diff --git a/gh-md-toc b/gh-md-toc
index 35239bf..d8dc492 100755
--- a/gh-md-toc
+++ b/gh-md-toc
@@ -52,6 +52,7 @@ gh_toc_load() {
 gh_toc_md2html() {
     local gh_file_md=$1
     local skip_header=$2
+    local status
 
     URL=https://api.github.com/markdown/raw
 
@@ -70,9 +71,9 @@ gh_toc_md2html() {
     local gh_tmp_file_md=$gh_file_md
     if [ "$skip_header" = "yes" ]; then
         if grep -Fxq "<!--te-->" "$gh_src"; then
-          # cut everything before the toc
-          gh_tmp_file_md=$gh_file_md~~
-          sed '1,/<!--te-->/d' "$gh_file_md" > "$gh_tmp_file_md"
+            # cut everything before the toc
+            gh_tmp_file_md=$gh_file_md~~
+            sed '1,/<!--te-->/d' "$gh_file_md" >"$gh_tmp_file_md"
         fi
     fi
 
@@ -83,36 +84,39 @@ gh_toc_md2html() {
         -H "Content-Type:text/plain" \
         -H "$AUTHORIZATION" \
         "$URL")
+    status=$?
 
     rm -f "${gh_file_md}~~"
 
-    if [ "$?" != "0" ]; then
+    if [ "$status" != "0" ]; then
         echo "XXNetworkErrorXX"
-    fi
-    if [ "$(echo "${OUTPUT}" | awk '/API rate limit exceeded/')" != "" ]; then
+    elif [ "$(echo "${OUTPUT}" | awk '/API rate limit exceeded/')" != "" ]; then
         echo "XXRateLimitXX"
+    elif [ "$(echo "${OUTPUT}" | awk '/Bad credentials/')" != "" ]; then
+        echo "XXBadCredentialsXX"
     else
         echo "${OUTPUT}"
     fi
 }
 
-
 #
 # Is passed string url
 #
 gh_is_url() {
     case $1 in
-        https* | http*)
-            echo "yes";;
-        *)
-            echo "no";;
+    https* | http*)
+        echo "yes"
+        ;;
+    *)
+        echo "no"
+        ;;
     esac
 }
 
 #
 # TOC generator
 #
-gh_toc(){
+gh_toc() {
     local gh_src=$1
     local gh_src_copy=$1
     local gh_ttl_docs=$2
@@ -127,7 +131,6 @@ gh_toc(){
         exit 1
     fi
 
-
     # Show "TOC" string only if working with one document
     if [ "$gh_ttl_docs" = "1" ]; then
 
