Unix command to concatenate (attach) two strings?

For concatenating two string we use cat command.

Ex:- cat str1 str2

echo $var1 $var2

cat $str1 $str2 is WRONG - cat command will need file names as input

var1=$var1$var2

echo $var1

you can concatenate two strings by using the echop command..echo -e -n str1; echo str2 | cat

Variable1="Open"

Variable2="Systems"

Variable3=$Variable1$Variable2

echo $Variable3

-- Output OpenSystems

There are two different ways to do the same.

1.
var1 = "first"
var2 = "second"
var3 = $var1$var2

The only problem with the above solution is you can not attach the general text at hte end or in between of the text to create new string as variable which is not present so it will give an error.

BEST SOLUTION IS:

2.
var1 = "first"
var2 = "second"
var3 = ${var1}$var2

This will also work. In addtion to this, if you want to add some general text, you can add.
ex. var3 = $var1${var2}thisistestadddition
the var3 will be firstsecondthisistestadddition