How to concatenate stdin and a string?

Question

How to I concatenate stdin to a string, like this?

echo \"input\" | COMMAND \"string\"

and get

inputstring

Answer 1

use cat - to read from stdin, and put it in $() to throw away the trailing newline

echo input | COMMAND "$(cat -)string"

However why don't you drop the pipe and grab the output of the left side in a command substitution:

COMMAND "$(echo input)string"