Add dependencies to readme

Makefile

@@ -20,7 +20,6 @@ PREFIX ?= /usr
 SNAPPER_CONFIG ?= /etc/sysconfig/snapper
 
 BIN_DIR = $(DESTDIR)$(PREFIX)/bin
-SYSTEMD_DIR = $(DESTDIR)$(PREFIX)/lib/systemd/system
 SHARE_DIR = $(DESTDIR)$(PREFIX)/share
 
 .PHONY: install

README.md

@@ -39,6 +39,28 @@ Starting with release 0.6, the tarballs are signed with my key with fingerprint
 `F7B28C61944FE30DABEEB0B01070BCC98C18BD66` ([public key]). Previous tarballs and commits
 used a different key with fingerprint `8535CEF3F3C38EE69555BF67E4B5E45AA3B8C5C3`.
 
+## Dependencies
+
+### Mandatory dependencies:
+
+The dependencies below are Arch Linux package names. Packages on other distros may use different names.
+
+* bash
+* btrfs-progs
+* coreutils (for `cat`/`cp`/`sync`)
+* gawk
+* grep
+* snapper
+* util-linux (for `findmnt`)
+
+### Optional dependencies:
+
+* libnotify (for desktop notifications)
+* openssh (for remote backups)
+* pv (for progress bar during backup)
+* rsync (for remote backups)
+* sudo (for desktop notifications)
+
 ## Documentation
 
 See `snap-sync(8)` after installation.

bin/snap-sync

@@ -37,12 +37,12 @@ printf "snap-sync comes with ABSOLUTELY NO WARRANTY. This is free software, and
 SNAPPER_CONFIG=/etc/conf.d/snapper
 
 donotify=0
-if ! which notify-send &> /dev/null; then
+if ! command -v notify-send &> /dev/null; then
     donotify=1
 fi
 
 doprogress=0
-if ! which pv &> /dev/null; then
+if ! command -v pv &> /dev/null; then
     doprogress=1
 fi
 
@@ -84,7 +84,7 @@ Options:
  -n, --noconfirm          do not ask for confirmation
  -k, --keepold            keep old incremental snapshots instead of deleting them
                           after backup is performed
- -p, --port <port>        remote port; wsed with '--remote'.
+ -p, --port <port>        remote port; used with '--remote'.
  -q, --quiet              do not send notifications; instead print them.
  -r, --remote <address>   ip address of a remote machine to backup to
  --sudo                   use sudo on the remote machine
@@ -182,6 +182,12 @@ uuid_cmdline=${uuid_cmdline:-"none"}
 subvolid_cmdline=${subvolid_cmdline:-"5"}
 noconfirm=${noconfirm:-"no"}
 
+if [[ -z $remote ]]; then
+    if ! command -v rsync &> /dev/null; then
+        die "--remote specified but rsync command not found"
+    fi
+fi
+
 if [[ "$uuid_cmdline" != "none" ]]; then
     if [[ -z $remote ]]; then
         notify_info "Backup started" "Starting backups to $uuid_cmdline subvolid=$subvolid_cmdline..."