[SOLVED] If Then Else using "grep"

JoseKreif · 07-07-2015, 01:54 PM

Is there a way to determine True or False with a Grep Return?

I build a small menu program to kill and restart a VNC Server. This will save us Devs some time.

I added a command that goes

Code:

finger | grep "(:1)"

, this returns the VNC user. If the VNC Server is off for ":1", It shouldn't show up.

Is there a way to make it so its

Code:

if ( finger | grep "(:1)" ) Then
echo "Please Wait for VNC Server to close"
else
echo "VNC Server is down and ready to be restarted."

rtmistler · 07-07-2015, 02:34 PM

Yes.

grep(1) offers exit status which you can use in your script to determine if the outcome was successful versus not.

When using the grep exit status I always recommend checking for success because that is a zero, whereas "not found" is non-zero, but also error is a different non-zero value. Instead check for an affirmative found and then have an else case if you need to do something for the "not found & error" cases.

You check a command's exit status using $? within a script.

I'd enable "set -xv" within your script to ensure that you're looking at what you expect. Finger doesn't show that it provides exit status at all, which makes sense since it is a "report" type of command. But just make sure you don't get bit using a combination or a piped command and end up not looking at the exit status you intend to look at.

jpollard · 07-07-2015, 02:51 PM

Just a side note: the ":1" isn't always true. It can be any number depending on the system... Each time a user logs in with concurrent users the GUI the number will be incremented (right now, I have a :2 display, my wife has the :0, :1 was mine, until I locked it up and manually killed it) and every ssh login that forwards windows can have other numbers (by default, starting with 10, but that is up to the configuration of sshd).

Habitual · 07-07-2015, 04:43 PM

Code:

SERVICE='firefox'
if /usr/bin/pgrep $SERVICE > /dev/null; then echo "$SERVICE is running..."; else echo "Write code here to here to make it run"; exit 1; fi

speweth:
firefox is running...

finger is not reliable as a service test. Better to test the {finger} port, (using nc, or telnet....)

JoseKreif · 07-08-2015, 08:57 AM

Quote:

Originally Posted by jpollard

Just a side note: the ":1" isn't always true. It can be any number depending on the system... Each time a user logs in with concurrent users the GUI the number will be incremented (right now, I have a :2 display, my wife has the :0, :1 was mine, until I locked it up and manually killed it) and every ssh login that forwards windows can have other numbers (by default, starting with 10, but that is up to the configuration of sshd).

In some causes yes, But I am from the IT Department, when we VNC into one of our locations, we are (:1), and that's the way we configured it. Now is I ssh, I would be (192.168.x.x), however (:1) will still show up on the finger list since that is the VNC server.

JoseKreif · 07-08-2015, 09:21 AM

All good now.

Code:

 
if finger | grep -q "(:1)"; then
  echo -e "\n VNC Server Is Not Fully Closed Yet, Try again in 5 seconds"
else
  echo -e "\n VNC Server has been killed. You may now start it back up"
fi ;;

http://oi58.tinypic.com/fmj2te.jpg

Not sure where my other reply went, but @jpollard, I know what you are saying, but I am from the IT Department (at Corporate) and the connection we use in VNC is "192.168.x.x:1". The VNC server confirguration is set to make a ":1" spot for us to log into. Only the IT department has that. So the Code I build kills and starts that ":1". It will remain ":1" for us all the time.

Now if we SSH into the server, and we will, because we need to in order to kill and restart it, we will be listed on finger as (192.168.x.x).

http://oi59.tinypic.com/2qmn23d.jpg