diff --git a/.shellcheckrc b/.shellcheckrc
index 58675d59d2b..3a3d9395d30 100644
--- a/.shellcheckrc
+++ b/.shellcheckrc
@@ -5,6 +5,7 @@ disable=SC1090  # not really fixable usually (ever?)
 disable=SC2034  # for localizing variables set in called functions
 disable=SC2128  # intentional style choice
 disable=SC2206  # suggested alternatives fail in posix mode or use temp files
+disable=SC2209  # interferes with our `set` (literal) vs empty booleans
 disable=SC2207  # suggested alternatives fail in posix mode or use temp files
 
 # These disables are to be investigated and decided
diff --git a/bash_completion b/bash_completion
index 1bfab05d8d5..6e297dc756f 100644
--- a/bash_completion
+++ b/bash_completion
@@ -339,12 +339,12 @@ _comp_expand_glob()
 #   generated.
 _comp_split()
 {
-    local _append=false IFS=$' \t\n'
+    local _append="" IFS=$' \t\n'
 
     local OPTIND=1 OPTARG="" OPTERR=0 _opt
     while getopts ':alF:' _opt "$@"; do
         case $_opt in
-            a) _append=true ;;
+            a) _append=set ;;
             l) IFS=$'\n' ;;
             F) IFS=$OPTARG ;;
             *)
@@ -367,7 +367,7 @@ _comp_split()
     set -o noglob
 
     local _old_size _new_size
-    if "$_append"; then
+    if [[ $_append ]]; then
         eval "$1+=()" # in case $1 is unset
         eval "_old_size=\${#$1[@]}"
         eval "$1+=(\$2)"
@@ -409,13 +409,13 @@ _comp_split()
 #   array instead.
 _comp_compgen()
 {
-    local _append=false IFS=$' \t\n'
+    local _append="" IFS=$' \t\n'
     local -a _split_options=(-l)
 
     local OPTIND=1 OPTARG="" OPTERR=0 _opt
     while getopts ':alF:' _opt "$@"; do
         case $_opt in
-            a) _append=true _split_options+=(-a) ;;
+            a) _append=set _split_options+=(-a) ;;
             l) IFS=$'\n' ;;
             F) IFS=$OPTARG ;;
             *)
@@ -447,7 +447,7 @@ _comp_compgen()
     local _result
     _result=$(compgen "${@:2}") || {
         local _status=$?
-        if "$_append"; then
+        if [[ $_append ]]; then
             # make sure existence of variable
             eval -- "$1+=()"
         else
@@ -859,16 +859,16 @@ _variables()
 #         -k: do not filter out already present tokens in value
 _comp_delimited()
 {
-    local prefix="" delimiter=$1 deduplicate=true
+    local prefix="" delimiter=$1 deduplicate=set
     shift
     if [[ $delimiter == -k ]]; then
-        deduplicate=false
+        deduplicate=""
         delimiter=$1
         shift
     fi
     [[ $cur == *$delimiter* ]] && prefix=${cur%"$delimiter"*}$delimiter
 
-    if $deduplicate; then
+    if [[ $deduplicate ]]; then
         # We could construct a -X pattern to feed to compgen, but that'd
         # conflict with possibly already set -X in $@, as well as have
         # glob char escaping issues to deal with. Do removals by hand instead.
@@ -1959,7 +1959,7 @@ _known_hosts_real()
     local OPTIND=1
     while getopts "ac46F:p:" flag "$@"; do
         case $flag in
-            a) aliases='yes' ;;
+            a) aliases=set ;;
             c) suffix=':' ;;
             F)
                 if [[ ! $OPTARG ]]; then
@@ -1969,8 +1969,8 @@ _known_hosts_real()
                 configfile=$OPTARG
                 ;;
             p) prefix=$OPTARG ;;
-            4) ipv4=1 ;;
-            6) ipv6=1 ;;
+            4) ipv4=set ;;
+            6) ipv6=set ;;
             *)
                 echo "bash_completion: $FUNCNAME: usage error" >&2
                 return 1
diff --git a/completions/_adb b/completions/_adb
index ed11dad0697..d1e3a8af5c6 100644
--- a/completions/_adb
+++ b/completions/_adb
@@ -25,16 +25,16 @@ _comp_cmd_adb()
             ;;
     esac
 
