I was wondering if there's a way to wait for a file to be updated, and then read from it once it's updated. So if I have file.txt
, 开发者_StackOverflowI want to wait until something new is written to it, and then read it/process it/etc. Currently I am polling using Time::HiRes::sleep(.01)
, but I'm wondering if there's a better way. Thanks.
Yes there is a better way. On windows you can use the FileSystemWatcher interface, on Linux, use inotify.
Windows
use Win32::FileSystem::Watcher;
my $watcher = Win32::FileSystem::Watcher->new( "c:\\" );
# or
my $watcher = Win32::FileSystem::Watcher->new(
"c:\\",
notify_filter => FILE_NOTIFY_ALL,
watch_sub_tree => 1,
);
$watcher->start();
print "Monitoring started.";
sleep(5);
# Get a list of changes since start().
my @entries = $watcher->get_results();
# Get a list of changes since the last get_results()
@entries = $watcher->get_results();
# ... repeat as needed ...
$watcher->stop(); # or undef $watcher
foreach my $entry (@entries) {
print $entry->action_name . " " . $entry->file_name . "\n";
}
# Restart monitoring
# $watcher->start();
# ...
# $watcher->stop();
LINUX
use Linux::Inotify2;
my $inotify = new Linux::Inotify2();
foreach (@ARGV)
{
$inotify->watch($_, IN_ALL_EVENTS);
}
while (1)
{
# By default this will block until something is read
my @events = $inotify->read();
if (scalar(@events)==0)
{
print "read error: $!";
last;
}
foreach (@events)
{
printf "File: %s; Mask: %d\n", $_->fullname, $_->mask;
}
}
File::Tail will poll the file, but has a few advantages over your approach:
- The poll time is recomputed dynamically based on the number of lines written since the last poll
- If the file remains unchanged, polling will slow to avoid using up CPU
- File::Tail will detect if the file has been truncated, moved and/or recreated, and silently re-open the file for you
- It can tie a regular file handle which you can use like normal without any special API or syntax.
Example from the perldoc:
use File::Tail;
my $ref=tie *FH,"File::Tail",(name=>$name);
while (<FH>) {
print "$_";
}
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