From bb2c469018ad92749e0d9a3068099dd1b21accf3 Mon Sep 17 00:00:00 2001
From: Tianon Gravi <admwiggin@gmail.com>
Date: Mon, 1 Aug 2016 17:03:07 -0700
Subject: [PATCH] Convert explicit "export A=B" lines of Apache's envvars file
 into "${A:=B}" such that we can override them at runtime easily

Before:

```sh
unset HOME

if [ "${APACHE_CONFDIR##/etc/apache2-}" != "${APACHE_CONFDIR}" ] ; then
	SUFFIX="-${APACHE_CONFDIR##/etc/apache2-}"
else
	SUFFIX=
fi

export APACHE_RUN_USER=www-data
export APACHE_RUN_GROUP=www-data
export APACHE_PID_FILE=/var/run/apache2/apache2$SUFFIX.pid
export APACHE_RUN_DIR=/var/run/apache2$SUFFIX
export APACHE_LOCK_DIR=/var/lock/apache2$SUFFIX
export APACHE_LOG_DIR=/var/log/apache2$SUFFIX

export LANG=C

export LANG
```

After:

```sh
unset HOME

if [ "${APACHE_CONFDIR##/etc/apache2-}" != "${APACHE_CONFDIR}" ] ; then
	SUFFIX="-${APACHE_CONFDIR##/etc/apache2-}"
else
	SUFFIX=
fi

: ${APACHE_RUN_USER:=www-data}
export APACHE_RUN_USER
: ${APACHE_RUN_GROUP:=www-data}
export APACHE_RUN_GROUP
: ${APACHE_PID_FILE:=/var/run/apache2/apache2$SUFFIX.pid}
export APACHE_PID_FILE
: ${APACHE_RUN_DIR:=/var/run/apache2$SUFFIX}
export APACHE_RUN_DIR
: ${APACHE_LOCK_DIR:=/var/lock/apache2$SUFFIX}
export APACHE_LOCK_DIR
: ${APACHE_LOG_DIR:=/var/log/apache2$SUFFIX}
export APACHE_LOG_DIR

: ${LANG:=C}
export LANG

export LANG
```

(minus comments)
---
 apache-Dockerfile-block-1 | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/apache-Dockerfile-block-1 b/apache-Dockerfile-block-1
index 5ca40243..f0a1699c 100644
--- a/apache-Dockerfile-block-1
+++ b/apache-Dockerfile-block-1
@@ -3,8 +3,17 @@ RUN apt-get update && apt-get install -y apache2-bin apache2.2-common --no-insta
 ENV APACHE_CONFDIR /etc/apache2
 ENV APACHE_ENVVARS $APACHE_CONFDIR/envvars
 
-# setup directories and permissions
 RUN set -ex \
+	\
+# generically convert lines like
+#   export APACHE_RUN_USER=www-data
+# into
+#   : ${APACHE_RUN_USER:=www-data}
+#   export APACHE_RUN_USER
+# so that they can be overridden at runtime ("-e APACHE_RUN_USER=...")
+	&& sed -r 's/^export ([^=]+)=(.*)$/: ${\1:=\2}\nexport \1/' "$APACHE_ENVVARS" \
+	\
+# setup directories and permissions
 	&& . "$APACHE_ENVVARS" \
 	&& for dir in \
 		"$APACHE_LOCK_DIR" \