Linux shell scripting: How to store output from terminal in integers (but only numbers)?

Question

I'm new to shell scripting and here is my problem:
I want to store PID's from output of airmon-ng check to some variables (for ex: $1, $2, $3) so that I can execute kill $1 $2 $3. here is sample output of airmon-ng check:

Found 3 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after
a short period of time, you may want to kill (some of) them!

  PID Name
  707 NetworkManager
  786 wpa_supplicant
  820 dhclient

I want to grab numbers 707, 786, 820.
I tried using set 'airmon-ng check' and then using for loop:

set `airmon-ng check`
n=$#
for (( i=0; i<=n; i++ ))
do
        echo $i
done

it outputs 1,2,3,...36 not words or numbers so I couldn't figure out how I should do it.

I think There will be a better way to do this but I can't figure it out. So any ways are accepted :) — Irakli
– Irakli, Commented Aug 10, 2016 at 15:07

score 1 · Accepted Answer · 2016-08-10 15:25:05Z

1

airmon-ng check | egrep -o '\b[0-9]+\b' | xargs kill

egrep is grep with extended regular expressions (like grep -E), -o says to extract only the matching parts, \b matches word boundaries so you don't get any numbers accidentally occuring in process names or something, [0-9]+ matches one or more decimal digit, xargs kill passes all the matches as arguments to the kill command.

Note that parsing output intended to be read by humans might not always be a good idea. Also, just killing all those processes doesn't sound too smart either, but proper usage of airocrack is beyond this question.

edited Aug 10, 2016 at 15:25

answered Aug 10, 2016 at 15:18

user3035850

Sign up to request clarification or add additional context in comments.

2 Comments

sjsam Over a year ago

Not sure if this captures just the pids. You need a tighter check

user3035850 Over a year ago

Yeah, but the approach isn't stable anyway. It's just one more issue on top of thousands of other ;).

Jack Glasshard · Accepted Answer · 2016-08-10 15:15:47Z

0

You can get list of the PIDs separated by spaces e.g. like this (everything from the 1st column after "PID"):

l=`airmon-ng check | awk 'BEGIN { p=0 } { if (p) { print $1" "; } if ($1=="PID") { p=1 } }' | tr '\n' ' '`

answered Aug 10, 2016 at 15:15

Jack Glasshard

785 bronze badges

1 Comment

Irakli Over a year ago

Didn't even thought of it, Awesome. Real big thanks :)

barefly · Accepted Answer · 2016-08-10 15:23:07Z

0

Why not use grep?

myvar=$(airmon-ng check | grep '[0-9]\{3,6\}')

This assumes a PID of 3 to 6 digits, and will grab anything from the airmon-ng output of a similar length. So this may not work as well if the output includes other strings with digits of a similar length.

answered Aug 10, 2016 at 15:23

barefly

3882 gold badges4 silver badges14 bronze badges

3 Comments

sjsam Over a year ago

Not sure if this will output just the pids. What if the o/p contains numbers other than pids?

barefly Over a year ago

@sjsam Unfortunately I am not as well-versed in regexp as I'd like to be and put something together that would fit the typical PID format.

sjsam Over a year ago

Hmm.. From the output we may assume that the pids appear at the beginning, you just need a bit of googling to do the rest.

sjsam · Accepted Answer · 2016-08-10 15:26:55Z

0

I would use awk for this and store the output in an array

pids=( $(airmon-ng check | awk '/^[[:blank:]]+[[:digit:]]+[[:blank:]]+/{print $1}') )
#'pids' is an array
kill "${pids[@]}" #killing all the processes thus found.

edited Aug 10, 2016 at 15:26

answered Aug 10, 2016 at 15:21

sjsam

22k6 gold badges63 silver badges114 bronze badges

2 Comments

Irakli Over a year ago

real nice approach thanks. Unfortunately my rating is so low that I Can't Upvote the answer :)

sjsam Over a year ago

@Ika : Not a problem pal, you enjoy the life :)

Collectives™ on Stack Overflow

Linux shell scripting: How to store output from terminal in integers (but only numbers)?

4 Answers 4

2 Comments

1 Comment

3 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

1 Comment

3 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related