How to print message in terminal with concat two strings in flutter?

It is more of a dart question. You can achieve that using:

print('Something $string1 something more ${someObject.string2} even more $string3'); 

In dart there are many string options.

For concatenation, you can do :

• 'hello $myVariable'
• "hello ${myVariable.myProperty}"
• 'hello ' 'world' (only works with string literals)
• 'hello' + myVariable

So in your case, you can do a print(" $str1 $str2")

Use $var instead of ${var} here