I try to install mcrypt in my docker image based on `php:7.2-apache`. Therefore I use the RUN-Command from the documentation and also answerd [here](https://stackoverflow.com/questions/47181369/how-to-install-mcrypt-on-docker) but I receive this error:

```
error: /usr/src/php/ext/mcrypt does not exist

usage: /usr/local/bin/docker-php-ext-install [-jN] ext-name [ext-name ...]

   ie: /usr/local/bin/docker-php-ext-install gd mysqli
   /usr/local/bin/docker-php-ext-install pdo pdo_mysql
   /usr/local/bin/docker-php-ext-install -j5 gd mbstring mysqli pdo pdo_mysql shmop

if custom ./configure arguments are necessary, see docker-php-ext-configure

Possible values for ext-name:
bcmath bz2 calendar ctype curl dba dom enchant exif fileinfo filter ftp  gd gettext gmp hash iconv imap interbase intl json ldap mbstring mysqli oci8  odbc opcache pcntl pdo pdo_dblib pdo_firebird pdo_mysql pdo_oci pdo_odbc pdo_pgsql pdo_sqlite pgsql phar posix pspell readline recode reflection session shmop simplexml snmp soap sockets sodium spl standard sysvmsg sysvsem sysvshm tidy tokenizer wddx xml xmlreader xmlrpc xmlwriter xsl zend_test zip

Some of the above modules are already compiled into PHP; please check
the output of "php -i" to see which modules are already loaded.
ERROR: Service 'web' failed to build: The command '/bin/sh -c apt-get update && apt-get install -y          libfreetype6-dev          libjpeg62-turbo-dev          libmcrypt-dev          libpng-dev     && docker-php-ext-install -j$(nproc) iconv mcrypt gd mbstring zip' returned a non-zero code: 1

```

My Dockerfile:

```
FROM php:7.2-apache

RUN apt-get update && apt-get install -y \
     libfreetype6-dev \
     libjpeg62-turbo-dev \
     libmcrypt-dev \
     libpng-dev \
&& docker-php-ext-install -j$(nproc) iconv mcrypt gd mbstring zip
#    && docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ \
#    && docker-php-ext-install -j$(nproc) gd

COPY ./etc/000-default.conf /etc/apache2/sites-available/

EXPOSE 80

```

Has anybody an idea how to solve or how to get the needed files in the requested folder?

Thanks!