Fixed systemctl command handling

[meetgandhi-dev]

Fixed systemctl command handling

I got following warning while installing zenoh-bridge-ros2dds

$ sudo apt-get install --reinstall zenoh-bridge-ros2dds 
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 8 not upgraded.
Need to get 5,468 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 https://download.eclipse.org/zenoh/debian-repo  zenoh-bridge-ros2dds 1.2.1 [5,468 kB]
Fetched 5,468 kB in 16s (333 kB/s)                                                                                                                                          
(Reading database ... 413532 files and directories currently installed.)
Preparing to unpack .../zenoh-bridge-ros2dds_1.2.1_amd64.deb ...
Unpacking zenoh-bridge-ros2dds (1.2.1) over (1.2.1) ...
Setting up zenoh-bridge-ros2dds (1.2.1) ...
WARNING: 'systemctl' not found - cannot install zenoh-bridge-ros2dds as a service.
/usr/bin/systemctl

I believe the handling of command output is not working on different bash. I tried to reproduce the issue using simple bash scripts:

test1.sh

#!/bin/sh
if ! command -v systemctl &> /dev/null
then
	echo "WARNING: 'systemctl' not found - cannot install zenoh-bridge-ros2dds as a service."
	exit 0
fi
echo "Found"

which produced following output:

$ ./test1.sh 
WARNING: 'systemctl' not found - cannot install zenoh-bridge-ros2dds as a service.
/usr/bin/systemctl

I believe the more proper way of using the command can be following:

test2.sh

#!/bin/sh
SYSTEMCTL_CMD=$(command -v systemctl)
if [ -z "$SYSTEMCTL_CMD" ]; then
	echo "systemctl command not be found"
	exit 0
fi
echo "Found $SYSTEMCTL_CMD"

which produces following output:

$ ./test2.sh 
Found /usr/bin/systemctl

This PR incorporates the same.
Note: Fixes #139

[github-actions]

PR missing one of the required labels: {'documentation', 'bug', 'new feature', 'dependencies', 'breaking-change', 'internal', 'enhancement'}