diff --git a/todo.sh b/todo.sh
index a745ff5..66c3562 100755
--- a/todo.sh
+++ b/todo.sh
@@ -134,7 +134,7 @@ help()
 
 	EndOptionsHelp
 
-    [ $TODOTXT_VERBOSE -gt 1 ] && cat <<-'EndVerboseHelp'
+    [ "$TODOTXT_VERBOSE" -gt 1 ] && cat <<-'EndVerboseHelp'
 		  Environment variables:
 		    TODOTXT_AUTO_ARCHIVE            is same as option -a (0)/-A (1)
 		    TODOTXT_CFG_FILE=CONFIG_FILE    is same as option -d CONFIG_FILE
@@ -238,10 +238,10 @@ actionsHelp()
 		      Displays all the lines in SRC file located in the todo.txt directory,
 		      sorted by priority with line  numbers.  If TERM specified, lists
 		      all lines that contain TERM(s) in SRC file.  Hides all tasks that
-		      contain TERM(s) preceded by a minus sign (i.e. -TERM).  
+		      contain TERM(s) preceded by a minus sign (i.e. -TERM).
 		      Without any arguments, the names of all text files in the todo.txt
 		      directory are listed.
-		
+
 		    listpri [PRIORITIES] [TERM...]
 		    lsp [PRIORITIES] [TERM...]
 		      Displays all tasks prioritized PRIORITIES.
@@ -249,7 +249,7 @@ actionsHelp()
 		      If no PRIORITIES specified, lists all prioritized tasks.
 		      If TERM specified, lists only prioritized tasks that contain TERM(s).
 		      Hides all tasks that contain TERM(s) preceded by a minus sign
-		      (i.e. -TERM).  
+		      (i.e. -TERM).
 
 		    listproj [TERM...]
 		    lsprj [TERM...]
@@ -293,7 +293,7 @@ addonHelp()
         didPrintAddonActionsHeader=
         for action in "$TODO_ACTIONS_DIR"/*
         do
-            if [ -f "$action" -a -x "$action" ]; then
+            if [ -f "$action" ] && [ -x "$action" ]; then
                 if [ ! "$didPrintAddonActionsHeader" ]; then
                     cat <<-EndAddonActionsHeader
 		  Add-on Actions:
@@ -301,14 +301,14 @@ addonHelp()
                     didPrintAddonActionsHeader=1
                 fi
                 "$action" usage
-            elif [ -d "$action" -a -x "$action/$(basename $action)" ]; then
+            elif [ -d "$action" ] && [ -x "$action"/"$(basename "$action")" ]; then
                 if [ ! "$didPrintAddonActionsHeader" ]; then
                     cat <<-EndAddonActionsHeader
 		  Add-on Actions:
 	EndAddonActionsHeader
                     didPrintAddonActionsHeader=1
                 fi
-                "$action/$(basename $action)" usage
+                "$action"/"$(basename "$action")" usage
             fi
         done
     fi
@@ -319,10 +319,10 @@ actionUsage()
     for actionName
     do
         action="${TODO_ACTIONS_DIR}/${actionName}"
-        if [ -f "$action" -a -x "$action" ]; then
+        if [ -f "$action" ] && [ -x "$action" ]; then
             "$action" usage
-        elif [ -d "$action" -a -x "$action/$(basename $action)" ]; then
-            "$action/$(basename $action)" usage
+        elif [ -d "$action" ] && [ -x "$action"/"$(basename "$action")" ]; then
+            "$action"/"$(basename "$action")" usage
         else
             builtinActionUsage=$(actionsHelp | sed -n -e "/^    ${actionName//\//\\/} /,/^\$/p" -e "/^    ${actionName//\//\\/}$/,/^\$/p")
             if [ "$builtinActionUsage" ]; then
@@ -377,8 +377,9 @@ getPrefix()
     # Parameters:    $1: todo file; empty means $TODO_FILE.
     # Returns:       Uppercase FILE prefix to be used in place of "TODO:" where
     #                a different todo file can be specified.
-    local base=$(basename "${1:-$TODO_FILE}")
-    echo "${base%%.[^.]*}" | tr 'a-z' 'A-Z'
+    local base
+    base=$(basename "${1:-$TODO_FILE}")
+    echo "${base%%.[^.]*}" | tr '[:lower:]' '[:upper:]'
 }
 
 getTodo()
@@ -403,8 +404,8 @@ getNewtodo()
     # Postcondition: $newtodo contains task text.
 
