Question: I have tried to execute simple php code in the php interpreter.
When I executed the command `php -a` I getting the message

> 
> Interactive mode enabled
> 
> 
> 

Without any place for php input.
But I can execute a php code through the command `php -r`.
for example:

`php -r "echo 'Hello stackoverflow!';"`

> 
> Hello stackoverflow!
> 
> 
>

Answer: 
Install this:

```
php5-readline

```

then try use:

```
php -a

```
There seems to be a compilation / linkage error between your PHP and libreadline. This is documented in [PHP Bug #48759](https://bugs.php.net/bug.php?id=48759).

* Did you compile PHP by yourself? Did you play around with --configure and didn't do a proper `make clean` before your final build?
* Does `php -m` list readline as enabled feature? (Is PHP built with option `--with-readline`)
* What is you php version?
* What distribution do you use?
* Do you have the libreadline (the \*-dev package) installed?