diff --git a/bb.sh b/bb.sh
index 0afc866..5b612dd 100755
--- a/bb.sh
+++ b/bb.sh
@@ -46,8 +46,6 @@ global_variables() {
 	# Set this to false for a Twitter button with share count. The cookieless version
 	# is just a link.
 	global_twitter_cookieless="true"
-	# Default search page, where tweets more than a week old are hidden
-	global_twitter_search="twitter"
 
 	# Blog generated files
 	# index page of blog (it is usually good to use "index.html" here)
@@ -152,7 +150,7 @@ global_variables() {
 
 	# Markdown location. Trying to autodetect by default.
 	# The invocation must support the signature 'markdown_bin in.md > out.html'
-	[[ -f Markdown.pl ]] && markdown_bin=./Markdown.pl || markdown_bin=$(which Markdown.pl 2>/dev/null || which markdown 2>/dev/null)
+	[[ -f Markdown.pl ]] && markdown_bin=./Markdown.pl || markdown_bin=$(command -v Markdown.pl 2>/dev/null || command -v markdown 2>/dev/null)
 }
 
 # Check for the validity of some variables
@@ -169,11 +167,12 @@ global_variables_check() {
 
 # Test if the markdown script is working correctly
 test_markdown() {
-	[[ -n $markdown_bin ]] &&
-		(
-		[[ $("$markdown_bin" <<< $'line 1\n\nline 2') == $'<p>line 1</p>\n\n<p>line 2</p>' ]] ||
-		[[ $("$markdown_bin" <<< $'line 1\n\nline 2') == $'<p>line 1</p>\n<p>line 2</p>' ]]
-		)
+	local m1; m1=$("$markdown_bin" <<< $'line 1\n\nline 2')
+	local m2; m2=$("$markdown_bin" <<< $'line 1\n\nline 2')
+	local c1=$'<p>line 1</p>\n\n<p>line 2</p>'
+	local c2=$'<p>line 1</p>\n<p>line 2</p>'
+	# shellcheck disable=SC2235 # must enforce order of operations
+	[[ -n $markdown_bin ]] && ( [[ "$m1" == "$c1" ]] || [[ "$m2" == "$c2" ]] )
 }
 
 
@@ -216,7 +215,8 @@ get_html_file_content() {
 #	"full" to edit full HTML, and not only text part (keeps old filename)
 #	leave empty for default behavior (edit only text part and change name)
 edit() {
-	[[ ! -f "${1%%.*}.html" ]] && echo "Can't edit post "${1%%.*}.html", did you mean to use \"bb.sh post <draft_file>\"?" && exit -1
+	[[ ! -f "${1%%.*}.html" ]] && \
+        printf "Can't edit post \"%s.html\", did you mean to use \"bb.sh post <draft_file>\"?\\n" "${1%%.*}" && exit 1
 	# Original post timestamp
 	edit_timestamp=$(LC_ALL=C date -r "${1%%.*}.html" +"$date_format_full" )
 	touch_timestamp=$(LC_ALL=C date -r "${1%%.*}.html" +"$date_format_timestamp")
@@ -226,8 +226,7 @@ edit() {
 		filename=$1
 	else
 		if [[ ${1##*.} == md ]]; then
-			test_markdown
-			if (($? != 0)); then
+			if test_markdown; then
 				echo "Markdown is not working, please edit HTML file directly."
 				exit
 			fi
@@ -260,7 +259,8 @@ edit() {
 	echo "Posted $filename"
 	tags_after=$(tags_in_post "$filename")
 	relevant_tags=$(echo "$tags_before $tags_after" | tr ',' ' ' | tr ' ' '\n' | sort -u | tr '\n' ' ')
-	if [[ ! -z $relevant_tags ]]; then
+	if [[ -n $relevant_tags ]]; then
+        # shellcheck disable=SC2086 # Intended splitting of $relevant_tags
 		relevant_posts="$(posts_with_tags $relevant_tags) $filename"
 		rebuild_tags "$relevant_posts" "$relevant_tags"
 	fi
@@ -324,7 +324,7 @@ is_boilerplate_file() {
 	done
 
 	case $name in
-	( "$index_file" | "$archive_index" | "$gophermap" | "$gemini_index" | "$tags_index" | "$footer_file" | "$header_file" | "$global_analytics_file" | "$prefix_tags"* )
+	( "$index_file" | "$archive_index" | "$gophermap" | "$gemini_index" | "$tags_index" | "$footer_file" | "$header_file" | "$prefix_tags"* )
 		return 0 ;;
 	( * ) # Check for excluded
 		for excl in "${html_exclude[@]}"; do
@@ -489,8 +489,7 @@ write_entry() {
 		[[ $2 == -html ]] && fmt=html
 		# Test if Markdown is working before re-posting a .md file
 		if [[ $extension == md ]]; then
-			test_markdown
-			if (($? != 0)); then
+			if test_markdown; then
 				echo "Markdown is not working, please edit HTML file directly."
 				exit
 			fi
@@ -560,6 +559,7 @@ EOF
 	echo "Posted $filename"
 	relevant_tags=$(tags_in_post $filename)
 	if [[ -n $relevant_tags ]]; then
+        # shellcheck disable=SC2086 # Intended splitting of $relevant_tags
 		relevant_posts="$(posts_with_tags $relevant_tags) $filename"
 		rebuild_tags "$relevant_posts" "$relevant_tags"
 	fi
@@ -616,6 +616,7 @@ all_tags() {
 	{
 		echo "<h3>$template_tags_title</h3>"
 		echo "<ul>"
+        # shellcheck disable=SC2231 # Intended splitting of $prefix_tags
 		for i in $prefix_tags*.html; do
 			[[ -f "$i" ]] || break
 			echo -n "." 1>&3
@@ -711,7 +712,8 @@ rebuild_tags() {
 		all_tags=yes
 	else
 		# will process only given files and tags
-		files=$(printf '%s\n' $1 | sort -u)
+		files=$(printf '%s\n' "$1" | sort -u)
+        # shellcheck disable=SC2086 # Intended splitting of $files
 		files=$(ls -t $files)
 		tags=$2
 	fi
@@ -773,10 +775,12 @@ get_post_author() {
 list_tags() {
 	if [[ $2 == -n ]]; then do_sort=1; else do_sort=0; fi
 