     local item=$1
-    [ -z "$item" ] && die 'Programming error: $item should exist.'
-    [ "${item//[0-9]/}" ] && die 'Programming error: $item should be numeric.'
+    [ -z "$item" ] && die "Programming error: $item should exist."
+    [ "${item//[0-9]/}" ] && die "Programming error: $item should be numeric."
 
     newtodo=$(sed "$item!d" "${2:-$TODO_FILE}")
     [ -z "$newtodo" ] && die "$(getPrefix "$2"): No updated task $item."
@@ -428,7 +429,7 @@ replaceOrPrepend()
 
   if [[ -z "$1" && $TODOTXT_FORCE = 0 ]]; then
     echo -n "$querytext"
-    read -r -i $todo -e input
+    read -r -i "$todo" -e input
   else
     input=$*
   fi
@@ -438,7 +439,7 @@ replaceOrPrepend()
   priority=$(sed -e "$item!d" -e "${item}s/${priAndDateExpr}.*/\\1/" "$TODO_FILE")
   prepdate=$(sed -e "$item!d" -e "${item}s/${priAndDateExpr}.*/\\2/" "$TODO_FILE")
 
-  if [ "$prepdate" -a "$action" = "replace" ] && [ "$(echo "$input"|sed -e "s/${priAndDateExpr}.*/\\1\\2/")" ]; then
+  if [ "$prepdate" ] && [ "$action" = "replace" ] && [ "$(echo "$input"|sed -e "s/${priAndDateExpr}.*/\\1\\2/")" ]; then
       # If the replaced text starts with a [priority +] date, it will replace
       # the existing date, too.
     prepdate=
@@ -449,7 +450,7 @@ replaceOrPrepend()
   # date again.
   cleaninput "for sed"
   sed -i.bak -e "$item s/^${priority}${prepdate}//" -e "$item s|^.*|${priority}${prepdate}${input}${backref}|" "$TODO_FILE"
-  if [ $TODOTXT_VERBOSE -gt 0 ]; then
+  if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
     getNewtodo "$item"
     case "$action" in
       replace)
@@ -474,7 +475,7 @@ uppercasePriority()
     do
         upperPriority="${upperPriority};s/^[(]${lower[i]}[)]/(${upper[i]})/"
     done
-    input=$(echo "$input" | sed $upperPriority)
+    input=$(echo "$input" | sed "$upperPriority")
 }
 
 #Preserving environment variables so they don't get clobbered by the config file
@@ -491,20 +492,20 @@ OVR_TODOTXT_SORT_COMMAND="$TODOTXT_SORT_COMMAND"
 OVR_TODOTXT_FINAL_FILTER="$TODOTXT_FINAL_FILTER"
 
