The reason why the shell variable assignment cannot have a space

Typical examples:

A=date

Echo $a established

A =date

echo $a not set up

Actually, the reason is simple.

The principle of the shell in interpreting the command is that the first symbol tag can only be a program or a command, when there is a space, the first symbol is "a", of course, it does not set up

Without a space, the first tag is "a=date" and the shell is interpreted as a variable assignment directive, so it can be passed.

This principle can also be used to explain a lot of things.

The reason why the shell variable assignment cannot have a space