@@ -155,19 +158,32 @@ gh_toc(){
         local rawhtml
         rawhtml=$(gh_toc_md2html "$gh_src" "$skip_header")
         if [ "$rawhtml" == "XXNetworkErrorXX" ]; then
-             echo "Parsing local markdown file requires access to github API"
-             echo "Please make sure curl is installed and check your network connectivity"
-             exit 1
-        fi
-        if [ "$rawhtml" == "XXRateLimitXX" ]; then
-             echo "Parsing local markdown file requires access to github API"
-             echo "Error: You exceeded the hourly limit. See: https://developer.github.com/v3/#rate-limiting"
-             TOKEN_FILE="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/token.txt"
-             echo "or place GitHub auth token here: ${TOKEN_FILE}"
-             exit 1
+            echo "Parsing local markdown file requires access to github API"
+            echo "Please make sure curl is installed and check your network connectivity"
+            exit 1
+        elif [ "$rawhtml" == "XXRateLimitXX" ]; then
+            echo "Parsing local markdown file requires access to github API"
+            echo "Error: You exceeded the hourly limit. See: https://developer.github.com/v3/#rate-limiting"
+            if [ -n "$GH_TOC_TOKEN" ]; then
+                echo "Verify correct GitHub auth token in GH_TOC_TOKEN environment variable"
+            else
+                TOKEN_FILE="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/token.txt"
+                echo "Verify correct GitHub auth token here: ${TOKEN_FILE}"
+            fi
+            exit 1
+        elif [ "$rawhtml" == "XXBadCredentialsXX" ]; then
+            echo "Parsing local markdown file requires access to github API"
+            echo "Error: You provided bad credentials. See: https://developer.github.com/v3/#rate-limiting"
+            if [ -n "$GH_TOC_TOKEN" ]; then
+                echo "Verify correct GitHub auth token in GH_TOC_TOKEN environment variable"
+            else
+                TOKEN_FILE="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/token.txt"
+                echo "Verify correct GitHub auth token here: ${TOKEN_FILE}"
+            fi
+            exit 1
         fi
         local toc
-        toc=`echo "$rawhtml" | gh_toc_grab "$gh_src_copy" "$indent"`
+        toc=$(echo "$rawhtml" | gh_toc_grab "$gh_src_copy" "$indent")
         echo "$toc"
         if [ "$need_replace" = "yes" ]; then
             if grep -Fxq "<!--ts-->" "$gh_src" && grep -Fxq "<!--te-->" "$gh_src"; then
@@ -184,18 +200,18 @@ gh_toc(){
             local toc_path="${gh_src}.toc.${dt}"
             local toc_createdby="<!-- Created by https://github.com/ekalinin/github-markdown-toc -->"
             local toc_footer
-            toc_footer="<!-- Added by: `whoami`, at: `date` -->"
+            toc_footer="<!-- Added by: $(whoami), at: $(date) -->"
             # http://fahdshariff.blogspot.ru/2012/12/sed-mutli-line-replacement-between-two.html
             # clear old TOC
             sed -i"${ext}" "/${ts}/,/${te}/{//!d;}" "$gh_src"
             # create toc file
-            echo "${toc}" > "${toc_path}"
+            echo "${toc}" >"${toc_path}"
             if [ "${no_footer}" != "yes" ]; then
-                echo -e "\n${toc_createdby}\n${toc_footer}\n" >> "$toc_path"
+                echo -e "\n${toc_createdby}\n${toc_footer}\n" >>"$toc_path"
             fi
 
             # insert toc file
-            if ! sed --version > /dev/null 2>&1; then
+            if ! sed --version || true >/dev/null 2>&1; then
                 sed -i "" "/${ts}/r ${toc_path}" "$gh_src"
             else
                 sed -i "/${ts}/r ${toc_path}" "$gh_src"
@@ -208,7 +224,7 @@ gh_toc(){
             if [ -z "${no_backup}" ]; then
                 echo "!! Origin version of the file: '${gh_src}${ext}'"
                 echo "!! TOC added into a separate file: '${toc_path}'"
-        fi
+            fi
             echo
         fi
     fi
@@ -243,7 +259,7 @@ gh_toc_grab() {
                     }
                     print sprintf("%*s", (level-1)*'"$2"', "") "* [" text "](" gh_url  modified_href ")"
                     '
-    if [ "`uname -s`" == "OS/390" ]; then
+    if [ "$(uname -s)" == "OS/390" ]; then
         grepcmd="pcregrep -o"
         echoargs=""
         awkscript='{
@@ -270,27 +286,27 @@ gh_toc_grab() {
     #   became: The command <code>foo1</code></h1>
     sed -e ':a' -e 'N' -e '$!ba' -e 's/\n<\/h/<\/h/g' |
 
-    # Sometimes a line can start with <span>. Fix that.
-    sed -e ':a' -e 'N' -e '$!ba' -e 's/\n<span/<span/g' |
+        # Sometimes a line can start with <span>. Fix that.
+        sed -e ':a' -e 'N' -e '$!ba' -e 's/\n<span/<span/g' |
 