 # Prevent GREP_OPTIONS from malforming grep's output
-GREP_OPTIONS=""
+export GREP_OPTIONS=""
 
 # == PROCESS OPTIONS ==
 while getopts ":fhpcnNaAtTvVx+@Pd:" Option
 do
   case $Option in
-    '@' )
+    '@')
         ## HIDE_CONTEXT_NAMES starts at zero (false); increment it to one
         ##   (true) the first time this flag is seen. Each time the flag
         ##   is seen after that, increment it again so that an even
         ##   number shows context names and an odd number hides context
         ##   names.
         : $(( HIDE_CONTEXT_NAMES++ ))
-        if [ $(( $HIDE_CONTEXT_NAMES % 2 )) -eq 0 ]
+        if [ $(( HIDE_CONTEXT_NAMES % 2 )) -eq 0 ]
         then
             ## Zero or even value -- show context names
             unset HIDE_CONTEXTS_SUBSTITUTION
@@ -513,14 +514,14 @@ do
             export HIDE_CONTEXTS_SUBSTITUTION='[[:space:]]@[[:graph:]]\{1,\}'
         fi
         ;;
-    '+' )
+    '+')
         ## HIDE_PROJECT_NAMES starts at zero (false); increment it to one
         ##   (true) the first time this flag is seen. Each time the flag
         ##   is seen after that, increment it again so that an even
         ##   number shows project names and an odd number hides project
         ##   names.
         : $(( HIDE_PROJECT_NAMES++ ))
-        if [ $(( $HIDE_PROJECT_NAMES % 2 )) -eq 0 ]
+        if [ $(( HIDE_PROJECT_NAMES % 2 )) -eq 0 ]
         then
             ## Zero or even value -- show project names
             unset HIDE_PROJECTS_SUBSTITUTION
@@ -529,45 +530,45 @@ do
             export HIDE_PROJECTS_SUBSTITUTION='[[:space:]][+][[:graph:]]\{1,\}'
         fi
         ;;
-    a )
+    a)
         OVR_TODOTXT_AUTO_ARCHIVE=0
         ;;
-    A )
+    A)
         OVR_TODOTXT_AUTO_ARCHIVE=1
         ;;
-    c )
+    c)
         OVR_TODOTXT_PLAIN=0
         ;;
-    d )
+    d)
         TODOTXT_CFG_FILE=$OPTARG
         ;;
-    f )
+    f)
         OVR_TODOTXT_FORCE=1
         ;;
-    h )
+    h)
         # Short-circuit option parsing and forward to the action.
         # Cannot just invoke shorthelp() because we need the configuration
         # processed to locate the add-on actions directory.
         set -- '-h' 'shorthelp'
         OPTIND=2
         ;;
-    n )
+    n)
         OVR_TODOTXT_PRESERVE_LINE_NUMBERS=0
         ;;
-    N )
+    N)
         OVR_TODOTXT_PRESERVE_LINE_NUMBERS=1
         ;;
-    p )
+    p)
         OVR_TODOTXT_PLAIN=1
         ;;
-    P )
+    P)
         ## HIDE_PRIORITY_LABELS starts at zero (false); increment it to one
         ##   (true) the first time this flag is seen. Each time the flag
         ##   is seen after that, increment it again so that an even
         ##   number shows priority labels and an odd number hides priority
         ##   labels.
         : $(( HIDE_PRIORITY_LABELS++ ))
-        if [ $(( $HIDE_PRIORITY_LABELS % 2 )) -eq 0 ]
+        if [ $(( HIDE_PRIORITY_LABELS % 2 )) -eq 0 ]
         then
             ## Zero or even value -- show priority labels
             unset HIDE_PRIORITY_SUBSTITUTION
@@ -576,24 +577,27 @@ do
             export HIDE_PRIORITY_SUBSTITUTION="([A-Z])[[:space:]]"
         fi
         ;;
-    t )
+    t)
         OVR_TODOTXT_DATE_ON_ADD=1
         ;;
-    T )
+    T)
         OVR_TODOTXT_DATE_ON_ADD=0
         ;;
-    v )
+    v)
         : $(( TODOTXT_VERBOSE++ ))
         ;;
-    V )
+    V)
         version
         ;;
-    x )
+    x)
         OVR_TODOTXT_DISABLE_FILTER=1
         ;;
+    *)
+        usage
+        ;;
   esac
 done
-shift $(($OPTIND - 1))
+shift $((OPTIND - 1))
 
 # defaults if not yet defined
 TODOTXT_VERBOSE=${TODOTXT_VERBOSE:-1}
@@ -611,7 +615,7 @@ TODOTXT_FINAL_FILTER=${TODOTXT_FINAL_FILTER:-cat}
 TODOTXT_GLOBAL_CFG_FILE=${TODOTXT_GLOBAL_CFG_FILE:-/etc/todo/config}
 
 # Export all TODOTXT_* variables
-export ${!TODOTXT_@}
+export "${!TODOTXT_@}"
 
 # Default color map
 export NONE=''
@@ -698,7 +702,7 @@ export SENTENCE_DELIMITERS=',.:;'
 }
 
 
-if [ -z "$TODO_ACTIONS_DIR" -o ! -d "$TODO_ACTIONS_DIR" ]
+if [ -z "$TODO_ACTIONS_DIR" ] || [ ! -d "$TODO_ACTIONS_DIR" ]
 then
     TODO_ACTIONS_DIR="$HOME/.todo/actions"
     export TODO_ACTIONS_DIR
@@ -765,19 +769,19 @@ fi
 ACTION=${1:-$TODOTXT_DEFAULT_ACTION}
 
