I want to capture packets using tcpdump over a certain period of time. However, if there are not packets captured in that time period I would like the program to exit. tcpdump does not allow you to specify a time period just packets based on time period. So if I receive 0 packets over a specific time period it should exit. The source code (a mod of an old sniffer program) is as follows: 
 
open (fileOUT,  ">> /results.out") or dienice ("Can't open file for wr
+iting");
close(fileOUT);
open (STDIN,"/usr/sbin/tcpdump -lnx -s 1024 dst port 80 |");
while (<>) {
   if (/^\S/) {
      last unless $LIMIT--;
      while ($packet=~/(GET|POST|WWW-Authenticate|Authorization).+/g) 
+ {
         open (fileOUT,  ">> /results.out") or dienice ("Can't open fi
+le for writing");
         flock(fileOUT, 2);
         seek(fileOUT, 0, 2);
         print fileOUT "$client -> $host\t$&\n";
         close(fileOUT);
      }
      undef $client; undef $host; undef $packet;
      ($client,$host) = /(\d+\.\d+\.\d+\.\d+).+ > (\d+\.\d+\.\d+\.\d+)
+/
      if /P \d+:\d+\((\d+)\)/ && $1 > 0;
   }
   next unless $client && $host;
   s/\s+//;
   s/([0-9a-f]{2})\s?/chr(hex($1))/eg;
   tr/\x1F-\x7E\r\n//cd;
   $packet .= $_;
}

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I've tried using gmtime but it still continues reading even when it reaches a set time. Should I make the tcpdump a thread and then kill that thread after a specific time? Any comments/suggestions would be great. Thanks.

2004-11-22 Edited by Arunbear: Changed title from 'tcpdump', as per Monastery guidelines

In reply to tcpdump: setting a conditional timeout by intranetman

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