Move depencies checking before args parsing

This commit also adds bc(1) to the dependencies
list and fixed some comments.

kvmstats

@@ -1,16 +1,25 @@
 #!/bin/sh
 
-# NOTE: kvmstats relies on the hxselect command to parse virsh' xml
+# NOTE: kvmstats relies on the hxselect(1) command to parse virsh' xml
 # files. On Debian, this command is provided by the 'html-xml-utils'
 # package.
 
 set -e -u
 
 usage () {
-    echo 'usage: kvmstats.sh [-u K|M|G]'
+    echo 'usage: kvmstats.sh [-a] [-u K|M|G]'
     exit 1
 }
 
+for DEP in hxselect lvs tempfile bc
+do
+    if [ -z "$(which $DEP)" ]
+    then
+        echo "kvmstats.sh: $DEP not found in \$PATH" 1>&2
+        exit 1
+    fi
+done
+
 POW=$(echo 1024 ^ 3 | bc)
 while [ $# -ne 0 ] && echo "$1" | grep -q '^-[[:alnum:]]'
 do
@@ -42,15 +51,6 @@ done
 # since libvirt seems to store memoy in KiB, POW must be lowered by 1
 POW=$((POW / 1024))
 
-for DEP in hxselect lvs tempfile
-do
-    if [ -z "$(which $DEP)" ]
-    then
-        echo "kvmstats.sh: $DEP not found in \$PATH" 1>&2
-        exit 1
-    fi
-done
-
 TMPFILE=$(tempfile -s kvmstats)
 LVSOUT=$(tempfile -s kvmstats)