为什么这个PHP代码不能在Linux中使用双引号的命令行上运行

Question

I have access to an Ubuntu server with PHP 7.0. I can run the following code without any problems:

php -r "echo 'hello world';"

But when I add an assignment operator like this:

php -r "echo 'hello world'; $t = 'hello world';"

I get the following error:

PHP Parse error: syntax error, unexpected '=', expecting end of file in Command line code

I just realized while typing this question that this is probably happening because the shell is trying to evaluate $t. Is there anyway to make it not evaluate $t? The reason I ask is because the code will contain single quotes. I suppose the simple solution would be to change the single quotes in the code to double quotes but if there is a way to do it without altering the code, it might be useful to know.

Answer 1

1. you can use single quotes for php code, but then you can't use them inside php code.

2. escape all special shell characters in php code with \, ie:

   php -r "echo 'hello world'; \$t = 'hello world';"