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Top Forums UNIX for Dummies Questions & Answers Doing a capture while another command is executing? Post 302414602 by MrEddy on Tuesday 20th of April 2010 02:55:04 PM
Doing a capture while another command is executing?

Basically what i'm trying to do is execute an update command and at the same time have the system do a TCPdump to file for that update traffic.

So I would like to connect the two commands so that the tcpdump terminates automatically when the update finishes/fails/whatever.

Right now I have it to the point where it will ask me which interface to capture on and then it will execute the update and start doing a capture.

Code:
echo; netstat -i | awk '{print $1}' ; echo ; echo 'Interface to capture on?' ; read capture ; update & tcpdump -n -i $capture -w /tmp/capture.cap host xxx.xxx.xxx.xxx



---------- Post updated at 01:24 PM ---------- Previous update was at 12:49 PM ----------

I have made a little progress on this.. Is there any way I can execute a command in the background and then save that new process ID to a variable?

So I could execute a command, save the process ID ex 1000 to variable Y.

Then when i'm done with all my commands I could just issue kill $Y to end the process still running?

So I basically just revered it. I run the capture in the background. Execute the update then kill the capture process.

---------- Post updated at 01:55 PM ---------- Previous update was at 01:24 PM ----------

Ok so looks like $! returns the process ID of the command that I just executed in the background.

So I got it to work by having it start the capture, then execute the update, then when the update is finished I did kill $! and that takes care of it.

I swear half the time I post something online I wind up figuring out my own answer before too long.

Last edited by Yogesh Sawant; 04-21-2010 at 03:54 AM.. Reason: added code tags
 
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SCREENCAPTURE(1)					    BSD General Commands Manual 					  SCREENCAPTURE(1)

NAME
screencapture -- capture images from the screen and save them to a file or the clipboard SYNOPSIS
screencapture [-SWCTMPcimswxto] file DESCRIPTION
The screencapture utility is not very well documented to date. A list of options follows. -c Force screen capture to go to the clipboard. -C Capture the cursor as well as the screen. Only allowed in non-interactive modes. -i Capture screen interactively, by selection or window. The control key will cause the screen shot to go to the clipboard. The space key will toggle between mouse selection and window selection modes. The escape key will cancel the interactive screen shot. -m Only capture the main monitor, undefined if -i is set. -M Open the taken picture in a new Mail message. -o In window capture mode, do not capture the shadow of the window. -P Open the taken picture in a Preview window. -s Only allow mouse selection mode. -S In window capture mode, capture the screen instead of the window. -t <format> Image format to create, default is png (other options include pdf, jpg, tiff and other formats). -T <seconds> Take the picture after a delay of <seconds>, default is 5. -w Only allow window selection mode. -W Start interaction in window selection mode. -x Do not play sounds. -a Do not capture attached windows. -r Do not add screen dpi meta data to captured file. files where to save the screen capture, 1 file per screen BUGS
Better documentation is needed for this utility. SECURITY CONSIDERATIONS
To capture screen content while logged in via ssh, you must launch screencapture in the same mach bootstrap hierarchy as loginwindow: PID=pid of loginwindow sudo launchctl bsexec $PID screencapture [options] HISTORY
A screencapture utility first appeared in Mac OS X v10.2. Mac OS June 16, 2004 Mac OS

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