-    local cmd has_cmd=false i
+    local cmd has_cmd="" i
     for ((i = 1; i < cword; i++)); do
         if [[ ${words[i]} != -* && ${words[i - 1]} != -[sp] ]]; then
             cmd="${words[i]}"
-            has_cmd=true
+            has_cmd=set
             break
         fi
     done
 
-    if ! "$has_cmd"; then
+    if [[ ! $has_cmd ]]; then
         local tmp=()
         if [[ ! $cur || $cur == -* ]]; then
             tmp+=($(compgen -W '$(_parse_help "$1" help)' -- "$cur"))
diff --git a/completions/_chsh b/completions/_chsh
index b6569ce7af6..651a5a660b1 100644
--- a/completions/_chsh
+++ b/completions/_chsh
@@ -8,13 +8,13 @@ _comp_cmd_chsh()
     local cur prev words cword comp_args
     _comp_initialize -- "$@" || return
 
-    local word chroot="" has_chroot=false
+    local word chroot="" has_chroot=""
     for word in "${words[@]}"; do
-        if "$has_chroot"; then
+        if [[ $has_chroot ]]; then
             chroot=$word
             break
         fi
-        [[ $word != -@(R|-root) ]] || has_chroot=true
+        [[ $word != -@(R|-root) ]] || has_chroot=set
     done
 
     case $prev in
diff --git a/completions/_mount.linux b/completions/_mount.linux
index 91a543120fa..ac41ae68f1d 100644
--- a/completions/_mount.linux
+++ b/completions/_mount.linux
@@ -8,7 +8,7 @@ _comp_cmd_mount()
     local cur prev words cword comp_args
     _comp_initialize -n =: -- "$@" || return
 
-    local split=false
+    local split=""
     case "$prev" in
         -t | --types)
             # find /lib/modules/$(uname -r)/ -type f -path '*/fs/*.ko' -printf '%f\n' | cut -d. -f1
@@ -16,7 +16,7 @@ _comp_cmd_mount()
             if [[ $cur == ?*,* ]]; then
                 prev="${cur%,*}"
                 cur="${cur##*,}"
-                split=true
+                split=set
             fi
             COMPREPLY=($(compgen -W 'auto adfs affs autofs btrfs cifs coda
                 cramfs davfs debugfs devpts efs ext2 ext3 ext4 fuse hfs hfsplus
@@ -24,7 +24,7 @@ _comp_cmd_mount()
                 proc qnx4 ramfs reiserfs romfs squashfs smbfs sysv tmpfs ubifs
                 udf ufs umsdos usbfs vfat xfs' -- "$cur"))
             _fstypes
-            $split && COMPREPLY=(${COMPREPLY[@]/#/$prev,})
+            [[ $split ]] && COMPREPLY=(${COMPREPLY[@]/#/$prev,})
             return
             ;;
         --bind | -B | --rbind | -R)
@@ -74,7 +74,7 @@ _comp_cmd_mount()
             if [[ $cur == ?*,* ]]; then
                 prev="${cur%,*}"
                 cur="${cur##*,}"
-                split=true
+                split=set
             fi
             # no completion if $cur is opt=smth
             [[ $cur == *=* ]] && return
@@ -206,7 +206,7 @@ _comp_cmd_mount()
             esac
             # COMP_WORDBREAKS is a real pain in the ass
             prev="${prev##*["$COMP_WORDBREAKS"]}"
-            $split && COMPREPLY=(${COMPREPLY[@]/#/"$prev,"})
+            [[ $split ]] && COMPREPLY=(${COMPREPLY[@]/#/"$prev,"})
             [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
             return
             ;;
diff --git a/completions/_slackpkg b/completions/_slackpkg
index 153d4a10fbc..7e234d4e6ba 100644
--- a/completions/_slackpkg
+++ b/completions/_slackpkg
@@ -9,11 +9,11 @@ _comp_cmd_slackpkg()
     local cur prev words cword comp_args
     _comp_initialize -n = -- "$@" || return
 
