Open file and print new line that is appended

[gunghopatriot]

Need to open a file and if a new line is appended, then need to print it.

Opening the file is no problem, but how does one check if a new line has been recently appended to the log file?

 

[feherke]

Hi

Just read, then wait, then start again :

[b]open[/b] F,[green][i]"</input/file"[/i][/green];

[b]while[/b] (1) {
  [b]print[/b] $_ [b]while[/b] <F>;
  [b]sleep[/b] 1;
}

( Neither [tt]tail -f[/tt] has better solution : waits [tt]-s[/tt] ( [tt]--sleep-interval[/tt] ) seconds, then tries to read again. )


Feherke.
feherke.github.io

 

[stevexff]

From CPAN, File::Tail seems to do what you want. It even recomputes the sleep time dynamically (up to a maximum limit) based on how active the log file is, so it doesn't continually poll the file when nothing much is happening.

Steve

[small]"Every program can be reduced by one instruction, and every program has at least one bug. Therefore, any program can be reduced to one instruction which doesn't work." (Object:erlDesignPatterns)[/small]

 

[prex1]

You can use the -M switch to test the file modification time:

my $lasttime=0;
my $myinputfile="myinputfile.log";
while(1){
  if(-M $myinputfile<$lasttime){
    $lasttime=-M "myinputfile";
    open F,$myinputfile;
    print $_ while <F>;
    close F;
  }
  sleep 1;
}

It is not difficult to add the dynamically calculated sleep time.

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[feherke]

Hi

Sorry Franco, but I am afraid that is not really practical :

[tt]-M Script start time minus file modification time, in days.[/tt]

( man perlfunc | -X )

So better keep using the good old [tt]stat[/tt] function.

Regarding your code, reading the whole file after each modification not sounds too good. Also expecting a modification time less than the $lasttime sounds abit back to the future...

The OP not specified the used operating system, so hopefully this not applies, but as I know, on Windows the file time granularity is not really fine and not all changes will be detected promptly.


Feherke.
feherke.github.io