Why does the error not appear when there is space before and after "=" in the Bash script?

I wrote the variable name foo in the question.

In an environment where there were no errors, the variable name used the name basename as the command. The command not found error did not appear, and it seemed to be treated as a variable with a blank string after the substitute line.

I have posted an answer to close the question, although it contains information that was not included in the question.

I don't need any space when I replace it with bash.Run line by line, so if you write foo="bar", you execute the foot command, where = and "bar" are arguments.Without the foo command, the command not found error appears.
It looks like ls-la./.If ls is changed to sdfsdfsdf, sdfsdf-la. / Same, command not found error should appear.