-    local split=false
+    local split=""
     if [[ $cur == -?*=* ]]; then
         prev="${cur%%?(\\)=*}"
         cur="${cur#*=}"
-        split=true
+        split=set
     fi
 
     case "$prev" in
@@ -33,7 +33,7 @@ _comp_cmd_slackpkg()
             ;;
     esac
 
-    $split && return
+    [[ $split ]] && return
 
     if [[ $cur == -* ]]; then
         compopt -o nospace
diff --git a/completions/_udevadm b/completions/_udevadm
index 5332989632f..2735627a6b0 100644
--- a/completions/_udevadm
+++ b/completions/_udevadm
@@ -8,11 +8,11 @@ _comp_cmd_udevadm()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local i udevcmd has_udevcmd=false
+    local i udevcmd has_udevcmd=""
     for ((i = 1; i < cword; i++)); do
         if [[ ${words[i]} != -* ]]; then
             udevcmd=${words[i]}
-            has_udevcmd=true
+            has_udevcmd=set
             break
         fi
     done
@@ -54,7 +54,7 @@ _comp_cmd_udevadm()
 
     $split && return
 
-    if ! "$has_udevcmd"; then
+    if [[ ! $has_udevcmd ]]; then
         case $cur in
             -*)
                 COMPREPLY=($(compgen -W '--help --version --debug' -- "$cur"))
diff --git a/completions/_umount.linux b/completions/_umount.linux
index 609de7d4bc3..321df9504c3 100644
--- a/completions/_umount.linux
+++ b/completions/_umount.linux
@@ -101,11 +101,11 @@ _comp_cmd_umount()
     case "$prev" in
         -t)
             # FIXME: no<fstype>
-            local split=false
+            local split=""
             if [[ $cur == ?*,* ]]; then
                 prev="${cur%,*}"
                 cur="${cur##*,}"
-                split=true
+                split=set
             fi
             COMPREPLY=($(compgen -W 'adfs affs autofs btrfs cifs coda
                 cramfs debugfs devpts efs ext2 ext3 ext4 fuse hfs hfsplus hpfs
@@ -113,7 +113,7 @@ _comp_cmd_umount()
                 ramfs reiserfs romfs squashfs smbfs sysv tmpfs ubifs udf ufs
                 umsdos usbfs vfat xfs' -- "$cur"))
             _fstypes
-            $split && COMPREPLY=(${COMPREPLY[@]/#/$prev,})
+            [[ $split ]] && COMPREPLY=(${COMPREPLY[@]/#/$prev,})
             return
             ;;
         -O)
diff --git a/completions/carton b/completions/carton
index 5953bc9309c..f79ed2b7a88 100644
--- a/completions/carton
+++ b/completions/carton
@@ -18,19 +18,19 @@ _carton()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local i command="" has_command=false
+    local i command="" has_command=""
     for ((i = 1; i < cword; i++)); do
         case ${words[i]} in
             -*) ;;
             *)
                 command=${words[i]}
-                has_command=true
+                has_command=set
                 break
                 ;;
         esac
     done
 
-    if ! "$has_command"; then
+    if [[ ! $has_command ]]; then
         _carton_commands "$1"
         return
     fi
@@ -40,7 +40,7 @@ _carton()
             return
             ;;
         --help | -h)
-            "$has_command" || _carton_commands "$1"
+            [[ $has_command ]] || _carton_commands "$1"
             return
             ;;
         --cpanfile)
diff --git a/completions/cvs b/completions/cvs
index b8f19bb6043..66ff9b6fe41 100644
--- a/completions/cvs
+++ b/completions/cvs
@@ -53,7 +53,7 @@ _cvs()
     local cur prev words cword comp_args
     _comp_initialize -n : -- "$@" || return
 
-    local count mode="" i cvsroot="" has_cvsroot=false cvsroots pwd
+    local count mode="" i cvsroot="" has_cvsroot="" cvsroots pwd
     local -a flags files entries changed newremoved
 
     local noargopts='!(-*|*[d]*)'
@@ -74,7 +74,7 @@ _cvs()
                 -${noargopts}d)
                     mode=cvsroot
                     cvsroot=${words[count + 1]}
-                    has_cvsroot=true
+                    has_cvsroot=set
                     ;;
                 add | ad | new)
                     mode=add
@@ -232,7 +232,7 @@ _cvs()
             esac
 
             if [[ $cur != -* ]]; then
-                ! "$has_cvsroot" && cvsroot=${CVSROOT-}
+                [[ ! $has_cvsroot ]] && cvsroot=${CVSROOT-}
                 COMPREPLY=($(cvs -d "$cvsroot" co -c 2>/dev/null |
                     awk '{print $1}'))
                 ((${#COMPREPLY[@]})) &&
@@ -317,7 +317,7 @@ _cvs()
             esac
 
