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Old 11-25-2016, 10:59 AM   #1
backslashV
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Question Question about awk


Hi,

I am printing the children of a process using this command:

Code:
ps -aef | grep 13783 | grep -v grep | grep -v ps | grep -v $0
and it shows the children correctly. (2 in my case)

The thing is that when I pipe it to awk to get the PIDs like this:

Code:
ps -aef | grep 13783 | grep -v grep | grep -v ps | grep -v $0 | awk '{print $2}'
I get 3 numbers. I don't know where that 3rd number is coming from.
 
Old 11-25-2016, 11:47 AM   #2
jpollard
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You might check that "grep 13783" looks for the string 13783 - and that may be a substring of another process id.

I did a "ps -aef | grep $$ | grep -v grep | grep -v ps" to see what this looked like - and got two processes, one mine (1245), and one from another user (11245).

You can prevent that by doing better pattern search: grep " $pid " as the spaces will reduce that issue. It doesn't prevent the resulting string from being in some other field though.

To do that would require more of the effort to be put into the awk script. Let it do the search for the parent pid ( third field), as well as being able to remove the cmd 'ps' from the selected list.

Last edited by jpollard; 11-25-2016 at 11:51 AM.
 
Old 11-25-2016, 11:53 AM   #3
backslashV
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if i just do:

Code:
ps-aef | grep 13783
I get:

Code:
cs11amb  13783 13324  0 08:44 pts/0    00:00:00 bash
cs11amb  13971 13783  0 08:44 pts/0    00:00:00 vim ff
cs11amb  14000 13783  0 08:44 pts/0    00:00:00 vim ss
cs11amb  19461 13783  7 09:49 pts/0    00:00:00 ps -aef
cs11amb  19463 13783  0 09:49 pts/0    00:00:00 grep 13783
when i grep out the extras, I only get

Code:
cs11amb  13971 13783  0 08:44 pts/0    00:00:00 vim ff
cs11amb  14000 13783  0 08:44 pts/0    00:00:00 vim ss
which are the correct children and what I want.

The problem is when I use awk, it prints:

Code:
13971
14000
21253
 
Old 11-25-2016, 12:02 PM   #4
Turbocapitalist
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Is that last PID that of the "awk" process itself?

Also, with "awk" there you don't need any of the "grep" processes at all.
 
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Old 11-25-2016, 12:06 PM   #5
backslashV
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Quote:
Originally Posted by Turbocapitalist View Post
Is that last PID that of the "awk" process itself?

Also, with "awk" there you don't need any of the "grep" processes at all.
I swear to god I tried to grep out awk before but it still showed up.
It is working now. Thank youuu.

Could you be more specific when you say I don't need any of the greps?
 
Old 11-25-2016, 12:13 PM   #6
backslashV
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In a script, I am trying to put the children in an array by saying:

Code:
for child in `ps -aef | grep $pid | grep -v grep | grep -v ps | grep -v $0 | grep -v awk | grep -v bash | awk '{print $2}'`; do
	arrayOfChildren+=("$child")
done
but echoing the array afterward
instead of the children PIDs as the array contents I get:

5
5

If I do
Code:
echo `ps -p ${#arrayOfChildren[0]}`
echo `ps -p ${#arrayOfChildren[1]}`
I get

PID TTY TIME CMD 5 ? 00:00:00 stopper/0
PID TTY TIME CMD 5 ? 00:00:00 stopper/0

Last edited by backslashV; 11-25-2016 at 01:21 PM.
 
Old 11-25-2016, 12:47 PM   #7
pan64
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why don't you try pgrep -P ?
 
Old 11-25-2016, 12:48 PM   #8
backslashV
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Quote:
why don't you try pgrep -P ?
I am not allowed.
 
Old 11-25-2016, 01:16 PM   #9
pan64
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You will not be able to list all the children "in one", because all the members of your chain (grep, awk, whatever) will be children and you need to exclude them, but actually there can be other grep/awk/whatever children which should be reported but will be ignored too. The best you can do is to save the output of the command ps and process the result afterward, or use a single awk which will exclude itself and print everything else.
ps -aef | awk -vmypid=$$ { look for $3 as parent pid and also look for aw }

why aren't you allowed to use pgrep?
 
Old 11-25-2016, 01:23 PM   #10
backslashV
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Quote:
Originally Posted by pan64 View Post
You will not be able to list all the children "in one", because all the members of your chain (grep, awk, whatever) will be children and you need to exclude them, but actually there can be other grep/awk/whatever children which should be reported but will be ignored too. The best you can do is to save the output of the command ps and process the result afterward, or use a single awk which will exclude itself and print everything else.
ps -aef | awk -vmypid=$$ { look for $3 as parent pid and also look for aw }

why aren't you allowed to use pgrep?
I want to store the result of ps in an array.

Code:
for child in `ps -aef | grep $pid | grep -v grep | grep -v ps | grep -v $0 | grep -v awk | grep -v bash | awk '{print $2}'`; do
       arrayOfChildren+=("$child")
done
echoing the contents with ps shows:

Code:
PID TTY TIME CMD 5 ? 00:00:00 stopper/0
PID TTY TIME CMD 5 ? 00:00:00 stopper/0
so basically the contents of the array are:
5
5

but before putting into the array I echo the output of
Code:
ps -aef | grep $pid | grep -v grep | grep -v ps | grep -v $0 | grep -v awk | grep -v bash | awk '{print $2}'
and i get the correct children PIDs like this:
13432 13324

I am not sure why I am not allowed to use that. I just asked and the TA said no.
 
Old 11-25-2016, 02:35 PM   #11
backslashV
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Solved

It appears that the problem was putting a # before the array name: ${#arrayOfChildren[0]}
removing that solved the problem.
Thanks everyone.
 
Old 11-25-2016, 02:54 PM   #12
grail
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Also, here is your possible all awk solution to feed your loop:
Code:
ps -aef | awk -vpid=$pid '$3 == pid && $NF != "-aef" && $NF !~ "pid"'
 
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