rewrite scripts

try to provide better syntax and avoid using bash

debian/linux-perf.postrm

@@ -2,21 +2,24 @@
 
 set -e
 
-old_version_suffix="$(echo "$2" | sed -rn 's/^([0-9]+\.[0-9]+).*/\1/p')"
-if [ "$old_version_suffix" ]; then
+old_version_suffix=$(printf '%s' "$2" | sed -En 's/^([0-9]+\.[0-9]+).*/\1/p')
+if [ -n "${old_version_suffix}" ] ; then
     dpkg-maintscript-helper symlink_to_dir \
-	/usr/share/doc/linux-perf "linux-perf-${old_version_suffix}" 5.16\~rc8-1\~exp1 linux-perf -- "$@"
+      /usr/share/doc/linux-perf "linux-perf-${old_version_suffix}" '5.16~rc8-1~exp1' linux-perf -- "$@"
 fi
+unset old_version_suffix
 
-if [ "$1" = remove ]
-then
-	for wrapper in /usr/bin/perf \
-		       /usr/share/bash-completion/completions/perf \
-		       /usr/share/man/man1/perf.1.gz; do
-	    diversion="${wrapper%/perf*}/perf.wrapper${wrapper#*/perf}"
-	    dpkg-divert --package linux-perf --divert "$diversion" --rename \
-		--remove "$wrapper"
-	done
-fi
+case "$1" in
+remove )
+    for wrapper in \
+      /usr/bin/perf \
+      /usr/share/bash-completion/completions/perf \
+      /usr/share/man/man1/perf.1.gz \
+    ; do
+        diversion="${wrapper%/perf*}/perf.wrapper${wrapper#*/perf}"
+        dpkg-divert --package linux-perf --divert "${diversion}" --rename --remove "${wrapper}"
+    done ; unset wrapper diversion
+;;
+esac
 
 #DEBHELPER#