             if [[ $cur != -* ]]; then
-                ! "$has_cvsroot" && cvsroot=${CVSROOT-}
+                [[ ! $has_cvsroot ]] && cvsroot=${CVSROOT-}
                 COMPREPLY=($(cvs -d "$cvsroot" co -c | awk '{print $1}'))
                 ((${#COMPREPLY[@]})) &&
                     COMPREPLY=($(compgen -W '"${COMPREPLY[@]}"' -- "$cur"))
@@ -339,7 +339,7 @@ _cvs()
 
             if [[ $cur != -* ]]; then
                 # starts with same algorithm as checkout
-                ! "$has_cvsroot" && cvsroot=${CVSROOT-}
+                [[ ! $has_cvsroot ]] && cvsroot=${CVSROOT-}
                 local prefix=${cur%/*}
                 if [[ -r ${cvsroot}/${prefix} ]]; then
                     _cvs_modules
diff --git a/completions/dmypy b/completions/dmypy
index cd6a62adf41..af9288b2f30 100644
--- a/completions/dmypy
+++ b/completions/dmypy
@@ -15,11 +15,11 @@ _comp_cmd_dmypy()
             ;;
     esac
 
-    local cmd has_cmd=false i
+    local cmd has_cmd="" i
     for ((i = 1; i < cword; i++)); do
         if [[ ${words[i]} != -* && ${words[i - 1]} != --status-file ]]; then
             cmd=${words[i]}
-            has_cmd=true
+            has_cmd=set
             break
         fi
     done
@@ -36,7 +36,7 @@ _comp_cmd_dmypy()
         return
     fi
 
-    if ! "$has_cmd"; then
+    if [[ ! $has_cmd ]]; then
         local cmds=$("$1" --help 2>&1 |
             command sed -ne '/positional arguments/{p;n;p;q;}' |
             command sed -ne 's/{\(.*\)}/\1/p')
diff --git a/completions/export b/completions/export
index 28ad8b84a5c..bc9907a707d 100644
--- a/completions/export
+++ b/completions/export
@@ -5,7 +5,7 @@ _comp_cmd_export()
     local cur prev words cword comp_args
     _comp_initialize -n := -- "$@" || return
 
-    local i action=variable remove=false
+    local i action=variable remove=""
     for ((i = 1; i < cword; i++)); do
         case ${words[i]} in
             -p)
@@ -15,7 +15,7 @@ _comp_cmd_export()
                 action=function
                 ;;&
             -*n*)
-                remove=true
+                remove=set
                 ;;
             -*)
                 continue
@@ -52,7 +52,7 @@ _comp_cmd_export()
                 return
             fi
             local suffix=""
-            if ! $remove && [[ $action != function ]]; then
+            if [[ ! $remove && $action != function ]]; then
                 suffix="="
                 compopt -o nospace
             fi
diff --git a/completions/find b/completions/find
index 646eefb1d5b..f229b04e0e8 100644
--- a/completions/find
+++ b/completions/find
@@ -64,14 +64,14 @@ _comp_cmd_find()
             ;;
     esac
 
-    local i exprfound=false
+    local i exprfound=""
     # set exprfound to true if there is already an expression present
     for i in "${words[@]}"; do
-        [[ $i == [-\(\),\!]* ]] && exprfound=true && break
+        [[ $i == [-\(\),\!]* ]] && exprfound=set && break
     done
 
     # handle case where first parameter is not a dash option
-    if ! $exprfound && [[ $cur != [-\(\),\!]* ]]; then
+    if [[ ! $exprfound && $cur != [-\(\),\!]* ]]; then
         _filedir -d
         return
     fi
diff --git a/completions/fio b/completions/fio
index b2a56d79814..14a0d71e4ba 100644
--- a/completions/fio
+++ b/completions/fio
@@ -115,17 +115,17 @@ _comp_cmd_fio()
                     # For example, for --kb_base=:
                     #        valid values: 1024       [...]
                     #                    : 1000       [...]
-                    local line="" in_values=false
+                    local line="" in_values=""
                     ret=()
                     for line in "${cmdhelp[@]}"; do
-                        if $in_values; then
+                        if [[ $in_values ]]; then
                             if [[ $line =~ ^[[:space:]]*:[[:space:]]*([^[:space:]]+) ]]; then
                                 ret+=("${BASH_REMATCH[1]}")
                             else
                                 break
                             fi
                         elif [[ $line =~ ^[[:space:]]*valid\ values:[[:space:]]*([^[:space:]]+) ]]; then
-                            in_values=true
+                            in_values=set
                             ret+=("${BASH_REMATCH[1]}")
                         fi
                     done
diff --git a/completions/getent b/completions/getent
index 102398b1444..7749b0da966 100644
--- a/completions/getent
+++ b/completions/getent
@@ -6,7 +6,7 @@ _comp_cmd_getent()
     _comp_initialize -s -- "$@" || return
 
