KERNEL_VERSION=$( readlink /boot/vmlinuz-generic | rev | cut -f1 -d- | rev )
OUTPUT_IMAGE="/boot/initrd-${KERNEL_VERSION}.gz

$ mkinitrd -F -c

$ mkinitrd -F -c -k 4.4.70-prod

$ mkinitrd -o /tmp/initrd-%KVER%.gz
33751 blocks
/tmp/initrd-4.4.75.gz created.
Be sure to run lilo again if you use it.

$ mkinitrd -o /tmp/initrd-%KVER%_%SLACKVER%.gz
33751 blocks
/tmp/initrd-4.4.75_14.2.gz created.
Be sure to run lilo again if you use it.


$ cat /etc/mkinitrd.conf | grep OUTPUT_IMAGE
OUTPUT_IMAGE=/boot/%KVER%-initrd-generic-%SLACKVER%.gz

$ mkinitrd -k 4.4.75-custom -F
33751 blocks
/boot/4.4.75-custom-initrd-generic-14.2.gz created.
Be sure to run lilo again if you use it.

$ OUTPUT_IMAGE=/tmp/my-initrd-for-%KVER%-on-slackware-%SLACKVER%.gz ./mkinitrd -k 4.4.75
33751 blocks
/tmp/my-initrd-for-4.4.75-on-slackware-14.2.gz created.
Be sure to run lilo again if you use it.

--- mkinitrd.orig	2017-07-11 10:24:41.580285638 +0200
+++ mkinitrd	2017-07-11 11:26:00.768449804 +0200
@@ -261,7 +261,19 @@
   cp -a /etc/modprobe.d $SOURCE_TREE/etc
   cp -a /lib/modprobe.d $SOURCE_TREE/lib/
 }
-     
+
+# Normalize the string $1 by replacing occurences of 
+# recognized tags by their current values.
+#
+# this version take the following tags into account:
+#  %KVER% (kernel version)
+#  %SLACKVER% (slackware version)
+#
+function normalize_string() {
+  echo "$1" | sed -e "s?%KVER%?${KERNEL_VERSION}?g" \
+                  -e "s?%SLACKVER%?$(cat /etc/slackware-version|cut -f2 -d" ")?g"
+}
+
 # If --help is given, print_usage and exit:
 if echo $* | grep -wq '\--help' ; then
   print_usage
@@ -285,7 +297,7 @@
 # Default actions without options:
 if [ -z "$1" ]; then
   # We need a sensible default for this special case:
-  OUTPUT_IMAGE=${OUTPUT_IMAGE:-/boot/initrd.gz}
+  OUTPUT_IMAGE=$(normalize_string ${OUTPUT_IMAGE:-/boot/initrd.gz})
   # If the output tree doesn't exist, create it and then exit:
   if [ ! -d $SOURCE_TREE ]; then
     echo "Nothing found at location $SOURCE_TREE, so we will create an"
@@ -349,7 +361,7 @@
       ;;
     -o)
       # canonicalize filename:
-      OUTPUT_IMAGE="$(readlink -m $2)"
+      OUTPUT_IMAGE="$(readlink -m $(normalize_string $2))"
       shift 2
       ;;
     -r)
@@ -465,7 +477,7 @@
 fi
 
 # If no OUTPUT_IMAGE was specified, read it from the SOURCE_TREE if possible:
-OUTPUT_IMAGE=${OUTPUT_IMAGE:-"$(cat $SOURCE_TREE/initrd-name)"}
+OUTPUT_IMAGE=$(normalize_string ${OUTPUT_IMAGE:-"$(cat $SOURCE_TREE/initrd-name)"})
 # If we still have no value, apply the default:
 OUTPUT_IMAGE=${OUTPUT_IMAGE:-"/boot/initrd.gz"}
 # Finally, write the image name into the SOURCE_TREE: