community/apk-post-messages: posix compliant script

Also fixes a number of edge cases.

community/apk-post-messages/APKBUILD

 # Contributor: Stuart Cardall <developer@it-offshore.co.uk>
 # Maintainer: Stuart Cardall <developer@it-offshore.co.uk>
 pkgname=apk-post-messages
-pkgver=0.10
-pkgrel=1
+pkgver=0.11
+pkgrel=0
 pkgdesc="Print apk post-install messages"
 url="https://alpinelinux.org"
 arch="noarch"

community/apk-post-messages/apk-post-messages.trigger

@@ -4,13 +4,12 @@ x=README.alpine
 for i; do
 	if [ -f "$i/$x" ]; then
 		msg="| $i: $x |"
-		msg_len=$(( $(echo $msg |wc -m) - 1))
+		msg_len=$(printf '%s' "$msg" | wc -m)
 		printf "%${msg_len}s" | sed 's/ /-/g'
-		echo -e "\n$msg"
+		printf '\n%s\n' "$msg"
 		printf "%${msg_len}s" | sed 's/ /=/g'
-		echo -e "\n"
-		cat $i/$x
-		echo -e; break
+		printf '\n\n'
+		cat -- "$i/$x"
+		printf '\n'
 	fi
 done
-