seek - reposition file pointer for random-access I/O
seek FILEHANDLE,POSITION,WHENCE
Sets FILEHANDLE’s position, just like the fseek() call of stdio. FILEHANDLE may be an expression whose value gives the name of the filehandle. The values for WHENCE are 0 to set the new position to POSITION, 1 to set it to the current position plus POSITION, and 2 to set it to EOF plus POSITION (typically negative). For WHENCE you may use the constants SEEK_SET, SEEK_CUR, and SEEK_END from either the IO::Seekable or the POSIX module. Returns 1 upon success, 0 otherwise.
If you want to position file for sysread() or syswrite(), don’t use seek() -- buffering makes its effect on the file’s system position unpredictable and non-portable. Use sysseek() instead.
On some systems you have to do a seek whenever you switch between reading and writing. Amongst other things, this may have the effect of calling stdio’s clearerr(3). A WHENCE of 1 (SEEK_CUR) is useful for not moving the file position:
seek(TEST,0,1);
This is also useful for applications emulating tail -f. Once you hit EOF on your read, and then sleep for a while, you might have to stick in a seek() to reset things. The seek() doesn’t change the current position, but it does clear the end-of-file condition on the handle, so that the next <FILE> makes Perl try again to read something. We hope.
If that doesn’t work (some stdios are particularly cantankerous), 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);
}