diff --git a/README.md b/README.md
index 51dcb66..7008ccc 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,9 @@
 # pkgsync
 A simple script to sync installed packages across Arch installs
 
+# Usage
+Configure pkgsync by modifying /etc/default/pkgsync, follow instructions in comments.  Then just run pkgsync on each system to sync packages.
+
 # Dependencies
 This script is only for Linux distros that use pacman for package management.  All dependencies are included in the Arch Linux base group but are listed out here for general info:
 
diff --git a/config/pkgsync b/config/pkgsync
index 27c700a..c5f63a7 100644
--- a/config/pkgsync
+++ b/config/pkgsync
@@ -1,6 +1,8 @@
 # this is the configuration for pkgsync
 # it uses these defaults, but you can change them
 
+# list files can have comments starting with #, and do not need to be sorted
+
 # packages on this system to exclude from shared install list
 #EXCLUSION_LIST=/etc/pkgsync/pkg_exclude.list
 
@@ -13,6 +15,11 @@
 # packages to install on all systems, you must sync it between systems
 #INSTALL_LIST=/etc/pkgsync/pkg_install.list
 
+# scripts must be executable and have non-zero exit status for pkgsync to continue
+
+# script that is ran before pkgsync calculations start, can be used to sync various lists
+#PRESTART_SCRIPT=/etc/pkgsync/pkg_prestart.sh
+
 # script that is ran when INSTALL_LIST is changed, can be used to sync it
 #FINISH_SCRIPT=/etc/pkgsync/pkg_finish.sh
 
diff --git a/pkgsync b/pkgsync
index 5351d9b..74e841b 100755
--- a/pkgsync
+++ b/pkgsync
@@ -8,17 +8,20 @@ EXCLUSION_LIST="${EXCLUSION_LIST:-/etc/pkgsync/pkg_exclude.list}"
 BLACKLIST_LIST="${BLACKLIST_LIST:-/etc/pkgsync/pkg_blacklist.list}"
 REMOVE_LIST="${REMOVE_LIST:-/etc/pkgsync/pkg_remove.list}"
 INSTALL_LIST="${INSTALL_LIST:-/etc/pkgsync/pkg_install.list}"
-FINISH_SCRIPT="${INSTALL_LIST:-/etc/pkgsync/pkg_finish.sh}"
+PRESTART_SCRIPT="${PRESTART_SCRIPT:-/etc/pkgsync/pkg_prestart.sh}"
+FINISH_SCRIPT="${FINISH_SCRIPT:-/etc/pkgsync/pkg_finish.sh}"
 TMP_DIR="${TMP_DIR:-/tmp}"
 
+[ -x "$PRESTART_SCRIPT" ] && "$PRESTART_SCRIPT"
+
 # we really don't care if these exist or not or are empty, we just want empty files if so
-grep -v '^#' "$EXCLUSION_LIST" 2>/dev/null > "$TMP_DIR/pkg_exclude.list" || true
-grep -v '^#' "$BLACKLIST_LIST" 2>/dev/null > "$TMP_DIR/pkg_blacklist.list" || true
-grep -v '^#' "$REMOVE_LIST" 2>/dev/null > "$TMP_DIR/pkg_remove.list" || true
-[ ! -e "$INSTALL_LIST" ] && touch "$INSTALL_LIST"
+grep -v '^#' "$EXCLUSION_LIST" 2>/dev/null | sort -u > "$TMP_DIR/pkg_exclude.list"   || true
+grep -v '^#' "$BLACKLIST_LIST" 2>/dev/null | sort -u > "$TMP_DIR/pkg_blacklist.list" || true
+grep -v '^#' "$REMOVE_LIST"    2>/dev/null | sort -u > "$TMP_DIR/pkg_remove.list"    || true
+grep -v '^#' "$INSTALL_LIST"   2>/dev/null | sort -u > "$TMP_DIR/pkg_install.list"   || true
 
 # get our explicitly installed packages, minus hardware-specific exclusions
-pacman -Qe | awk '{print $1}' | sort | comm -23 - "$TMP_DIR/pkg_exclude.list" > "$TMP_DIR/mypkgs_with_exclusions.txt"
+pacman -Q | awk '{print $1}' | sort | comm -23 - "$TMP_DIR/pkg_exclude.list" > "$TMP_DIR/mypkgs_with_exclusions.txt"
 
 # exclude packages to remove
 comm -23 "$TMP_DIR/mypkgs_with_exclusions.txt" "$TMP_DIR/pkg_remove.list" > "$TMP_DIR/mypkgs_with_exclusions_without_remove.txt"
@@ -27,24 +30,55 @@ comm -23 "$TMP_DIR/mypkgs_with_exclusions.txt" "$TMP_DIR/pkg_remove.list" > "$TM
 comm -12 "$TMP_DIR/mypkgs_with_exclusions.txt" "$TMP_DIR/pkg_remove.list" > "$TMP_DIR/pkg_toremove.list"
 
