谁告诉你环境变量可以用于传输配置文件了…
可以用环境变量的意思是，有些软件既能识别环境变量中提供的配置，又能识别文件形式的配置，不过，很不幸，Nginx不在此列。

以wget为例，当设定HTTP代理时，可以选用以下任一方式：

• 在配置文件中加一行http_proxy = http://example.com/xxx

• 将系统环境变量$http_proxy设定为http://example.com/xxx

两种方法的作用是相同的。

当然，你可以在Docker容器里写一个Shell脚本，根据环境变量来修改配置文件的内容，但这就是另一个话题了。Github上有不少实现类似功能的工具，如Tiller。

补充一个资料：How Should I Get Application Configuration into my Docker Containers?

哦，在启动容器的时候要带参数，比如：
./docker run --detach --name wordpress --net wordnet --publish 80:80 --env WORDPRESS_DB_HOST=mysql --env WORDPRESS_DB_PASSWORD=xxxxxxxx wordpress:4.4

当然在容器启动命令里要处理带进来的参数：

cat /entrypoint.sh

#!/bin/bash
set -e

if [[ "$1" == apache2* ]] || [ "$1" == php-fpm ]; then
    if [ -n "$MYSQL_PORT_3306_TCP" ]; then
        if [ -z "$WORDPRESS_DB_HOST" ]; then
            WORDPRESS_DB_HOST='mysql'
        else
            echo >&2 'warning: both WORDPRESS_DB_HOST and MYSQL_PORT_3306_TCP found'
            echo >&2 "  Connecting to WORDPRESS_DB_HOST ($WORDPRESS_DB_HOST)"
            echo >&2 '  instead of the linked mysql container'
        fi
    fi

    if [ -z "$WORDPRESS_DB_HOST" ]; then
        echo >&2 'error: missing WORDPRESS_DB_HOST and MYSQL_PORT_3306_TCP environment variables'
        echo >&2 '  Did you forget to --link some_mysql_container:mysql or set an external db'
        echo >&2 '  with -e WORDPRESS_DB_HOST=hostname:port?'
        exit 1
    fi

    # if we're linked to MySQL and thus have credentials already, let's use them
    : ${WORDPRESS_DB_USER:=${MYSQL_ENV_MYSQL_USER:-root}}
    if [ "$WORDPRESS_DB_USER" = 'root' ]; then
        : ${WORDPRESS_DB_PASSWORD:=$MYSQL_ENV_MYSQL_ROOT_PASSWORD}
    fi
    : ${WORDPRESS_DB_PASSWORD:=$MYSQL_ENV_MYSQL_PASSWORD}
    : ${WORDPRESS_DB_NAME:=${MYSQL_ENV_MYSQL_DATABASE:-wordpress}}

    if [ -z "$WORDPRESS_DB_PASSWORD" ]; then
        echo >&2 'error: missing required WORDPRESS_DB_PASSWORD environment variable'
        echo >&2 '  Did you forget to -e WORDPRESS_DB_PASSWORD=... ?'
        echo >&2
        echo >&2 '  (Also of interest might be WORDPRESS_DB_USER and WORDPRESS_DB_NAME.)'
        exit 1
    fi

    if ! [ -e index.php -a -e wp-includes/version.php ]; then
        echo >&2 "WordPress not found in $(pwd) - copying now..."
        if [ "$(ls -A)" ]; then
            echo >&2 "WARNING: $(pwd) is not empty - press Ctrl+C now if this is an error!"
            ( set -x; ls -A; sleep 10 )
        fi
        tar cf - --one-file-system -C /usr/src/wordpress . | tar xf -
        echo >&2 "Complete! WordPress has been successfully copied to $(pwd)"
        if [ ! -e .htaccess ]; then
            # NOTE: The "Indexes" option is disabled in the php:apache base image
            cat > .htaccess <<-'EOF'
                # BEGIN WordPress
                <IfModule mod_rewrite.c>
                RewriteEngine On
                RewriteBase /
                RewriteRule ^index\.php$ - [L]
                RewriteCond %{REQUEST_FILENAME} !-f
                RewriteCond %{REQUEST_FILENAME} !-d
                RewriteRule . /index.php [L]
                </IfModule>
                # END WordPress
            EOF
            chown www-data:www-data .htaccess
        fi
    fi

    # TODO handle WordPress upgrades magically in the same way, but only if wp-includes/version.php's $wp_version is less than /usr/src/wordpress/wp-includes/version.php's $wp_version

