Support for alpine linux

rebased on dev
replaces #1047

update.sh

@@ -1,10 +1,13 @@
 #!/bin/bash
 
+#exit on error and pipefail
+set -o errexit
+set -o pipefail
+
 for bin in curl docker-compose docker git awk sha1sum; do
   if [[ -z $(which ${bin}) ]]; then echo "Cannot find ${bin}, exiting..."; exit 1; fi
 done
 
-set -o pipefail
 export LC_ALL=C
 DATE=$(date +%Y-%m-%d_%H_%M_%S)
 BRANCH=$(git rev-parse --abbrev-ref HEAD)
@@ -30,6 +33,9 @@ done
 
 [[ ! -f mailcow.conf ]] && { echo "mailcow.conf is missing"; exit 1;}
 
+if grep --help 2>&1 | head -n 1 | grep -q -i "busybox"; then echo "BusybBox grep detected, please install gnu grep, \"apk add --no-cache --upgrade grep\""; exit 1; fi
+if cp --help 2>&1 | head -n 1 | grep -q -i "busybox"; then echo "BusybBox cp detected, please install coreutils, \"apk add --no-cache --upgrade coreutils\""; exit 1; fi
+
 CONFIG_ARRAY=(
   "SKIP_LETS_ENCRYPT"
   "USE_WATCHDOG"
@@ -118,7 +124,7 @@ curl -o /dev/null google.com -sm3
 if [[ $? != 0 ]]; then
   echo -e "\e[31mfailed\e[0m"
   exit 1
-  else
+else
   echo -e "\e[32mOK\e[0m"
 fi
 
@@ -135,7 +141,7 @@ fi
 
 if [[ -f mailcow.conf ]]; then
   source mailcow.conf
-  else
+else
   echo -e "\e[31mNo mailcow.conf - is mailcow installed?\e[0m"
   exit 1
 fi
@@ -183,11 +189,14 @@ fi
 
 echo -e "\e[32mFetching new docker-compose version...\e[0m"
 sleep 2
-if [[ $(curl -sL -w "%{http_code}" https://www.servercow.de/docker-compose/latest.php -o /dev/null) == "200" ]]; then
+if [[ ! -z $(which pip) && $(pip list --local | grep -c docker-compose) == 1 ]]; then
+  true
+  #prevent breaking a working docker-compose installed with pip
+elif [[ $(curl -sL -w "%{http_code}" https://www.servercow.de/docker-compose/latest.php -o /dev/null) == "200" ]]; then
   LATEST_COMPOSE=$(curl -#L https://www.servercow.de/docker-compose/latest.php)
   curl -#L https://github.com/docker/compose/releases/download/${LATEST_COMPOSE}/docker-compose-$(uname -s)-$(uname -m) > $(which docker-compose)
   chmod +x $(which docker-compose)
-  else
+else
   echo -e "\e[33mCannot determine latest docker-compose version, skipping...\e[0m"
 fi