Change ifinstalled script to exist

Renamed ifinstalled to exist, moved it into base shell module. It can be
called with just a command name to check for, or with an additional
libnotify urgency level (low, normal, critical).

If called with an urgency as the second argument, the user will be
notified of the missing command with the corresponding urgency.

scripts/.local/bin/ifinstalled

@@ -1,4 +0,0 @@
-#!/usr/bin/env sh
-# If $1 command is not available, error code and notify.
-
-command -v "$1" >/dev/null || { notify-send "📦 $1" "must be installed for this function." && exit 1 ;}

sh/.local/bin/exist

@@ -0,0 +1,17 @@
+#!/usr/bin/env sh
+# check for existing implementations
+# If $1 command is not available, error code
+# If $2 is low, normal, urgent, also notify the user. (loud-mode)
+
+if command -v "$1" >/dev/null; then
+  exit 0
+else
+  if [ -n "$2" ]; then
+    if command -v notify-send >/dev/null; then
+      notify-send "📦 $1" --urgency="$2" "must be installed for this function."
+    else
+      printf "%s: 📦 %s must be installed for this function.\n" "$2" "$1"
+    fi
+  fi
+  exit 1
+fi