    # version 4.4.1 decided to switch to windows line endings, that breaks our seds and awks
    # https://github.com/docker-library/wordpress/issues/116
    # https://github.com/WordPress/WordPress/commit/1acedc542fba2482bab88ec70d4bea4b997a92e4
    sed -ri 's/\r\n|\r/\n/g' wp-config*

    if [ ! -e wp-config.php ]; then
        awk '/^\/\*.*stop editing.*\*\/$/ && c == 0 { c = 1; system("cat") } { print }' wp-config-sample.php > wp-config.php <<'EOPHP'
// If we're behind a proxy server and using HTTPS, we need to alert Wordpress of that fact
// see also http://codex.wordpress.org/Administration_Over_SSL#Using_a_Reverse_Proxy
if (isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] === 'https') {
    $_SERVER['HTTPS'] = 'on';
}

EOPHP
        chown www-data:www-data wp-config.php
    fi

    # see http://stackoverflow.com/a/2705678/433558
    sed_escape_lhs() {
        echo "$@" | sed 's/[]\/$*.^|[]/\\&/g'
    }
    sed_escape_rhs() {
        echo "$@" | sed 's/[\/&]/\\&/g'
    }
    php_escape() {
        php -r 'var_export(('$2') $argv[1]);' "$1"
    }
    set_config() {
        key="$1"
        value="$2"
        var_type="${3:-string}"
        start="(['\"])$(sed_escape_lhs "$key")\2\s*,"
        end="\);"
        if [ "${key:0:1}" = '$' ]; then
            start="^(\s*)$(sed_escape_lhs "$key")\s*="
            end=";"
        fi
        sed -ri "s/($start\s*).*($end)$/\1$(sed_escape_rhs "$(php_escape "$value" "$var_type")")\3/" wp-config.php
    }

    set_config 'DB_HOST' "$WORDPRESS_DB_HOST"
    set_config 'DB_USER' "$WORDPRESS_DB_USER"
    set_config 'DB_PASSWORD' "$WORDPRESS_DB_PASSWORD"
    set_config 'DB_NAME' "$WORDPRESS_DB_NAME"

    # allow any of these "Authentication Unique Keys and Salts." to be specified via
    # environment variables with a "WORDPRESS_" prefix (ie, "WORDPRESS_AUTH_KEY")
    UNIQUES=(
        AUTH_KEY
        SECURE_AUTH_KEY
        LOGGED_IN_KEY
        NONCE_KEY
        AUTH_SALT
        SECURE_AUTH_SALT
        LOGGED_IN_SALT
        NONCE_SALT
    )
    for unique in "${UNIQUES[@]}"; do
        eval unique_value=\$WORDPRESS_$unique
        if [ "$unique_value" ]; then
            set_config "$unique" "$unique_value"
        else
            # if not specified, let's generate a random value
            current_set="$(sed -rn "s/define\((([\'\"])$unique\2\s*,\s*)(['\"])(.*)\3\);/\4/p" wp-config.php)"
            if [ "$current_set" = 'put your unique phrase here' ]; then
                set_config "$unique" "$(head -c1M /dev/urandom | sha1sum | cut -d' ' -f1)"
            fi
        fi
    done

    if [ "$WORDPRESS_TABLE_PREFIX" ]; then
        set_config '$table_prefix' "$WORDPRESS_TABLE_PREFIX"
    fi

    if [ "$WORDPRESS_DEBUG" ]; then
        set_config 'WP_DEBUG' 1 boolean
    fi

    TERM=dumb php -- "$WORDPRESS_DB_HOST" "$WORDPRESS_DB_USER" "$WORDPRESS_DB_PASSWORD" "$WORDPRESS_DB_NAME" <<'EOPHP'
<?php
// database might not exist, so let's try creating it (just to be safe)

$stderr = fopen('php://stderr', 'w');

list($host, $port) = explode(':', $argv[1], 2);

$maxTries = 10;
do {
    $mysql = new mysqli($host, $argv[2], $argv[3], '', (int)$port);
    if ($mysql->connect_error) {
        fwrite($stderr, "\n" . 'MySQL Connection Error: (' . $mysql->connect_errno . ') ' . $mysql->connect_error . "\n");
        --$maxTries;
        if ($maxTries <= 0) {
            exit(1);
        }
        sleep(3);
    }
} while ($mysql->connect_error);

if (!$mysql->query('CREATE DATABASE IF NOT EXISTS `' . $mysql->real_escape_string($argv[4]) . '`')) {
    fwrite($stderr, "\n" . 'MySQL "CREATE DATABASE" Error: ' . $mysql->error . "\n");
    $mysql->close();
    exit(1);
}

$mysql->close();
EOPHP
fi

exec "$@"