Concatenate in bash the output of two commands without newline character

I'll try to explain the solution with another simple example

We've to concatenate the output of the following command:
"pwd" and "ls"

echo "$(pwd)$(ls)";

Output: 2 concatenated strings

You can use tr:

{ echo "The quick"; echo "brown fox"; } | tr "\n" " "

OR using sed:

{ echo "The quick"; echo "brown fox"; } | sed ':a;N;s/\n/ /;ba'

OUTPUT:

The quick brown fox 

echo "$(A)" "$(B)"

should work assuming that neither A nor B output multiple lines.

$ echo "$(echo "The quick")" "$(echo "brown fox")"
The quick brown fox