 # combine our packages with shared installed list, excluding remove
-sort -u "$TMP_DIR/mypkgs_with_exclusions_without_remove.txt" "$INSTALL_LIST" | comm -23 - "$TMP_DIR/pkg_remove.list" > "$TMP_DIR/pkg_installed.list"
+sort -u "$TMP_DIR/mypkgs_with_exclusions_without_remove.txt" "$TMP_DIR/pkg_install.list" | comm -23 - "$TMP_DIR/pkg_remove.list" > "$TMP_DIR/pkg_installed.list"
 
 # list of packages to install, with our blacklist excluded
 comm -13 "$TMP_DIR/mypkgs_with_exclusions_without_remove.txt" "$TMP_DIR/pkg_installed.list" | comm -23 - "$TMP_DIR/pkg_blacklist.list" > "$TMP_DIR/pkg_toinstall.list"
 
+# packages already on this computer not in the shared install list we need to put in there
+comm -23 "$TMP_DIR/pkg_installed.list" "$TMP_DIR/pkg_install.list" > "$TMP_DIR/pkg_ourinstall.list"
+
 # offer to install missing packages
-xargs -p --no-run-if-empty pacman -S --needed --noconfirm < "$TMP_DIR/pkg_toinstall.list"
+if [ -s "$TMP_DIR/pkg_toinstall.list" ]
+then
+    yn=l
+    while [[ ! "$yn" =~ ^[YyNnAa]$ ]]
+    do
+        read -p "Install new packages? (yes/no/list/abort)..." -n 1 yn
+        echo
+        [[ "$yn" =~ ^[Ll]$ ]] && cat "$TMP_DIR/pkg_toinstall.list"
+    done
+    [[ "$yn" =~ ^[Yy]$ ]] && pacman -S --needed --confirm - < "$TMP_DIR/pkg_toinstall.list"
+    [[ "$yn" =~ ^[Aa]$ ]] && exit 1
+fi
 
 # offer to remove packages
-xargs -p --no-run-if-empty pacman -Ru --noconfirm < "$TMP_DIR/pkg_toremove.list"
+if [ -s "$TMP_DIR/pkg_toremove.list" ]
+then
+    yn=l
+    while [[ ! "$yn" =~ ^[YyNnAa]$ ]]
+    do
+        read -p "Remove packages? (yes/no/list/abort)..." -n 1 yn
+        echo
+        [[ "$yn" =~ ^[Ll]$ ]] && cat "$TMP_DIR/pkg_toremove.list"
+    done
+    [[ "$yn" =~ ^[Yy]$ ]] && pacman -Ru --confirm - < "$TMP_DIR/pkg_toremove.list"
+    [[ "$yn" =~ ^[Aa]$ ]] && exit 1
+fi
 
 # offer to update install list, if it changed
-if [ "$(comm -3 "$TMP_DIR/pkg_installed.list" "$INSTALL_LIST")" != "" ]
+if [ -s "$TMP_DIR/pkg_ourinstall.list" ]
 then
-    read -p "Overwrite '$INSTALL_LIST' with new package list and run finish script?..." -n 1 yn
-    [[ $yn =~ ^[Yy]$ ]] && cp "$TMP_DIR/pkg_installed.list" "$INSTALL_LIST"
-    echo
+    yn=l
+    while [[ ! "$yn" =~ ^[YyNnAa]$ ]]
+    do
+        read -p "Append packages unique to this computer to install list and run finish script? (yes/no/list/abort)..." -n 1 yn
+        echo
+        [[ "$yn" =~ ^[Ll]$ ]] && cat "$TMP_DIR/pkg_ourinstall.list"
+    done
+    [[ "$yn" =~ ^[Yy]$ ]] && cat "$TMP_DIR/pkg_ourinstall.list" >> "$INSTALL_LIST"
+    [[ "$yn" =~ ^[Aa]$ ]] && exit 1
     [ -x "$FINISH_SCRIPT" ] && "$FINISH_SCRIPT"
 fi
 
-rm -f "$TMP_DIR/pkg_exclude.list" "$TMP_DIR/pkg_blacklist.list" "$TMP_DIR/pkg_remove.list" "$TMP_DIR/mypkgs_with_exclusions.txt" "$TMP_DIR/mypkgs_with_exclusions_without_remove.txt" "$TMP_DIR/pkg_toremove.list" "$TMP_DIR/pkg_installed.list" "$TMP_DIR/pkg_toinstall.list"
+rm -f "$TMP_DIR/pkg_exclude.list" "$TMP_DIR/pkg_blacklist.list" "$TMP_DIR/pkg_remove.list" "$TMP_DIR/mypkgs_with_exclusions.txt" "$TMP_DIR/mypkgs_with_exclusions_without_remove.txt" "$TMP_DIR/pkg_toremove.list" "$TMP_DIR/pkg_installed.list" "$TMP_DIR/pkg_toinstall.list" "$TMP_DIR/pkg_ourinstall.list"