diff --git a/tour/tools/map.sh b/tour/tools/map.sh
index 0f6a0bca95..509bf49e23 100755
--- a/tour/tools/map.sh
+++ b/tour/tools/map.sh
@@ -1,41 +1,38 @@
-#!/bin/sh
+#!/bin/bash
 
-# Copyright 2011 The Go Authors.  All rights reserved.
+# Copyright 2011 The Go Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
 # This code parses mapping.old and finds a correspondence from the old
 # urls (e.g. #42) to the corresponding path (e.g. /concurrency/3).
 
-function findURL {
-	title="$1"
-	file=$(grep -l "* $title\$" *.article)
-	if [[ -z $file ]]
-	then
-		echo "undefined"
-		return 1
-	fi
-	titles=$(grep "^* " $file | awk '{print NR, $0}')
-	page=$(echo "$titles" | grep "* $title\$" | awk '{print $1}')
-	if [[ $(echo "$page" | wc -l) -gt "1" ]]
-	then
-		echo "multiple matches found for $title; find 'CHOOSE BETWEEN' in the output" 1>&2
-		page="CHOOSE BETWEEN $page"
-	fi
-
-	page=$(echo $page)
-	lesson=$(echo "$file" | rev | cut -c 9- | rev)
-	echo "'/$lesson/$page'"
-	return 0
+find_url() {
+    title="$1"
+    file=$(grep -l "* $title$" ./*.article)
+    if [[ -z $file ]]; then
+        echo "undefined" >&2
+        return 1
+    fi
+    titles=$(grep "^* " "$file" | awk '{print NR, $0}')
+    page=$(echo "$titles" | grep "* $title$" | awk '{print $1}')
+    if [[ $(echo "$page" | wc -l) -gt "1" ]]; then
+        echo "multiple matches found for $title; find 'CHOOSE BETWEEN' in the output" >&2
+        page="CHOOSE BETWEEN $page"
+    fi
+    page=$(echo "$page")
+    lesson=$(echo "$file" | sed -E 's|^(.*)/(.*).article$|\2|')
+    echo "'/$lesson/$page'"
+    return 0
 }
 
-mapping=`cat mapping.old`
+mapping=$(cat mapping.old)
 
-pushd ../content
-echo "$mapping" | while read page; do
-	num=$(echo "$page" | awk '{print $1}')
-	title=$(echo "$page" | sed "s/[0-9]* //")
-	url=$(findURL "$title")
-	echo "    '#$num': $url, // $title"
-done
-popd > /dev/null
+cd ../content || exit
+while read -r page; do
+    num=$(echo "$page" | awk '{print $1}')
+    title=$(echo "$page" | cut -d' ' -f2-)
+    url=$(find_url "$title")
+    echo "    '#$num': $url, // $title"
+done <<< "$mapping"
+cd - > /dev/null || exit