feat(script): Introduce dry-run option (#1)

README.md

@@ -21,7 +21,7 @@ Get started like so:
     sudo ln -s <repo>/pacman-zfs-snapshot.conf /etc/pacman-zfs-snapshot.conf
     ```
     Note that while you may choose arbitrary locations for symlinks the `pacman-zfs-snapshot.hook` file references `/usr/local/bin/pacman-zfs-snapshot`. Change that accordingly if you need to.
-1. Adjust `pacman-zfs-snapshot.conf` to your liking
+1. Adjust `pacman-zfs-snapshot.conf` to your liking. You may want to set `do_dry_run='true'` for a start and just reinstall a benign package to get a feel for what this hook would do.
 1. For datasets you want auto-snapshotted add property `space.quico:auto-snapshot=true`
     ```
     zfs set space.quico:auto-snapshot=true zpool/root/archlinux

pacman-zfs-snapshot.conf

@@ -1,3 +1,5 @@
+do_dry_run='true'
+
 # Pipe-separated list of kernel names. Will be matched against regular
 # expression ^this_var_here$. Snapshots taken before a pacman transaction on
 # an important package have a separate retention from snapshots for trivial

pacman-zfs-snapshot.sh

@@ -16,6 +16,7 @@ if [[ -r "${conf_file}" ]]; then
     source "${conf_file}"
 fi
 
+if [[ ! "${do_dry_run}" ]]; then do_dry_run='true'; fi
 if [[ ! "${important_names}" ]]; then important_names='linux'; fi
 if [[ ! "${snaps_trivial_keep}" ]]; then snaps_trivial_keep='5'; fi
 if [[ ! "${snaps_important_keep}" ]]; then snaps_important_keep='5'; fi