 [ -z "$ACTION" ]    && usage
-[ -d "$TODO_DIR" ]  || mkdir -p $TODO_DIR 2> /dev/null || dieWithHelp "$1" "Fatal Error: $TODO_DIR is not a directory"
+[ -d "$TODO_DIR" ]  || mkdir -p "$TODO_DIR" 2> /dev/null || dieWithHelp "$1" "Fatal Error: $TODO_DIR is not a directory"
 ( cd "$TODO_DIR" )  || dieWithHelp "$1" "Fatal Error: Unable to cd to $TODO_DIR"
 [ -z "$TODOTXT_PRIORITY_ON_ADD" ] \
     || echo "$TODOTXT_PRIORITY_ON_ADD" | grep -q "^[A-Z]$" \
     || die "TODOTXT_PRIORITY_ON_ADD should be a capital letter from A to Z (it is now \"$TODOTXT_PRIORITY_ON_ADD\")."
 
-[ -f "$TODO_FILE" -o -c "$TODO_FILE" ] || > "$TODO_FILE"
-[ -f "$DONE_FILE" -o -c "$DONE_FILE" ] || > "$DONE_FILE"
-[ -f "$REPORT_FILE" -o -c "$REPORT_FILE" ] || > "$REPORT_FILE"
+[ -f "$TODO_FILE" ] || [ -c "$TODO_FILE" ] || > "$TODO_FILE"
+[ -f "$DONE_FILE" ] || [ -c "$DONE_FILE" ] || > "$DONE_FILE"
+[ -f "$REPORT_FILE" ] || [ -c "$REPORT_FILE" ] || > "$REPORT_FILE"
 
 if [ $TODOTXT_PLAIN = 1 ]; then
     for clr in ${!PRI_@}; do
-        export $clr=$NONE
+        export "$clr"=$NONE
     done
     PRI_X=$NONE
     DEFAULT=$NONE
@@ -795,7 +799,7 @@ _addto() {
     cleaninput
     uppercasePriority
 
-    if [[ $TODOTXT_DATE_ON_ADD = 1 ]]; then
+    if [[ "$TODOTXT_DATE_ON_ADD" -eq 1 ]]; then
         now=$(date '+%Y-%m-%d')
         input=$(echo "$input" | sed -e 's/^\(([A-Z]) \)\{0,1\}/\1'"$now /")
     fi
@@ -805,7 +809,7 @@ _addto() {
         fi
     fi
     echo "$input" >> "$file"
-    if [ $TODOTXT_VERBOSE -gt 0 ]; then
+    if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
         TASKNUM=$(sed -n '$ =' "$file")
         echo "$TASKNUM $input"
         echo "$(getPrefix "$file"): $TASKNUM added."
@@ -873,7 +877,7 @@ _list() {
 
     _format "$src" '' "$@"
 
-    if [ $TODOTXT_VERBOSE -gt 0 ]; then
+    if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
         echo "--"
         echo "$(getPrefix "$src"): ${NUMTASKS:-0} of ${TOTALTASKS:-0} tasks shown"
     fi
@@ -933,7 +937,7 @@ _format()
             s/^  /00/;
             s/^ /0/;
           ''' \
-        | eval ${TODOTXT_SORT_COMMAND}                                        \
+        | eval "${TODOTXT_SORT_COMMAND}" \
         | awk '''
             function highlight(colorVar,      color) {
                 color = ENVIRON[colorVar]
@@ -984,11 +988,11 @@ _format()
     )
     [ "$filtered_items" ] && echo "$filtered_items"
 
