Re^2: Autoflush fails

Thanks for your reply. What I want is to flush the results of "sudo /usr/sbin/tcpdump -i $Interface host $Multicast 2>/dev/null |" to TCPDump. I tried "$| = 1" but it didn't work either. Any suggestion I can make the while loop to print the traffic at once? I tried the sudo command in a bash shell and I can see the results right away. However, the output of the sudo tcpdump feeding to TCPDump is batched in my Perl program. This causes the rest of the codes(removed here) to fail.

Comment on Re^2: Autoflush fails

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Re^3: Autoflush fails by Anonymous Monk on May 31, 2012 at 04:09 UTC
Autoflush is something you do in your program, to control the output of your program , not something you can do to other programs Other than changing your invocation (sudo ... ) there is nothing you can do You say sudo ... works from bash, but does `sudo ... \|perl -pe 1` work the same?	[reply] [d/l]
Re^4: Autoflush fails by sophate (Beadle) on May 31, 2012 at 04:23 UTC
Really appreciate your help :-) The results of "sudo tcpdump" are redirected to STDOUT right away. `,"sudo /usr/sbin/tcpdump -i eth3 host 226.1.109.109 2> +/dev/null"` [download] However, the results are buffered if I pipe it to "perl -pe 1" `,"sudo /usr/sbin/tcpdump -i eth3 host 226.1.109.109 2> +/dev/null \| perl -pe 1"` [download] Any alternative to a file handle to get the sudo resluts from a pipe?	[reply] [d/l] [select]
Re^5: Autoflush fails by Anonymous Monk on May 31, 2012 at 05:31 UTC
However, the results are buffered if I pipe it to "perl -pe 1" You'll find they're probably buffered if you pipe to anything ( even cat ) So the solution is to ddg://tcpdump buffered and find tcpdump: Re: pipeline buffering which says if you don't specify -w, -U means "flush the standard output after the information for each packet is printed" So there you have it, install sufficiently modern version of tcpdump that comes with -U option that flushes more often FYI there also exists pcapdump, Net::Pcap::Easy... Tutorials: Network Programming: Perl and Net::Pcap	[reply]