*: Move die() into .local/bin/helpers.sh

The function `die` was redundantly implemented in various files.

Move the function into .local/bin/helpers.sh and source that where
previously implemented.

Also prepend the program's name to the message and always terminate the
message with a newline. The newline was previously needed for a small
but unnecessary hack that prevented the need of the `[ -z "$1" ]` test.

.local/bin/filterHistory

@@ -8,14 +8,12 @@
 ##   format of zshs extended history.
 ## An automatic backup is created before deleting that can be used for recovery.
 
-die() {
-	printf "$1" >&2
-	exit ${2:-1}
-}
+# Source die()
+. "$HOME"/.local/bin/helpers.sh
 
-[[ $# -eq 1 ]] || die "Specify a history file.\n"
-[[ -e "$1" ]] || die "File does not exist.\n"
-[[ "$(stat -c '%a' "$1")" = "600" ]] || die "File permissions are off.\n"
+[[ $# -eq 1 ]] || die "Specify a history file."
+[[ -e "$1" ]] || die "File does not exist."
+[[ "$(stat -c '%a' "$1")" = "600" ]] || die "File permissions are off."
 
 # Take a history file per stdin and sort the commands per number of occurrences
 hist-sort() {

.local/bin/helpers.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+#
+# A collection of useful shell functions. This file should be sourced, rather
+# than executed.
+
+
+# Print error message, prepended by the programs name, and then exit
+#
+# Usage: die [<MESSAGE>] [<EXIT_CODE>]
+die() {
+	[ -z "$1" ] || >&2 printf "%s: %s\n" "$0" "$1"
+	exit ${2:-1}
+}