varível
foo="Hello"
foo="${foo} World"
echo "${foo}"
> Hello World
C0W
foo="Hello"
foo="${foo} World"
echo "${foo}"
> Hello WorldContext | Expression | Result (value of c)
--------------------------------------+-----------------------+---------------------
Two variables | c=$a$b | helloworld
A variable and a literal | c=${a}_world | hello_world
A variable and a literal | c=$1world | oneworld
A variable and a literal | c=$a/world | hello/world
A variable, a literal, with a space | c=${a}" world" | hello world
A more complex expression | c="${a}_one|${b}_2" | hello_one|world_2
Using += operator (Bash 3.1 or later) | c=$a; c+=$b | helloworld
Append literal with += | c=$a; c+=" world" | hello world