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.
Program is as following
Program gives the output as zero, though the file 'example.txt' do exist with so data in it.
Thanks.
Last edited by jim mcnamara; 09-24-2012 at 02:43 PM..
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 OSF1
lseek
lseek(2) System Calls Manual lseek(2)NAME
lseek - Moves read-write file offset
SYNOPSIS
#include <sys/types.h> #include <unistd.h>
off_t lseek ( int filedes, off_t offset, int whence );
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
lseek(): XSH5.0, XNS5.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies a file descriptor obtained from a successful open() or fcntl() function. Specifies a value, in bytes, that is used in conjunc-
tion with the whence parameter to set the file pointer. A negative value causes seeking in the reverse direction. The resulting file posi-
tion may also be negative. Specifies how to interpret the offset parameter in setting the file pointer associated with the filedes parame-
ter. Values for the whence parameter are: Sets the file pointer to the value of the offset parameter. Sets the file pointer to its cur-
rent location plus the value of the offset parameter. Sets the file pointer to the size of the file plus the value of the offset parame-
ter.
DESCRIPTION
The lseek() function sets the file offset for the open file specified by the filedes parameter. The whence parameter determines how the
offset is to be interpreted.
The lseek() function allows the file offset to be set beyond the end of existing data in the file. If data is later written at this point,
subsequently reading data in the gap returns bytes with the value 0 (zero) until data is actually written into the gap.
By itself, the lseek() function does not extend the size of the file.
RETURN VALUES
Upon successful completion, the resulting pointer location (the file offset), measured in bytes from the beginning of the file, is
returned. If the lseek() function fails, the file offset remains unchanged, a value of (off_t) - 1 is returned, and errno is set to indi-
cate the error.
ERRORS
If the lseek() function fails, the file offset remains unchanged and errno may be set to one of the following values: The filedes parameter
is not an open file descriptor. The whence parameter is an invalid value or the resulting file offset would be invalid. The filedes
parameter is associated with a pipe (FIFO), a socket, or a multiplexed special file.
The filedes parameter underlying the stream is associated with a socket.
RELATED INFORMATION
Functions: fcntl(2), fseek(3), open(2), read(2), write(2)
Standards: standards(5) delim off
lseek(2)