bash script get result from test into variable

Question

I'm trying to learn Bash scripting and for fun I would like to write a script which will monitor the httpd.service.

The basic construct looks like this:

#!/bin/bash
SERVICE=httpd.service

if [ "systemctl show -p ActiveState $SERVICE | sed 's/ActiveState=//g'" != "active" ] && [ "systemctl show -p SubState $SERVICE | sed 's/SubState=//g'"  != "running" ]
then
        echo "$SERVICE is inactive" | mailx -r [email protected] -s "$SERVICE not running on $HOSTNAME"  [email protected]
fi

it works. Whether is written in a secure and best practice way, I guess not but its my second day and I first need to get an idea behind scripting in generall.

How can I get the result of the two testconditions in a variable so that I could print the status and substatus in to the mail ? I guess I could do something like:

#!/bin/bash

SERVICE=httpd.service

STATE=$(systemctl show -p ActiveState $SERVICE | sed 's/ActiveState=//g')
SUBSTATE=$(systemctl show -p SubState $SERVICE | sed 's/SubState=//g')

if [ "$STATE" != "active" ] && [ "SUBSTATE" != "running" ]
then
        echo "$SERVICE state is $STATE and substate is $SUBSTATE"
fi

But not sure if this is a elegant way to do this ?

EDIT

Thanks for all your valuable comments! I've up voted all of them!

So, basically I ended up doing it in the following way:

#!/bin/bash

SERVICE=httpd.service
HOST=$(grep '^ServerName' /etc/httpd/conf/httpd.conf | sed 's/^.* //')
[email protected]




if [ "$(systemctl show -p ActiveState $SERVICE | sed 's/ActiveState=//g')" = "active" ]
then
        echo "$SERVICE is running" >/dev/null
else
        systemctl restart $SERVICE 2>/dev/null
        if [ "$(systemctl show -p ActiveState $SERVICE | sed 's/ActiveState=//g')" = "active" ]
        then
                echo "$SERVICE on $HOST has been started" | mailx -r "${HOST}"@blabla.com -s "$SERVICE on $HOST restarted" $EMAIL
        else
                echo "$SERVICE on $HOST is stopped and could not be started!" | mailx -r "${HOST}"@blabla.com -s "$SERVICE on $HOST has encountered a problem!" $EMAIL
        fi
fi

Could you please have a look at it? Are there any style, not POSIX compliant things used ?

Answer 1

Your first script doesn't work, you need

if [ "$(cmd)" != "active" ]

instead of

if [ "cmd" != "active" ]

---

The second script looks good.
Take care about negated conditions combined with &&. It might not give the result your looking for. I think you want || instead of &&.

You don't need the g option to sed substitution here, but it doesn't hurt either.

---

But it would be more elegant if you'd use the systemctl integrated functions:

systemctl is-enabled httpd.service >/dev/null || echo "Service not enabled"
systemctl is-active httpd.service >/dev/null || echo "Service not active"
systemctl is-failed httpd.service >/dev/null && echo "Service is failed"

Answer 2

As @RoVo says, be careful with your logic. You probably want

if [[ ! ("$STATE" = "active" && "SUBSTATE" = "running") ]]

note the use of bash's [[ ... ]]

or more portably

case "$STATE,$SUBSTATE" in
    "active,running") echo ok ;;
                   *) echo not ok ;;
esac