I tried to use lseek system call to determine the number of bytes in a file. To do so, I used open system call with O_APPEND flag to open a file. As lseek returns the current offset so I called lseek for opened file with offset as zero and whence as SEEK_CUR. So I guess it must return the number of bytes as the file is ready to append and lseek seeks only 0 bytes. But result is showing 0 bytes. Please correct me if I have understood wrong.
Your entire line of reasoning depends on the open() syscall placing the file pointer at the end of the file. That is not a given.
I just started shell coding and I'm a bit confused on how 'mv' works can someone explain to me how it works and if i did this correctly. Thanks.
echo "Enter Name of the first file:"
read file1
#echo $file1
if ; then
echo "Sorry, file does not exist."
exit 1
... (16 Replies)
recently my project needs me to lseek a position over 4G size....
i found in linux or unix the parameters are all ulong 32 bits...the limit dooms the movement of a position over 4G
I was told that i should lseek64 to meet my need... but i have no idea where i can get the function neither by "man... (8 Replies)
Hi Gurus:
I am trying to understand the following line of code.I did enough of googling to understand but no luck.Please help me understand the follow chunk of code:
X=$0
MOD=${X%/*}/env.ksh
X is the current script from which I am trying to execute.
Say if X=test.ksh
$MOD is echoing :... (3 Replies)
I know there is lseek() function that will allow to write or read from certain position in the file. Is there similar function that will let do same but for array rather then file? (9 Replies)
Hi everybody,
i've been googling for ages now and gotten kinda desperate... The question, however, might be rather trivial for the experts: What is it exactly, i.e. physically, the POSIX function (for a file) "lseek" does? Does it trigger some kind of synchronization on disk? Is it just for the... (4 Replies)
I think both write at the end of the file ......
but is there a sharp difference between those 2 instruction .....
thank you
this is my 3rd question today forgive me :D (1 Reply)
Hi,
We are facing issues while backing up our 1205 GB filesystem on LTO5 Tape. During backup the "backup: The lseek call failed." messages were generated, I want to know why these messages were generating
AIX version is: 6100-08-00-0000
backup: The date of this level 0 backup is Mon Mar 11... (4 Replies)
The following code:
int fd;
if (fd = open("mem", O_RDONLY) == -1)
return 1;
if (lseek(fd, 0, SEEK_SET) == -1) {
char *buf = malloc(512);
buf = strerror(errno);
printf("%s\n", buf);
return 1;
}
always returns with "illegal seek"... (2 Replies)
Discussion started by: Sir_Tomasz
2 Replies
LEARN ABOUT NETBSD
lseek
LSEEK(2) BSD System Calls Manual LSEEK(2)NAME
lseek, seek -- reposition read/write file offset
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
off_t
lseek(int fildes, off_t offset, int whence);
DESCRIPTION
The lseek() function repositions the offset of the file descriptor fildes to the argument offset according to the directive whence. The
argument fildes must be an open file descriptor. lseek() repositions the file pointer fildes as follows:
If whence is SEEK_SET, the offset is set to offset bytes.
If whence is SEEK_CUR, the offset is set to its current location plus offset bytes.
If whence is SEEK_END, the offset is set to the size of the file plus offset bytes.
The lseek() function allows the file offset to be set beyond the end of the existing end-of-file of the file. If data is later written at
this point, subsequent reads of the data in the gap return bytes of zeros (until data is actually written into the gap).
Some devices are incapable of seeking. The value of the pointer associated with such a device is undefined.
RETURN VALUES
Upon successful completion, lseek() returns the resulting offset location as measured in bytes from the beginning of the file. Otherwise, a
value of -1 is returned and errno is set to indicate the error.
ERRORS
lseek() will fail and the file pointer will remain unchanged if:
[EBADF] fildes is not an open file descriptor.
[EINVAL] whence is not a proper value, or the resulting file offset would be invalid.
[ESPIPE] fildes is associated with a pipe, socket, or FIFO.
SEE ALSO dup(2), open(2)STANDARDS
The lseek() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').
HISTORY
A seek() function appeared in Version 2 AT&T UNIX, later renamed into lseek() for ``long seek'' due to a larger offset argument type.
BUGS
This document's use of whence is incorrect English, but is maintained for historical reasons.
BSD April 3, 2010 BSD