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Grep starting from a specific position

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Top Forums Shell Programming and Scripting Grep starting from a specific position
# 1  
Old 07-08-2011
Grep starting from a specific position
Hello people,
I'm scratch my head to find a solution to my problem, I'm absolutely sure this is very simple!!! Smilie

I'm using the tcpdump to show on the screen in real time the UCP traffic:
Code:
tcpdump -l -i bond1 -s 1514 -nntttt -A src or dst 192.168.1.5 and port 10000 | egrep "/51/"

The output will be something like:
Code:
a..'....P.o....P..E.....01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........
a..'....P.....nP..fE....02/00248/O/51/001234567889/1234567890//1//7///////0907110916.........
a..'....P......P..CF....03/00244/O/51/001234567889/1234567890//1//7///////0907110916.........

Now, the first chars (coming from TCP stack) is always different, but have always the same lenght (24 chars).

Is there a way to remove that chars adding a filter directly to the primary command??
Like starting output from 25th char and show on the screen something like: ?
Code:
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........
02/00248/O/51/001234567889/1234567890//1//7///////0907110916.........
03/00244/O/51/001234567889/1234567890//1//7///////0907110916.........

And also, is it possible to have a CR between each lines, like:
Code:
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........

02/00248/O/51/001234567889/1234567890//1//7///////0907110916.........

03/00244/O/51/001234567889/1234567890//1//7///////0907110916.........

Thanks!
Last edited by Lord Spectre; 07-08-2011 at 04:39 AM..
# 2  
Old 07-08-2011
Code:
 
$ cut -c25- test
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........

Code:
 
$ cut -c25- test | nawk '{printf("%s\n\n",$0)}'
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........
 
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........
 
01/00246/O/51/001234567889/1234567890//1//7///////0907110916.........

This User Gave Thanks to itkamaraj For This Post:
Lord Spectre
# 3  
Old 07-08-2011
Thanks for fast reply itkamaraj,
I already know the simple command cut, but how can I implement it in the tcpdump command?

As already told, the output will be shown @ the screen in real time, so I need to "cut" the output in real time! Smilie

EDIT: Got it!
Code:
tcpdump -l -i bond1 -s 1514 -nntttt -A src or dst 192.168.1.5 and port 10000 | cut -c25- | grep "51/"

But I cannot show the CR between the output lines!
I tried the following without success (no output shown):
Code:
tcpdump -l -i bond1 -s 1514 -nntttt -A src or dst 192.168.1.5 and port 10000 | cut -c25- | grep "51/" | nawk '{printf("%s\n\n",$0)}'

or
Code:
tcpdump -l -i bond1 -s 1514 -nntttt -A src or dst 192.168.1.5 and  port 10000 | cut -c25- | nawk  '{printf("%s\n\n",$0)}' | grep "51/"

Last edited by Lord Spectre; 07-08-2011 at 04:56 AM..
# 4  
Old 07-08-2011
Can you replace grep (in post# 1) with the below sed and try
Code:
sed '/51/s/.\{24\}\(.*\)/\1\n/'

# 5  
Old 07-08-2011
Quote:
Originally Posted by michaelrozar17
Can you replace grep (in post# 1) with the below sed and try
Code:
sed '/51/s/.\{24\}\(.*\)/\1\n/'

Nope! This is what I seen on the screen:

Code:
2011-07-08 09:56:07.118713 IP 192.168.1.5.10000 > 192.168.1.5.5000: . ack 938 win 62907
E..( .@.{...
a.Z
a..'....Rl.....P.............
2011-07-08 09:56:12.769254 IP 192.168.1.5.5000 > 192.168.1.5.10000: P 938:1334(396) ack 960 win 63784
E...:.@.@...
a..
a.Z..'......Rl.P..(1E...50/00394/O/53/192.168.1.55000/1234565/////////////2234234324/0/000/080711100001/3//E/////////////EF.
2011-07-08 09:56:12.836946 IP 192.168.1.5.10000 > 192.168.1.5.5000: P 960:982(22) ack 1334 win 64240
E..>!.@.{..L
a.Z
a..'....Rl.... P....(...50/00020/R/53/A///9B.
2011-07-08 09:56:12.876289 IP 192.168.1.5.5000 >192.168.1.5.10000: . ack 982 win 63784
E..(:.@.@..~

# 6  
Old 07-08-2011
Ok. Maybe there is difference in output you got and posted or there is different version of sed/machine.
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