How to evaluate grep result in bash?

I want to grep a specific status of a service (tomcat8.service).

Only if the string was found, I want to execute some logic.

Problem: even if I execute the script on service name that does not exist ("asd" in this example), the if $status still matches and prints out. But why?

status = $(systemctl status asd.service | grep 'active')
echo $status
if $status
then echo "$SERVICE was active" exit 0
fi
exit 0

Result output is: asd.service was active, which is certainly not true.

The echo $status prints: status: Unknown job: =

2 Answers

You can make use of grep's return status.

systemctl status asd.service | grep 'active' \ && status=active \ || status=not_active
if [ "$status" == "active" ]; then [...]
fi

or even easier:

test $(systemctl status asd.service | grep 'active') \ && echo "$SERVICE was active"

or if you prefer if:

if $(systemctl status asd.service | grep 'active'); then echo "$SERVICE was active"
fi

Anyways, take care about the keywords inactive, not active, active (exited) or alike. This will also match your grep statement. See the comments. Thanks @ Terrance for the hint.

Update:

No need for grep. systemctl has the command is-active included.

systemctl -q is-active asd.service \ && echo "$SERVICE was active"

or:

if systemctl -q is-active asd.service; then echo "is active";
fi

Some code review comments:

• sh/bash/ksh/zsh variable assignments look like var=value -- no spaces around the = are allowed. (documentation)
• status=$(some command) -- the status variable hold the output of the command, not the exit status. The exit status is in the $? variable

• the if statement acts on the exit status of the subsequent command (documentation)

  if some_comment; then action1; else action2; fi

  Most often, the command is [ or [[ to test some condition.

  However, grep has a clear exit status: 0 if the pattern was found, 1 otherwise. So you want this:

  if systemctl status asd.service | grep -q 'active'; then echo "$SERVICE was active"
  fi