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Closing a system process after file creation (was: One for the Wisest Monks)

by Anonymous Monk
on Jun 02, 2002 at 11:02 UTC ( #171007=perlquestion: print w/replies, xml ) Need Help??

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

I am using a one up counter from a file to make ID keys for a db file. I have found a way to dynamically create a .dat file using this one up counter so I can have a log seperate from the database that coincides. I do this with the following command:

system "cat > $num.bat"; #(creates 19.bat if the one up counter is at 19)

now the question....how can I add a command in this string that will not only create the new file but close it automatically so the process dies?

update by boo_radley : title change
  • Comment on Closing a system process after file creation (was: One for the Wisest Monks)

Replies are listed 'Best First'.
Re: One for the Wisest Monks
by Zaxo (Archbishop) on Jun 02, 2002 at 11:14 UTC

    Your system call is waiting for input from stdin. You could call 'touch' instead, but how about a pure perl solution?

    {
    my $fh;
    open $fh, '>', "/path/to/${num}.bat" or die $!;
}

    [download]
    You are likely to want a more economical representation of your counter, sooner or later. You should think about flock when you design it.

    After Compline,
    Zaxo

[reply]
[d/l]
      I've tried this..or a reasonable facimile...I'll try again when I go back to work...perhaps I was making a permissions oversight.

      This command will create a file called $(num).bat? in the directory listed in the path?

      Sure hope it works!! I'll let ya know tomorrow!

      Thanks!
[reply]
Re: One for the Wisest Monks
by Matts (Deacon) on Jun 02, 2002 at 12:03 UTC
    If you really want to use system commands and not straight perl, try: 
    system "touch $num.bat";

    [download]
    Has the advantage of not doing anything to the file (except changing it's timestamp) if it already exists.
[reply]
[d/l]
      system "touch $num.bat";

      [download]
      But that unnecessarily starts a separate process, and is subject to security issues regarding the contents of $num.

      Much safer and faster: 

      open DUMMY, ">>$num.bat";
close DUMMY;

      [download]

      -- Randal L. Schwartz, Perl hacker

[reply]
[d/l]
[select]
            system touch => "$num.bat";

        [download]
        doesn't suffer from security issues regarding the content of $num. As for "much faster", I'm not quite convinced. You're doing disk I/O here, and that's likely to be the bottleneck anyway.

        Abigail

[reply]
[d/l]
[select]
      I like it!
[reply]
        Have it implemented and it's working GREAT! Thanks again!

        TexasTess
        "Great Spirits Often Encounter Violent Opposition From Mediocre Minds" --Albert Einstein
[reply]
Re: One for the Wisest Monks
by TexasTess (Beadle) on Jun 02, 2002 at 11:25 UTC
    BTW didn't mean for this to be anonymous....forgot to log in
[reply]
      Just a hint: change the site scheme in your User settings - then it is immediately visible when you're logged in and when not. :-)
      ____________
      Makeshifts last the longest.
[reply]

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