seekFILEHANDLE,OFFSET,WHENCE
This function positions the file pointer for
FILEHANDLE
, just
like the
fseek
(3) call of standard I/O. The first position in a
file is at offset 0, not offset 1, and offsets refer to byte positions,
not line numbers. (In general, since line lengths vary, it's not
possible to access a particular line number without examining the whole
file up to that line number, unless all your lines are known to be of a
particular length, or you've built an index that translates line numbers
into byte offsets.)
FILEHANDLE
may be an expression
whose value gives the name of the filehandle or a reference to a filehandle
object. The function returns 1 upon success, 0 otherwise.
For handiness, the function can calculate offsets from various file
positions for you. The value of
WHENCE
specifies which file
position your
OFFSET
is relative to:
0
, the beginning of
the file;
1
, the current position in the file; or
2
, the
end of the file.
OFFSET
may be negative for a
WHENCE
of
1
or
2
.
One interesting use for this function is to allow you to follow growing files, like this:
for (;;) {
while (<LOG>) {
... # Process file.
}
sleep 15;
seek LOG,0,1; # Reset end-of-file error.
}
The final seek clears the end-of-file error without moving the pointer. If that doesn't work (depending on your C library's standard I/O implementation), then you may need something more like this:
for (;;) {
for ($curpos = tell FILE; $_ = <FILE>; $curpos = tell FILE) {
# search for some stuff and put it into files
}
sleep $for_a_while;
seek FILE, $curpos, 0;
}
Similar strategies could be used to remember the seek addresses of each line in an array.
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