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 ULTRIX
tell
lseek(2) System Calls Manual lseek(2)Name
lseek, tell - move read or write pointer
Syntax
#include <sys/types.h>
#include <unistd.h>
pos = lseek(d, offset, whence)
off_t pos;
int d, whence;
off_t offset;
pos = tell(d)
off_t pos;
int d;
Description
The system call moves the file pointer associated with a file or device open for reading or writing.
The descriptor d refers to a file or device open for reading or writing. The system call sets the file pointer of d as follows:
o If whence is SEEK_SET, the pointer is set to offset bytes.
o If whence is SEEK_CUR the pointer is set to its current location plus offset.
o If whence is SEEK_END, the pointer is set to the size of the file plus offset.
Seeking beyond the end of a file and then writing to the file creates a gap or hole that does not occupy physical space and reads as zeros.
The system call returns the offset of the current byte relative to the beginning of the file associated with the file descriptor.
Environment
System Five
If you compile a program in the System Five environment, an invalid whence argument causes SIGSYS to be sent. This complies with the
behavior described in the System V Interface Definition (SVID), Issue 1.
Return Values
Upon successful completion, a long integer (the current file pointer value) is returned. This pointer is measured in bytes from the begin-
ning of the file, where the first byte is byte 0. (Note that some devices are incapable of seeking. The value of the pointer associated
with such a device is undefined.) If a value of -1 is returned, errno is set to indicate the error.
Diagnostics
The system call fails and the file pointer remains unchanged under the following conditions:
[EBADF] The fildes is not an open file descriptor.
[EINVAL] The whence is not a proper value.
[ESPIPE] The fildes is associated with a pipe or a socket.
See Alsodup(2), open(2)lseek(2)