     local noargopts='!(-*|*[s]*)'
-    local i db has_db=false
+    local i db has_db=""
     for ((i = 1; i < cword; i++)); do
         # shellcheck disable=SC2254
         case ${words[i]} in
@@ -21,7 +21,7 @@ _comp_cmd_getent()
             *)
                 # First non-option value is the db
                 db=${words[i]}
-                has_db=true
+                has_db=set
                 break
                 ;;
         esac
@@ -69,7 +69,7 @@ _comp_cmd_getent()
     if [[ $cur == -* ]]; then
         COMPREPLY=($(compgen -W '$(_parse_help "$1")' -- "$cur"))
         [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
-    elif ! "$has_db"; then
+    elif [[ ! $has_db ]]; then
         COMPREPLY=($(compgen -W 'passwd group hosts services protocols
             networks ahosts ahostsv4 ahostsv6 aliases ethers netgroup rpc
             shadow gshadow' -- "$cur"))
diff --git a/completions/ip b/completions/ip
index 4d0379f62f8..96ef3899131 100644
--- a/completions/ip
+++ b/completions/ip
@@ -43,16 +43,16 @@ _ip()
             ;;
     esac
 
-    local subcword cmd="" has_cmd=false subcmd=""
+    local subcword cmd="" has_cmd="" subcmd=""
     for ((subcword = 1; subcword < ${#words[@]} - 1; subcword++)); do
         [[ ${words[subcword]} == -b?(atch) ]] && return
-        "$has_cmd" && subcmd=${words[subcword]} && break
+        [[ $has_cmd ]] && subcmd=${words[subcword]} && break
         [[ ${words[subcword]} != -* &&
             ${words[subcword - 1]} != -@(f?(amily)|rc?(vbuf)) ]] &&
-            cmd=${words[subcword]} has_cmd=true
+            cmd=${words[subcword]} has_cmd=set
     done
 
-    if ! "$has_cmd"; then
+    if [[ ! $has_cmd ]]; then
         case $cur in
             -*)
                 local force=""
diff --git a/completions/ipmitool b/completions/ipmitool
index 4f8c4c66728..b0962f2d211 100644
--- a/completions/ipmitool
+++ b/completions/ipmitool
@@ -67,15 +67,15 @@ _ipmitool()
     local cmds=(raw i2c spd lan chassis power event mc sdr sensor fru gendev
         sel pef sol tsol isol user channel session sunoem kontronoem picmg fwum
         firewall shell exec set hpm ekanalyzer)
-    local i c cmd="" has_cmd=false subcmd
+    local i c cmd="" has_cmd="" subcmd
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
-        "$has_cmd" && subcmd=${words[i]} && break
+        [[ $has_cmd ]] && subcmd=${words[i]} && break
         for c in "${cmds[@]}"; do
-            [[ ${words[i]} == "$c" ]] && cmd=$c has_cmd=true && break
+            [[ ${words[i]} == "$c" ]] && cmd=$c has_cmd=set && break
         done
     done
 
-    if ! "$has_cmd"; then
+    if [[ ! $has_cmd ]]; then
         COMPREPLY=($(compgen -W '"${cmds[@]}"' -- "$cur"))
         return
     fi
diff --git a/completions/jarsigner b/completions/jarsigner
index bef320703fe..2c06920dd5c 100644
--- a/completions/jarsigner
+++ b/completions/jarsigner
@@ -31,16 +31,16 @@ _jarsigner()
     esac
 
     # Check if a jar was already given.
-    local i jar=false
+    local i jar=""
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         if [[ ${words[i]} == *.@(jar|apk) &&
             ${words[i - 1]} != -signedjar ]]; then
-            jar=true
+            jar=set
             break
         fi
     done
 
