File::Tail on win32

perlAffen has asked for the wisdom of the Perl Monks concerning the following question:

I have been trying to use this module to do a tail -f on a windows logfile. I had some perl code to do it that I posted before and below, but it was reading the whole file and thus using too much memory. I tried ppm to load File::Tail and it looks for File::HiRes, yet the PM goes in Time::HiRes. I have struggled for hours trying to get this PM loaded.
I am ready to pay someone to help me.
I just need an efficient way to that won't use alot of memory to 'tail -f' a large windows file. That is all.

perl somescript.pl thefile > outputfile

I have this

$firstrun = 1;
while(1) {
    if ( -s $file ) {
    sleep 1;
open(TF,$file) || next ;
seek(TF,0,0);
@lines=<TF>;
my $curpos=tell(TF);
close(TF);
    if ( $firstrun < 1 ){
    foreach $lyne (@lines){
        printf $lyne;    
    }
    }
sleep 1;
$firstrun = 0;
while(-s $file ) {
  open(TF,$file) || last ;
  seek(TF,$curpos,0);
  @lines=<TF>;
  $curpos = tell(TF);
  last if ((stat(_))[7] < $curpos);
    foreach $lyne (@lines){
    printf $lyne;    
    }    
  close(TF);
  sleep 1;
}
}
else
    { sleep 5; }
}
[download]

but it is a memory hog. Plus, sometimes I am not allowed to install PMs like File::Tail.
I like this offered by another Monk, but I am not skilled enough (see above) to turn it into efficient code.

while (1) {
    stat the file
    if size of file changed since last time {
        open file
        seek to previous EOF
        print file contents until EOF
        save EOF position for next time
        close the file
    }

    sleep for x seconds
}
[download]

Can anyone help with making the above not read through the whole file, possibly becoming more memory efficient ?
Thanks

Comment on File::Tail on win32 Select or Download Code

Replies are listed 'Best First'.
Re: File::Tail on win32 by GrandFather (Saint) on Nov 29, 2005 at 23:20 UTC
THe following sample code should do it for you. You should omit the updateFile related code - that's just there to get the test file updated. `use strict; use warnings; my $logFileName = 'test.txt'; my $lastPos = 0; my $endTime = time + 60; while (time < $endTime) { next if ! -e $logFileName; next if $lastPos >= -s $logFileName; open inFile, '<', $logFileName; seek inFile, $lastPos, 0; print while <inFile>; $lastPos = tell inFile; close inFile; } continue { sleep (5); updateFile (); } sub updateFile { open outFile, '>>', $logFileName; print outFile 'Line added to file at ' . (join ', ', localtime) . "\n" +; close outFile; }` [download] Printed: Line added to file at 30, 16, 12, 30, 10, 105, 3, 333, 1 Line added to file at 35, 16, 12, 30, 10, 105, 3, 333, 1 Line added to file at 40, 16, 12, 30, 10, 105, 3, 333, 1 Line added to file at 45, 16, 12, 30, 10, 105, 3, 333, 1 Line added to file at 50, 16, 12, 30, 10, 105, 3, 333, 1 Line added to file at 55, 16, 12, 30, 10, 105, 3, 333, 1 Line added to file at 0, 17, 12, 30, 10, 105, 3, 333, 1 Line added to file at 5, 17, 12, 30, 10, 105, 3, 333, 1 Line added to file at 10, 17, 12, 30, 10, 105, 3, 333, 1 Line added to file at 15, 17, 12, 30, 10, 105, 3, 333, 1 Line added to file at 20, 17, 12, 30, 10, 105, 3, 333, 1 [download] DWIM is Perl's answer to Gödel	[reply] [d/l] [select]
Re^2: File::Tail on win32 by perlAffen (Sexton) on Nov 30, 2005 at 00:47 UTC
thanks, I'll hook it up to large file and try it.	[reply]
some more help by perlAffen (Sexton) on Nov 30, 2005 at 01:44 UTC
The script behaves strangely when the source file is removed and recreated. like so, test.txt is created by doing echo "" > test.txt run -> perl this.pl other window (ow) echo one >> test.txt one (ow) echo two >> test.txt two (ow) del /F test.txt (ow) echo uno > test.txt (ow) echo due >> test.txt (ow) echo tre >> test.txt re (ow) echo quattro >> test.txt quattro So it seems to hold on to the last cursor position and won't yield any output until that last postion is surpassed ? Also when you first run it, it outputs the entire file, is it possible to set $lastpos to its current EOF line ? ie Can it go to the bottom and wait for the next newline ? Also if I wanted to hand the output to a program, rather than print, how would I change print while <inFile>; ?? Thanks !	[reply]
Re: some more help by GrandFather (Saint) on Nov 30, 2005 at 03:26 UTC
This modified version may be closer to what you want: use strict; use warnings; my $logFileName = 'test.txt'; my $highWater = -1; # Signal first time through while (1) { next if ! -e $logFileName; if ($highWater >= -s $logFileName) { $highWater = -s $logFileName; # Reset high water mark next; } open inFile, '<', $logFileName; seek inFile, $highWater, 0; #my @lines; # Uncomment to collate lines while (<inFile>) { print $_; # Replace with alternate code to handle output. #push @lines, $_; #Uncomment to collate lines } $highWater = tell inFile; close inFile; # Use @lines as required here to deal with added lines in one hit. e +g.: #print @lines; #Uncomment to print collated lines } continue { sleep (5); } [download] DWIM is Perl's answer to Gödel	[reply] [d/l]


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