-    if [ $TODOTXT_VERBOSE -gt 0 ]; then
+    if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
         NUMTASKS=$( echo -n "$filtered_items" | sed -n '$ =' )
         TOTALTASKS=$( echo -n "$items" | sed -n '$ =' )
     fi
-    if [ $TODOTXT_VERBOSE -gt 1 ]; then
+    if [ "$TODOTXT_VERBOSE" -gt 1 ]; then
         echo "TODO DEBUG: Filter Command was: ${filter_command:-cat}"
     fi
 }
@@ -1006,7 +1010,7 @@ listWordsWithSigil()
 export -f cleaninput getPrefix getTodo getNewtodo shellquote filtercommand _list listWordsWithSigil getPadding _format die
 
 # == HANDLE ACTION ==
-action=$( printf "%s\n" "$ACTION" | tr 'A-Z' 'a-z' )
+action=$( printf "%s\n" "$ACTION" | tr '[:upper:]' '[:lower:]' )
 
 ## If the first argument is "command", run the rest of the arguments
 ## using todo.sh builtins.
@@ -1017,12 +1021,12 @@ then
     ## Get rid of "command" from arguments list
     shift
     ## Reset action to new first argument
-    action=$( printf "%s\n" "$1" | tr 'A-Z' 'a-z' )
-elif [ -d "$TODO_ACTIONS_DIR/$action" -a -x "$TODO_ACTIONS_DIR/$action/$action" ]
+    action=$( printf "%s\n" "$1" | tr '[:upper:]' '[:lower:]' )
+elif [ -d "$TODO_ACTIONS_DIR/$action" ] && [ -x "$TODO_ACTIONS_DIR/$action/$action" ]
 then
     "$TODO_ACTIONS_DIR/$action/$action" "$@"
     exit $?
-elif [ -d "$TODO_ACTIONS_DIR" -a -x "$TODO_ACTIONS_DIR/$action" ]
+elif [ -d "$TODO_ACTIONS_DIR" ] && [ -x "$TODO_ACTIONS_DIR/$action" ]
 then
     "$TODO_ACTIONS_DIR/$action" "$@"
     exit $?
@@ -1052,7 +1056,7 @@ case $action in
         input=$*
     fi
 
-    # Set Internal Field Seperator as newline so we can 
+    # Set Internal Field Seperator as newline so we can
     # loop across multiple lines
     SAVEIFS=$IFS
     IFS=$'\n'
@@ -1096,8 +1100,8 @@ case $action in
     esac
     cleaninput "for sed"
 
-    if sed -i.bak $item" s|^.*|&${appendspace}${input}|" "$TODO_FILE"; then
-        if [ $TODOTXT_VERBOSE -gt 0 ]; then
+    if sed -i.bak "${item} s|^.*|&${appendspace}${input}|" "$TODO_FILE"; then
+        if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
             getNewtodo "$item"
             echo "$item $newtodo"
 	fi
@@ -1109,10 +1113,10 @@ case $action in
 "archive" )
     # defragment blank lines
     sed -i.bak -e '/./!d' "$TODO_FILE"
-    [ $TODOTXT_VERBOSE -gt 0 ] && grep "^x " "$TODO_FILE"
+    [ "$TODOTXT_VERBOSE" -gt 0 ] && grep "^x " "$TODO_FILE"
     grep "^x " "$TODO_FILE" >> "$DONE_FILE"
     sed -i.bak '/^x /d' "$TODO_FILE"
-    if [ $TODOTXT_VERBOSE -gt 0 ]; then
+    if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
 	echo "TODO: $TODO_FILE archived."
     fi
     ;;
@@ -1133,12 +1137,12 @@ case $action in
         if [ "$ANSWER" = "y" ]; then
             if [ $TODOTXT_PRESERVE_LINE_NUMBERS = 0 ]; then
                 # delete line (changes line numbers)
-                sed -i.bak -e $item"s/^.*//" -e '/./!d' "$TODO_FILE"
+                sed -i.bak -e "${item}s/^.*//" -e '/./!d' "$TODO_FILE"
             else
                 # leave blank line behind (preserves line numbers)
-                sed -i.bak -e $item"s/^.*//" "$TODO_FILE"
+                sed -i.bak -e "${item}s/^.*//" "$TODO_FILE"
             fi
-            if [ $TODOTXT_VERBOSE -gt 0 ]; then
+            if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
                 echo "$item $todo"
                 echo "TODO: $item deleted."
             fi
@@ -1147,18 +1151,18 @@ case $action in
         fi
     else
         sed -i.bak \
-            -e $item"s/^\((.) \)\{0,1\} *$3 */\1/g" \
-            -e $item"s/ *$3 *\$//g" \
-            -e $item"s/  *$3 */ /g" \
-            -e $item"s/ *$3  */ /g" \
-            -e $item"s/$3//g" \
+            -e "${item}s/^\((.) \)\{0,1\} *$3 */\1/g" \
+            -e "${item}s/ *$3 *\$//g" \
+            -e "${item}s/  *$3 */ /g" \
+            -e "${item}s/ *$3  */ /g" \
+            -e "${item}s/$3//g" \
             "$TODO_FILE"
         getNewtodo "$item"
         if [ "$todo" = "$newtodo" ]; then
-            [ $TODOTXT_VERBOSE -gt 0 ] && echo "$item $todo"
+            [ "$TODOTXT_VERBOSE" -gt 0 ] && echo "$item $todo"
             die "TODO: '$3' not found; no removal done."
         fi
-        if [ $TODOTXT_VERBOSE -gt 0 ]; then
+        if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
             echo "$item $todo"
             echo "TODO: Removed '$3' from task."
             echo "$item $newtodo"
@@ -1177,8 +1181,8 @@ case $action in
         getTodo "$item"
 