-    # find strings that corresponds to template
-    $grepcmd '<h.*class="heading-element".*</a' |
+        # find strings that corresponds to template
+        $grepcmd '<h.*class="heading-element".*</a' |
 
-    # remove code tags
-    sed 's/<code>//g' | sed 's/<\/code>//g' |
+        # remove code tags
+        sed 's/<code>//g' | sed 's/<\/code>//g' |
 
-    # remove g-emoji
-    sed 's/<g-emoji[^>]*[^<]*<\/g-emoji> //g' |
+        # remove g-emoji
+        sed 's/<g-emoji[^>]*[^<]*<\/g-emoji> //g' |
 
-    # now all rows are like:
-    #   <h1 class="heading-element">title</h1><a href="..."><span>..</span></a>
-    # format result line
-    #   * $0 - whole string
-    #   * last element of each row: "</hN" where N in (1,2,3,...)
-    echo $echoargs "$(awk -v "gh_url=$1" "$awkscript")"
+        # now all rows are like:
+        #   <h1 class="heading-element">title</h1><a href="..."><span>..</span></a>
+        # format result line
+        #   * $0 - whole string
+        #   * last element of each row: "</hN" where N in (1,2,3,...)
+        echo $echoargs "$(awk -v "gh_url=$1" "$awkscript")"
 }
 
-        # perl -lpE 's/(\[[^\]]*\]\()(.*?)(\))/my ($pre, $in, $post)=($1, $2, $3) ; $in =~ s{\+}{ }g; $in =~ s{%}{\\x}g; $pre.$in.$post/ems')"
+# perl -lpE 's/(\[[^\]]*\]\()(.*?)(\))/my ($pre, $in, $post)=($1, $2, $3) ; $in =~ s{\+}{ }g; $in =~ s{%}{\\x}g; $pre.$in.$post/ems')"
 
 #
 # Returns filename only from full path or url
@@ -302,10 +318,10 @@ gh_toc_get_filename() {
 show_version() {
     echo "$gh_toc_version"
     echo
-    echo "os:     `uname -s`"
-    echo "arch:   `uname -m`"
-    echo "kernel: `uname -r`"
-    echo "shell:  `$SHELL --version`"
+    echo "os:     $(uname -s)"
+    echo "arch:   $(uname -m)"
+    echo "kernel: $(uname -r)"
+    echo "shell:  $($SHELL --version)"
     echo
     for tool in curl wget grep awk sed; do
         printf "%-5s: " $tool
@@ -346,7 +362,7 @@ gh_toc_app() {
     local need_replace="no"
     local indent=3
 
-    if [ "$1" = '--help' ] || [ $# -eq 0 ] ; then
+    if [ "$1" = '--help' ] || [ $# -eq 0 ]; then
         show_help
         return
     fi
@@ -368,7 +384,7 @@ gh_toc_app() {
             mkdir -p "$TMPDIR"
         fi
         local gh_tmp_md
-        if [ "`uname -s`" == "OS/390" ]; then
+        if [ "$(uname -s)" == "OS/390" ]; then
             local timestamp
             timestamp=$(date +%m%d%Y%H%M%S)
             gh_tmp_md="$TMPDIR/tmp.$timestamp"
@@ -376,7 +392,7 @@ gh_toc_app() {
             gh_tmp_md=$(mktemp "$TMPDIR/tmp.XXXXXX")
         fi
         while read -r input; do
-            echo "$input" >> "$gh_tmp_md"
+            echo "$input" >>"$gh_tmp_md"
         done
         gh_toc_md2html "$gh_tmp_md" | gh_toc_grab "" "$indent"
         return
@@ -404,9 +420,7 @@ gh_toc_app() {
         shift
     fi
 
-
-    for md in "$@"
-    do
+    for md in "$@"; do
         echo ""
         gh_toc "$md" "$#" "$need_replace" "$no_backup" "$no_footer" "$indent" "$skip_header"
     done