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

hi

I've written this perl script and it works.
I have only one problem and don't know howto change it.
During sleep time it should show the message:

"pls wait, ntop will be started"

but after I get the "Status" this message should be disappear.
On the end I should see only the "Status", but now I still have this message in the browser. 
#!/usr/bin/perl -w

use CGI::Carp qw(fatalsToBrowser);
use CGI;
my $query = new CGI;

print $query->header;
print "<html>\n";
print "<head>\n";
print "<title>ntop startup script</title>\n";
print "<STYLE TYPE='text/css'>\n";
print "h3 { color: red }\n";
print "a { text-decoration: none; font: bold 14pt/16pt Ariel, serif }"
+;
print "a:hover { color: red } /* when mouse is over link */";
print "</style>\n";
print "</head>\n";
print "<body bgcolor='#c0c0d0'>\n";
print "<center>";
print "<p><br></p>";
print "<p><br></p>";

print "pls wait, ntop will be started\n";

system `/usr/local/www/cgi-bin/ntop/ntop.sh stop` or die "cannot stop 
+ntop: $!";
sleep(8);
$cc = `sudo /usr/local/www/cgi-bin/ntop/ntop.sh start` or die "cannot 
+start ntop: $!";
print "Status: ",$cc,"\n";

print "</center>";
print "</body>";
print "</html>";

exit($cc);

[download]
kind regards
cc

Replies are listed 'Best First'.
Re: show a message only during the sleep time
by davidrw (Prior) on Jul 24, 2005 at 13:00 UTC
    well, keeping in mind you can't "unsend" or "erase" stuff send out to the browser, there are a few options..
    • general tip: use strict; and use warnings;
    • Refer to this thread: CGI::Application timeout, especially the merlyn article
    • general tip for this case: make sure auto-flush is on.. do: $|=1; before you start printing.
    • You could put the "pls wait" message in a <div> tag and add javascript code via <body onLoad="..."> that uses css dom to hide the message div so that it appears to vanish.
    • (probably best.. this will be a very simplifed, specific case of merlyn's article) Store the $cc result somewhere (i like Cache::FileCache) and redirect (i think using javascript/onLoad will work) to a cgi (same file w/flag maybe) that will fetch the $cc from the cache and display it.
[reply]
[d/l]
[select]
      hi davidrw

      I tried your trick,
      but I still have "pls wait !" on the screen and will not vanish: 
      ...................................
print "<body bgcolor='#c0c0d0'>\n";
print "<center>";
print "<p><br></p>";
print "<p><br></p>";
    print "<div> pls wait ! </div>\n";
    print "<SCRIPT LANGUAGE = \"JavaScript\">\n";
    print "<!-- \n";
    print "<body onLoad="...">\n";
    print "// -->\n";
    print "</SCRIPT>\n";
...................................

      [download]
[reply]
[d/l]
        Well, you have write the "..." javascript -- the elipsis was just a place holder (and note that we want to add javascript code by using the <body onLoad=""> attribute, NOT embed the body tag inside script tags). Also, note the clunkiness of print statements for this.. (and this is pretty general advice) at the minimum, at least use here-docs, and also keep in mind a more robust solution like Template::Toolkit or HTML::Template. So, back to the problem at hand, this is what i was envisioning: 
        print <<EOF;
<html>
<head>
  <title>ntop startup script</title>
  <STYLE TYPE='text/css'>
    h3 { color: red }
    a { text-decoration: none; font: bold 14pt/16pt Ariel, serif }
    a:hover { color: red } /* when mouse is over link */
  </style>
  <script language="javascript">
    function hideWaitMsg(){
      var obj = getElementById('wait_msg_text');
      obj.visible = false;
    }
  </script>
</head>
<body bgcolor='#c0c0d0' onLoad="hideWaitMsg()">
  <center>
  <p><br></p>
  <p><br></p>

  <div id="wait_msg_text">pls wait, ntop will be started</div>
EOF

        [download]
        That's the basic setup .. note that i just guessed at the javascript code in the hideWaitMsg() function -- that part is left as an excercise for the reader.
[reply]
[d/l]
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Re: show a message only during the sleep time
by Joost (Canon) on Jul 24, 2005 at 12:57 UTC
    You can either put some kind of javascript in your output that removes the "pls wait" line, or you can use CSS to place the "status:" line on top of the other, obscuring the old message. You might need to disable output buffering ($|=1). Ofcourse, you could also have the page reload once a second until the code is done, but that requires a bit more coordination.

    On an unrelated note: why are you exit()ing with the STDOUT output of sudo as the status code? And you should probably use taint mode.

    "What should it profit a man, if he should win a flame war, yet lose his cool?"
[reply]
[d/l]
Re: show a message only during the sleep time
by kwaping (Priest) on Jul 24, 2005 at 14:47 UTC
    This is a little "outside the box", but how about this: redirect (>) your ntop.sh output to an HTML file, then use an HTTP Refresh to load that page after a given time?
[reply]
Re: show a message only during the sleep time
by NateTut (Deacon) on Jul 24, 2005 at 15:25 UTC
    I'm not sure this would work in a browser, but it might, put a \r before your status print statement. This is the "carrige return" character which should just return you to the beginning of the line. \n does a "carrige return" to go back to the beginning of the line as well as a "line feed" to go to the next line (at least in Windoze systems).

    This is a trick used in console applications to simulate a continuously updating "status line" without all the fancy schmancy GUI stuff.
[reply]
[d/l]
[select]
      can you pls give some more details, how it should work.

      greetings
      cc
[reply]
        It (just printing \r) won't work in the context of a browser .. It can, as the poster states, work in the context of a console application, but note that something from curses or console or term will probably be better/more robust (again, just for console apps -- not your browser-context issue).
[reply]
[d/l]

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