Is there a more simple way to add text to a variable
I have

var="blue"

echo $var
blue green

var=$(echo "${var} green")

var="${var} green"

in bash:

$ var+=" green"
$ echo $var
blue green

Note that the braces aren't needed either unless what you want to add to the variable could be interpreted by the shell to be part of the variable name.

var=blue
echo "$var"
var="$var green"
echo "$var"
var="${var}red"
echo "$var"

blue
blue green
blue greenred