Sets FILEHANDLE's system position in bytes using lseek(2). FILEHANDLE may
be an expression whose value gives the name of the filehandle. The values
for WHENCE are
to set the new position to POSITION;
to set the it
to the current position plus POSITION; and
to set it to EOF plus
POSITION, typically negative.
Note the emphasis on bytes: even if the filehandle has been set to operate
on characters (for example using the
I/O layer), the
family of functions use byte offsets, not character offsets,
because seeking to a character offset would be very slow in a UTF-8 file.
For WHENCE, you may also use the constants
(start of the file, current position, end of the file)
from the Fcntl module. Use of the constants is also more portable
than relying on 0, 1, and 2. For example to define a "systell" function:
Returns the new position, or the undefined value on failure. A position
of zero is returned as the string
"0 but true"
true on success and false on failure, yet you can still easily determine
the new position.