers the output data from the iovcnt buffers specified by the members of the iov array: iov[0], iov[1], ...,
iov[iovcnt-1].
For writev, the iovec structure is defined as
struct iovec {
caddr_t iov_base;
u_short iov_len;
};
Each iovec entry specifies the base address and length of an area in memory from which data should be written. Writev will always write a
complete area before proceeding to the next.
On objects capable of seeking, the write starts at a position given by the pointer associated with d, see lseek(2). Upon return from
write, the pointer is incremented by the number of bytes actually written.
Objects that are not capable of seeking always write from the current position. The value of the pointer associated with such an object is
undefined.
If the real user is not the super-user, then write clears the set-user-id bit on a file. This prevents penetration of system security by a
user who "captures" a writable set-user-id file owned by the super-user.
When using non-blocking I/O on objects such as sockets that are subject to flow control, write and writev may write fewer bytes than
requested; the return value must be noted, and the remainder of the operation should be retried when possible.
RETURN VALUE
Upon successful completion the number of bytes actually written is returned. Otherwise a -1 is returned and the global variable errno is
set to indicate the error.
ERRORS
Write and writev will fail and the file pointer will remain unchanged if one or more of the following are true:
[EBADF] D is not a valid descriptor open for writing.
[EPIPE] An attempt is made to write to a pipe that is not open for reading by any process.
[EPIPE] An attempt is made to write to a socket of type SOCK_STREAM that is not connected to a peer socket.
[EFBIG] An attempt was made to write a file that exceeds the process's file size limit or the maximum file size.
[EFAULT] Part of iov or data to be written to the file points outside the process's allocated address space.
[EINVAL] The pointer associated with d was negative.
[ENOSPC] There is no free space remaining on the file system containing the file.
[EDQUOT] The user's quota of disk blocks on the file system containing the file has been exhausted.
[EIO] An I/O error occurred while reading from or writing to the file system.
[EWOULDBLOCK] The file was marked for non-blocking I/O, and no data could be written immediately.
In addition, writev may return one of the following errors:
[EINVAL] Iovcnt was less than or equal to 0, or greater than 16.
[EINVAL] The sum of the iov_len values in the iov array overflowed a short.
SEE ALSO
fcntl(2), lseek(2), open(2), pipe(2), select(2)
4th Berkeley Distribution August 1, 1987 WRITE(2)