 	if [[ "$todo" = \(?\)\ * ]]; then
-	    sed -i.bak -e $item"s/^(.) //" "$TODO_FILE"
-	    if [ $TODOTXT_VERBOSE -gt 0 ]; then
+	    sed -i.bak -e "${item}s/^(.) //" "$TODO_FILE"
+	    if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
 		getNewtodo "$item"
 		echo "$item $newtodo"
 		echo "TODO: $item deprioritized."
@@ -1204,9 +1208,9 @@ case $action in
         if [ "${todo:0:2}" != "x " ]; then
             now=$(date '+%Y-%m-%d')
             # remove priority once item is done
-            sed -i.bak $item"s/^(.) //" "$TODO_FILE"
-            sed -i.bak $item"s|^|x $now |" "$TODO_FILE"
-            if [ $TODOTXT_VERBOSE -gt 0 ]; then
+            sed -i.bak "${item}s/^(.) //" "$TODO_FILE"
+            sed -i.bak "${item}s|^|x $now |" "$TODO_FILE"
+            if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
                 getNewtodo "$item"
                 echo "$item $newtodo"
                 echo "TODO: $item marked as done."
@@ -1263,7 +1267,7 @@ case $action in
     post_filter_command="${post_filter_command:-}${post_filter_command:+ | }awk -v TOTAL=$TOTAL -v PADDING=$PADDING '{ \$1 = sprintf(\"%\" PADDING \"d\", (\$1 > TOTAL ? 0 : \$1)); print }' "
     cat "$TODO_FILE" "$DONE_FILE" | TODOTXT_VERBOSE=0 _format '' "$PADDING" "$@"
 
-    if [ $TODOTXT_VERBOSE -gt 0 ]; then
+    if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
         TDONE=$( sed -n '$ =' "$DONE_FILE" )
         TASKNUM=$(TODOTXT_PLAIN=1 TODOTXT_VERBOSE=0 _format "$TODO_FILE" 1 "$@" | sed -n '$ =')
         DONENUM=$(TODOTXT_PLAIN=1 TODOTXT_VERBOSE=0 _format "$DONE_FILE" 1 "$@" | sed -n '$ =')
@@ -1277,8 +1281,8 @@ case $action in
 "listfile" | "lf" )
     shift  ## Was listfile, next $1 is file name
     if [ $# -eq 0 ]; then
-        [ $TODOTXT_VERBOSE -gt 0 ] && echo "Files in the todo.txt directory:"
-        cd "$TODO_DIR" && ls -1 *.txt
+        [ "$TODOTXT_VERBOSE" -gt 0 ] && echo "Files in the todo.txt directory:"
+        cd "$TODO_DIR" && ls -1 -- *.txt
     else
         FILE="$1"
         shift  ## Was filename; next $1 is first search term
@@ -1300,7 +1304,7 @@ case $action in
 "listpri" | "lsp" )
     shift ## was "listpri", new $1 is priority to list or first TERM
 