-	ls ./$prefix_tags*.html &> /dev/null
-	(($? != 0)) && echo "No posts yet. Use 'bb.sh post' to create one" && return
+	if ls ./$prefix_tags*.html > /dev/null; then
+		echo "No posts yet. Use 'bb.sh post' to create one" && return
+	fi
 
 	lines=""
+    # shellcheck disable=SC2231 # Intended splitting of $prefix_tags
 	for i in $prefix_tags*.html; do
 		[[ -f "$i" ]] || break
 		nposts=$(grep -c "<\!-- text begin -->" "$i")
@@ -796,8 +800,9 @@ list_tags() {
 
 # Displays a list of the posts
 list_posts() {
-	ls ./*.html &> /dev/null
-	(($? != 0)) && echo "No posts yet. Use 'bb.sh post' to create one" && return
+	if ls ./*.html > /dev/null; then
+		echo "No posts yet. Use 'bb.sh post' to create one" && return
+	fi
 
 	lines=""
 	n=1
@@ -864,7 +869,7 @@ make_gophermap() {
 	fi
 
 	if [ ! -f "${HOME}/public_gopher/blog/$gophermap" ]; then
-		cat <<- 'EOF' > $HOME/public_html/blog/$gophermap
+		cat <<- 'EOF' > "${HOME}/public_html/blog/${gophermap}"
 		#!/usr/bin/env sh
 		printf "my bashblog posts\n"
 		user=$(stat -c '%U' .)
@@ -873,9 +878,9 @@ make_gophermap() {
 			printf "0$post\t/~$user/blog/$post\ttilde.team\t70\n"
 		done
 		EOF
-		chmod +x $HOME/public_html/blog/$gophermap
+		chmod +x "${HOME}/public_html/blog/${gophermap}"
 	fi
-	chmod 644 *.md
+	chmod 644 ./*.md
 }
 
 make_gemini() {
@@ -889,7 +894,7 @@ make_gemini() {
 	fi
 
 	if [ ! -f "${HOME}/public_gemini/blog/$gemini_index" ]; then
-		cat <<- 'EOF' > $HOME/public_gemini/blog/$gemini_index
+		cat <<- 'EOF' > "${HOME}/public_gemini/blog/${gemini_index}"
 		#!/usr/bin/env sh
 		printf "20 text/gemini\r\n"
 		printf "my bashblog posts\r\n"
@@ -899,7 +904,7 @@ make_gemini() {
 			printf "=> /~$user/blog/$post $post\r\n"
 		done
 		EOF
-		chmod +x ${HOME}/public_gemini/blog/$gemini_index
+		chmod +x "${HOME}/public_gemini/blog/${gemini_index}"
 	fi
 }
 
@@ -1060,15 +1065,13 @@ reset() {
 
 # Detects if GNU date is installed
 date_version_detect() {
-	date --version >/dev/null 2>&1
-	if (($? != 0));  then
-		# date utility is BSD. Test if gdate is installed 
-		if gdate --version >/dev/null 2>&1 ; then
+	if ! stat -c"%U" /dev/null >/dev/null 2>&1 ; then
+		# BSD environment
+		if command -v gdate >/dev/null 2>&1 ; then
 			date() {
 				gdate "$@"
 			}
 		else
-			# BSD date
 			date() {
 				if [[ $1 == -r ]]; then
 					# Fall back to using stat for 'date -r'
@@ -1083,7 +1086,7 @@ date_version_detect() {
 				fi
 			}
 		fi
-	fi    
+	fi
 }
 
 # Main function
@@ -1093,14 +1096,16 @@ date_version_detect() {
 # $2     file name of a draft to continue editing (optional)
 do_main() {
 	# make sure we're in the right directory
-	[ $(pwd) != $HOME/public_html/blog ] &&
-		echo "you're not in your blog directory. moving you there now" && mkdir -p $HOME/public_html/blog && cd $HOME/public_html/blog
+	[ "$(pwd)" != "$HOME/public_html/blog" ] &&
+		echo "you're not in your blog directory. moving you there now" && \
+		mkdir -p "$HOME/public_html/blog" && cd "$HOME/public_html/blog" || exit 1
 
 	# Detect if using BSD date or GNU date
 	date_version_detect
 	# Load default configuration, then override settings with the config file
 	global_variables
-	[[ -f $global_config ]] && source "$global_config" &> /dev/null 
+	# shellcheck disable=SC1090 # variable config file
+	[[ -f "$global_config" ]] && source "$global_config" &> /dev/null 
 	global_variables_check
 
 	# Check for $EDITOR