-    if ! $jar; then
+    if [[ ! $jar ]]; then
         if [[ $cur == -* ]]; then
             # Documented as "should not be used": -internalsf, -sectionsonly
             COMPREPLY=($(compgen -W '-keystore -storepass -storetype
diff --git a/completions/koji b/completions/koji
index db8d1d7d12c..7033b819b98 100644
--- a/completions/koji
+++ b/completions/koji
@@ -37,11 +37,11 @@ _koji()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local commandix command="" has_command=false
+    local commandix command="" has_command=""
     for ((commandix = 1; commandix < cword; commandix++)); do
         if [[ ${words[commandix]} != -* ]]; then
             command=${words[commandix]}
-            has_command=true
+            has_command=set
             break
         fi
     done
@@ -108,7 +108,7 @@ _koji()
 
     $split && return
 
-    if "$has_command"; then
+    if [[ $has_command ]]; then
         if [[ $cur == -* ]]; then
             COMPREPLY=($(compgen -W \
                 '$(_parse_help "$1" "$command --help")' -- "$cur"))
@@ -238,7 +238,7 @@ _koji()
     if [[ $cur == -* ]]; then
         COMPREPLY=($(compgen -W '$(_parse_help "$1")' -- "$cur"))
         [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
-    elif ! "$has_command"; then
+    elif [[ ! $has_command ]]; then
         COMPREPLY=($(compgen -W '$("$1" --help-commands 2>/dev/null | \
             awk "/^(  +|\t)/ { print \$1 }")' -- "$cur"))
     fi
diff --git a/completions/lzip b/completions/lzip
index 3f33ae2fe63..09b62705762 100644
--- a/completions/lzip
+++ b/completions/lzip
@@ -5,7 +5,7 @@ _lzip()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local decompress=false
+    local decompress=""
 
     local noargopts='!(-*|*[bmsSBdno]*)'
     # shellcheck disable=SC2254
@@ -15,7 +15,7 @@ _lzip()
             return
             ;;
         --decompress | -${noargopts}d)
-            decompress=true
+            decompress=set
             ;;
         --threads | -${noargopts}n)
             COMPREPLY=($(compgen -W "{1..$(_ncpus)}" -- "$cur"))
@@ -35,7 +35,7 @@ _lzip()
         return
     fi
 
-    if $decompress; then
+    if [[ $decompress ]]; then
         _filedir lz
         return
     fi
diff --git a/completions/make b/completions/make
index a54e04685ad..aa87eeb0fdc 100644
--- a/completions/make
+++ b/completions/make
@@ -111,7 +111,7 @@ _comp_make__truncate_non_unique_paths()
         for target in "${COMPREPLY[@]}"; do
             local path=${target%/}
             while [[ ! ${paths[$path]+set} ]] &&
-                paths[$path]=1 &&
+                paths[$path]=set &&
                 [[ $path == "$prefix"*/* ]]; do
                 path=${path%/*}
                 nchild[$path]=$((${nchild[$path]-0} + 1))
diff --git a/completions/mcrypt b/completions/mcrypt
index 75a3e0c54b8..de990d4afe4 100644
--- a/completions/mcrypt
+++ b/completions/mcrypt
@@ -49,15 +49,15 @@ _mcrypt()
     elif [[ ${words[0]} == mdecrypt ]]; then
         _filedir nc
     else
-        local i decrypt=0
+        local i decrypt=""
         for ((i = 1; i < ${#words[@]} - 1; i++)); do
             if [[ ${words[i]} == -@(d|-decrypt) ]]; then
                 _filedir nc
-                decrypt=1
+                decrypt=set
                 break
             fi
         done
-        if ((decrypt == 0)); then
+        if [[ ! $decrypt ]]; then
             _filedir
         fi
     fi
diff --git a/completions/mr b/completions/mr
index 1f6fb09cb23..18a92d3d584 100644
--- a/completions/mr
+++ b/completions/mr
@@ -21,17 +21,17 @@ _mr()
 
     # Determine if user has entered an `mr` command. Used to block top-level
     # (option and command) completions.
-    local cmd has_cmd=false i
+    local cmd has_cmd="" i
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         if [[ $commands == *"${words[i]}"* ]]; then
             cmd="${words[i]}"
-            has_cmd=true
+            has_cmd=set
             break
         fi
     done
 
