docker_compose查看指定服务下的环境变量信息:

在docker-compsoe.yml同级目录下执行
$ docker-compose config
可以查看所有 service 的配置信息，比如引用了哪些环境变量
  
查看单个容器的环境变量:
$ docker exec -it k8s-dev-v2-php env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=49c87b3bc8b9
TERM=xterm
MAIL_NAME=k8s-dev-v2-mailcatcher
MAIL_SMTP_PORT=1025
PHPIZE_DEPS=autoconf    dpkg-dev    file    g++     gcc     libc-dev    make    pkg-config    re2c
PHP_INI_DIR=/usr/local/etc/php
PHP_CFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
PHP_CPPFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
PHP_LDFLAGS=-Wl,-O1 -pie
GPG_KEYS=1198C0117593497A5EC5C199286AF1F9897469DC C28D937575603EB4ABB725861C0779DC5C0A9DE4 AFD8691FDAEDF03BDF6E460563F15A9B715376CA
PHP_VERSION=8.3.0alpha1
PHP_URL=https://downloads.php.net/~jakub/php-8.3.0alpha1.tar.xz
PHP_ASC_URL=https://downloads.php.net/~jakub/php-8.3.0alpha1.tar.xz.asc
PHP_SHA256=7df01cbae615cccdc01a811094a74326119080e1141988fd57aeefd6b751165c
HOME=/root
  
对于特定的环境变量:
$ docker exec -it k8s-dev-v2-php printenv PHP_VERSION
8.3.0alpha1
  
当然也可以通过bash进入container，然后访问环境变量:
$ docker exec -it k8s-dev-v2-php bash
root@49c87b3bc8b9:/var/www# printenv
HOSTNAME=49c87b3bc8b9
PHP_VERSION=8.3.0alpha1
PHP_INI_DIR=/usr/local/etc/php
GPG_KEYS=1198C0117593497A5EC5C199286AF1F9897469DC C28D937575603EB4ABB725861C0779DC5C0A9DE4 AFD8691FDAEDF03BDF6E460563F15A9B715376CA
PHP_LDFLAGS=-Wl,-O1 -pie
MAIL_SMTP_PORT=1025
PWD=/var/www
HOME=/root
PHP_SHA256=7df01cbae615cccdc01a811094a74326119080e1141988fd57aeefd6b751165c
PHPIZE_DEPS=autoconf    dpkg-dev    file    g++     gcc     libc-dev    make    pkg-config    re2c
TERM=xterm
PHP_URL=https://downloads.php.net/~jakub/php-8.3.0alpha1.tar.xz
SHLVL=1
PHP_CFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MAIL_NAME=k8s-dev-v2-mailcatcher
PHP_ASC_URL=https://downloads.php.net/~jakub/php-8.3.0alpha1.tar.xz.asc
PHP_CPPFLAGS=-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
_=/usr/bin/printenv 
  
root@49c87b3bc8b9:/var/www# echo $PHP_VERSION
8.3.0alpha1
  
也可以直接通过 env 命令 访问全部环境变量，通过 sort 排序: