perl function sysseek

The sysseek function in Perl is used to position the file pointer for a filehandle to a specified position. It is a low-level function and can be used to seek to any position in the file.

Here is the syntax for sysseek function:

sysseek FILEHANDLE, POSITION, WHENCE;

• FILEHANDLE: This is the filehandle of the file for which the file pointer has to be set.
• POSITION: This is the position in the file where the file pointer has to be set.
• WHENCE: This is the reference point for the POSITION parameter. It can take one of the following values:
  - 0 - POSITION is specified relative to the beginning of the file.
  • 1 - POSITION is specified relative to the current position of the file pointer.
  • 2 - POSITION is specified relative to the end of the file.

Here's an example that demonstrates the usage of `sysseek` function:

# Open the file in read-write mode
open(my $fh, "+<", "example.txt") or die "Cannot open file: $!";

# Move the file pointer to the 10th byte from the beginning of the file
sysseek($fh, 10, 0) or die "sysseek failed: $!";

# Read the next 5 bytes from the file
my $data;
sysread($fh, $data, 5) or die "sysread failed: $!";
print "Read data: $data\n";

# Move the file pointer to the beginning of the file
sysseek($fh, 0, 0) or die "sysseek failed: $!";

# Write some data to the file
syswrite($fh, "Hello, world") or die "syswrite failed: $!";

# Close the file
close($fh);

In this example, we first open a file "example.txt" in read-write mode using the open function. Then, we use the sysseek function to move the file pointer to the 10th byte from the beginning of the file. We use the sysread function to read the next 5 bytes from the file and print the data. After that, we use sysseek function again to move the file pointer to the beginning of the file and then use syswrite function to write some data to the file. Finally, we close the file using the close function.