     # Complete options for specific commands.
-    if "$has_cmd"; then
+    if [[ $has_cmd ]]; then
         case $cmd in
             bootstrap)
                 _filedir
diff --git a/completions/mutt b/completions/mutt
index 70ac3983d94..cb7a7807592 100644
--- a/completions/mutt
+++ b/completions/mutt
@@ -64,8 +64,8 @@ _comp_cmd_mutt__get_conffiles()
 # @var[ref] visited    Dictionary of config files already visited
 _comp_cmd_mutt__get_conffiles__visit()
 {
-    [[ -f $1 && ${visited[$1]-} != yes ]] || return 0
-    visited[$1]=yes
+    [[ -f $1 && ${visited[$1]-} != set ]] || return 0
+    visited[$1]=set
     conffiles+=("$1")
 
     local -a newconffiles=($(command sed -n 's|^source[[:space:]]\{1,\}\([^[:space:]]\{1,\}\).*$|\1|p' "$1"))
diff --git a/completions/pack200 b/completions/pack200
index 18481596b99..66dc9d4e977 100644
--- a/completions/pack200
+++ b/completions/pack200
@@ -45,15 +45,15 @@ _pack200()
     $split && return
 
     # Check if a pack or a jar was already given.
-    local i pack=false jar=false
+    local i pack="" jar=""
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         case ${words[i]} in
-            *.pack | *.pack.gz) pack=true ;;
-            *.jar) jar=true ;;
+            *.pack | *.pack.gz) pack=set ;;
+            *.jar) jar=set ;;
         esac
     done
 
-    if ! $pack; then
+    if [[ ! $pack ]]; then
         if [[ $cur == -* ]]; then
             COMPREPLY=($(compgen -W '--no-gzip --gzip --strip-debug
                 --no-keep-file-order --segment-limit= --effort= --deflate-hint=
@@ -65,7 +65,7 @@ _pack200()
         else
             _filedir 'pack?(.gz)'
         fi
-    elif ! $jar; then
+    elif [[ ! $jar ]]; then
         _filedir jar
     fi
 } &&
diff --git a/completions/postcat b/completions/postcat
index 5d75dc31383..8d5e112e11f 100644
--- a/completions/postcat
+++ b/completions/postcat
@@ -17,11 +17,11 @@ _postcat()
         return
     fi
 
-    local idx qfile=0
+    local idx qfile=""
     for idx in "${words[@]}"; do
-        [[ $idx == -q ]] && qfile=1 && break
+        [[ $idx == -q ]] && qfile=set && break
     done
-    if ((qfile == 1)); then
+    if [[ $qfile ]]; then
         local len=${#cur} pval
         for pval in $(mailq 2>/dev/null |
             command sed -e '1d; $d; /^[^0-9A-Z]/d; /^$/d; s/[* !].*$//'); do
diff --git a/completions/pytest b/completions/pytest
index 02c121a48ed..3a1ecb87b3d 100644
--- a/completions/pytest
+++ b/completions/pytest
@@ -103,16 +103,16 @@ _pytest()
 
     if [[ $cur == *.py::*:* ]]; then
         local file=${cur/.py:*/.py}
-        local class=${cur#*.py::} in_class=false
+        local class=${cur#*.py::} in_class=""
         local line
         class=${class%%:*}
         while IFS= read -r line; do
             if [[ $line =~ ^class[[:space:]]+${class}[[:space:]:\(] ]]; then
-                in_class=true
+                in_class=set
             elif [[ $line =~ ^class[[:space:]] ]]; then
-                in_class=false
+                in_class=""
             fi
-            if $in_class && [[ $line =~ ^[[:space:]]+(async[[:space:]]+)?def[[:space:]]+(test_[A-Za-z0-9_]+) ]]; then
+            if [[ $in_class && $line =~ ^[[:space:]]+(async[[:space:]]+)?def[[:space:]]+(test_[A-Za-z0-9_]+) ]]; then
                 COMPREPLY+=(${BASH_REMATCH[2]})
             fi
         done 2>/dev/null <"$file"
diff --git a/completions/route b/completions/route
index 6a938bb877d..44ae4f334a8 100644
--- a/completions/route
+++ b/completions/route
@@ -16,11 +16,11 @@ _route()
     local opt found i
     for opt in add del -host -net netmask metric mss window irtt reject mod \
         dyn reinstate dev default gw; do
-        found=false
+        found=""
         for ((i = 1; i < ${#words[@]} - 1; i++)); do
-            [[ ${words[i]} == "$opt" ]] && found=true && break
+            [[ ${words[i]} == "$opt" ]] && found=set && break
         done
-        $found || COMPREPLY+=("$opt")
+        [[ $found ]] || COMPREPLY+=("$opt")
     done
 