-    pri=$(printf "%s\n" "$1" | tr 'a-z' 'A-Z' | grep -e '^[A-Z]$' -e '^[A-Z]-[A-Z]$') && shift || pri="A-Z"
+    pri=$(printf "%s\n" "$1" | tr '[:lower:]' '[:upper:]' | grep -e '^[A-Z]$' -e '^[A-Z]-[A-Z]$') && shift || pri="A-Z"
     post_filter_command="${post_filter_command:-}${post_filter_command:+ | }grep '^ *[0-9]\+ ([${pri}]) '"
     _list "$TODO_FILE" "$@"
     ;;
@@ -1329,14 +1333,14 @@ case $action in
     if [ "$ANSWER" = "y" ]; then
         if [ $TODOTXT_PRESERVE_LINE_NUMBERS = 0 ]; then
             # delete line (changes line numbers)
-            sed -i.bak -e $item"s/^.*//" -e '/./!d' "$src"
+            sed -i.bak -e "${item}s/^.*//" -e '/./!d' "$src"
         else
             # leave blank line behind (preserves line numbers)
-            sed -i.bak -e $item"s/^.*//" "$src"
+            sed -i.bak -e "${item}s/^.*//" "$src"
         fi
         echo "$todo" >> "$dest"
 
-        if [ $TODOTXT_VERBOSE -gt 0 ]; then
+        if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
             echo "$item $todo"
             echo "TODO: $item moved from '$src' to '$dest'."
         fi
@@ -1352,7 +1356,7 @@ case $action in
 
 "pri" | "p" )
     item=$2
-    newpri=$( printf "%s\n" "$3" | tr 'a-z' 'A-Z' )
+    newpri=$( printf "%s\n" "$3" | tr '[:lower:]' '[:upper:]' )
 
     errmsg="usage: $TODO_SH pri ITEM# PRIORITY
 note: PRIORITY must be anywhere from A to Z."
@@ -1367,9 +1371,9 @@ note: PRIORITY must be anywhere from A to Z."
     fi
 
     if [ "$oldpri" != "$newpri" ]; then
-        sed -i.bak -e $item"s/^(.) //" -e $item"s/^/($newpri) /" "$TODO_FILE"
+        sed -i.bak -e "${item}s/^(.) //" -e "${item}s/^/($newpri) /" "$TODO_FILE"
     fi
-    if [ $TODOTXT_VERBOSE -gt 0 ]; then
+    if [ "$TODOTXT_VERBOSE" -gt 0 ]; then
         getNewtodo "$item"
         echo "$item $newtodo"
         if [ "$oldpri" != "$newpri" ]; then
@@ -1403,12 +1407,12 @@ note: PRIORITY must be anywhere from A to Z."
     LASTDATA=${LASTREPORT#* }   # Strip timestamp.
     if [ "$LASTDATA" = "$NEWDATA" ]; then
         echo "$LASTREPORT"
-        [ $TODOTXT_VERBOSE -gt 0 ] && echo "TODO: Report file is up-to-date."
+        [ "$TODOTXT_VERBOSE" -gt 0 ] && echo "TODO: Report file is up-to-date."
     else
         NEWREPORT="$(date +%Y-%m-%dT%T) ${NEWDATA}"
         echo "${NEWREPORT}" >> "$REPORT_FILE"
         echo "${NEWREPORT}"
-        [ $TODOTXT_VERBOSE -gt 0 ] && echo "TODO: Report file updated."
+        [ "$TODOTXT_VERBOSE" -gt 0 ] && echo "TODO: Report file updated."
     fi
     ;;
 
@@ -1461,9 +1465,9 @@ note: PRIORITY must be anywhere from A to Z."
         cd "$TODO_ACTIONS_DIR" || exit $?
         for action in *
         do
-            if [ -f "$action" -a -x "$action" ]; then
+            if [ -f "$action" ] && [ -x "$action" ]; then
                 echo "$action"
-            elif [ -d "$action" -a -x "$action/$action" ]; then
+            elif [ -d "$action" ] && [ -x "$action/$action" ]; then
                 echo "$action"
             fi
         done