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Top Forums Shell Programming and Scripting awk question Post 302208263 by ynir on Monday 23rd of June 2008 12:23:10 PM
Old 06-23-2008
Hi "awk", Thanks and sorry for not clarifying enough.

The line is part of a running and working bash script on Linux.
PID is a local variable and the awk line is using its value to print the relevant line from ps.
I don't want to change the code (unless I have too), rather understand why it is used that way.

to simplify it, it is something like:
Code:
function foo()
{
   local MY_PID=""
   #...
   MY_PID=get_my_pid
   LINE=`ps auwx | awk -v "PID=${MY_PID}" '$2 == PID {print $LN}'`
   do_something "${MY_PID}"
}

So, I understand the -v is used to declare variable, since ${MY_PID} will not be resolved inside 'single quotes' - right?

I still don't understand what is the $LN for?
Could anyone clarify? Is it a mistake, that works the same way as print $XXX works ???

Thanks
 

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LEARN ABOUT OSX

dapptrace

dapptrace(1m)							   USER COMMANDS						     dapptrace(1m)

NAME

       dapptrace - trace user and library function usage. Uses DTrace.

SYNOPSIS

       dapptrace [-acdeFlhoU] [-u lib] { -p PID | command }

DESCRIPTION

       dapptrace prints details on user and library function calls. By default it traces user functions only, options can be used to trace library
       activity.

       Of particular interest is the elapsed times and on cpu times, which can identify both function calls that are slow to complete,	and  those
       which are consuming CPU cycles.

       Since this uses DTrace, only users with root privileges can run this command.

OPTIONS

       -a     print all details

       -b bufsize
	      dynamic variable buffer size. Increase this if you notice dynamic variable drop errors. The default is "4m" for 4 megabytes per CPU.

       -c     print function call counts

       -d     print relative timestamps, us

       -e     print elapsed times, us

       -F     print flow indentation

       -l     force printing of pid/lwpid per line

       -o     print on-cpu times, us

       -p PID examine this PID

       -u lib trace this library instead

       -U     trace all library and user functions

EXAMPLES

       run and examine the "df -h" command,
	      # dapptrace df -h

       examine PID 1871,
	      # dapptrace -p 1871

       print using flow indents,
	      # dapptrace -Fp 1871

       print elapsed and CPU times,
	      # dapptrace -eop 1871

FIELDS

       PID/LWPID
	      Process ID / Lightweight Process ID

       RELATIVE
	      relative timestamps to the start of the thread, us (microseconds)

       ELAPSD elapsed time for this system call, us

       CPU    on-cpu time for this system call, us

       CALL(args)
	      function call name, with some arguments in hexadecimal

DOCUMENTATION

       See the DTraceToolkit for further documentation under the Docs directory. The DTraceToolkit docs may include full worked examples with ver-
       bose descriptions explaining the output.

EXIT

       dapptrace will run forever until Ctrl-C is hit, or if a command was executed dapptrace will finish when the command ends.

AUTHOR

       Brendan Gregg [Sydney, Australia]

SEE ALSO

       dappprof(1M), dtrace(1M), apptrace(1)

version 1.10							   May 14, 2005 						     dapptrace(1m)
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