     ((${#COMPREPLY[@]})) &&
diff --git a/completions/secret-tool b/completions/secret-tool
index 4617c336d4a..1be538cc339 100644
--- a/completions/secret-tool
+++ b/completions/secret-tool
@@ -8,14 +8,14 @@ _secret_tool()
     $split && return
 
     local -i i
-    local mode="" has_mode=false word
+    local mode="" has_mode="" word
     for i in ${!words[*]}; do
         if [[ $i -gt 0 && ${words[i]} != -* ]]; then
-            ((i != cword)) && mode=${words[i]} has_mode=true
+            ((i != cword)) && mode=${words[i]} has_mode=set
             break
         fi
     done
-    if ! "$has_mode"; then
+    if [[ ! $has_mode ]]; then
         local -a modes
         modes=($("$1" nonexistent-mode 2>&1 |
             while read -r first second third rest; do
diff --git a/completions/ssh b/completions/ssh
index 4c34a02d615..77f417b79eb 100644
--- a/completions/ssh
+++ b/completions/ssh
@@ -480,16 +480,16 @@ _comp_xfunc_ssh_scp_local_files()
 {
     local IFS=$'\n'
 
-    local dirsonly=false
+    local dirsonly=""
     if [[ ${1-} == -d ]]; then
-        dirsonly=true
+        dirsonly=set
         shift
     fi
 
     local files
     _comp_expand_glob files '"$cur"*'
     ((${#files[@]})) || return 0
-    if $dirsonly; then
+    if [[ $dirsonly ]]; then
         COMPREPLY+=($(command ls -aF1dL "${files[@]}" 2>/dev/null |
             command sed -e "s/$_comp_cmd_scp__path_esc/\\\\&/g" -e '/[^\/]$/d' \
                 -e "s/^/${1-}/"))
diff --git a/completions/strace b/completions/strace
index 349f2416290..1f43118c56b 100644
--- a/completions/strace
+++ b/completions/strace
@@ -40,7 +40,7 @@ _strace()
                             while read -r define syscall rest; do
                                 [[ $define == "#define" &&
                                     $syscall =~ ^__NR_(.+) ]] &&
-                                    syscalls[${BASH_REMATCH[1]}]=1
+                                    syscalls[${BASH_REMATCH[1]}]=set
                             done 2>/dev/null </usr/include/asm/unistd.h
                             if ((${#syscalls[@]} == 0)); then
                                 local unistd arch=$(command uname -m)
@@ -52,7 +52,7 @@ _strace()
                                 while read -r define syscall rest; do
                                     [[ $define == "#define" &&
                                         $syscall =~ ^__NR_(.+) ]] &&
-                                        syscalls[${BASH_REMATCH[1]}]=1
+                                        syscalls[${BASH_REMATCH[1]}]=set
                                 done 2>/dev/null <$unistd
                             fi
 
diff --git a/completions/svcadm b/completions/svcadm
index 115f90680d8..b29fdde13e7 100644
--- a/completions/svcadm
+++ b/completions/svcadm
@@ -29,7 +29,7 @@ _smf_complete_fmri()
     if [[ $cur == $prefix* ]]; then
         [[ $cur == "$prefix" ]] && cur+="/"
         pattern="$cur*"
-        exact_mode=1
+        exact_mode=set
     else
         pattern="$prefix*/$cur*"
     fi
diff --git a/completions/sysbench b/completions/sysbench
index 21c8a6c682c..afa6261864c 100644
--- a/completions/sysbench
+++ b/completions/sysbench
@@ -105,23 +105,23 @@ _sysbench()
     esac
 
     # find out which test we're running
-    local i test="" has_test=false
+    local i test="" has_test=""
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         # TODO --test= is deprecated, bare test name preferred
         if [[ ${words[i]} == --test* ]]; then
             test=${words[i]#*=}
-            has_test=true
+            has_test=set
             break
         fi
     done
 
     local opts=$(_parse_help "$1")
-    if "$has_test"; then
+    if [[ $has_test ]]; then
         local help=($(_parse_help "$1" "--test=$test help"))
         opts="${opts/--test=/} ${help[*]} prepare run cleanup help version"
     fi
 
-    if [[ $cur == -* ]] || ! "$has_test"; then
+    if [[ $cur == -* || ! $has_test ]]; then
         COMPREPLY=($(compgen -W "$opts" -- "$cur"))
         [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
     else
diff --git a/completions/tar b/completions/tar
index e9feebb1333..b826a36e1a7 100644
--- a/completions/tar
+++ b/completions/tar
@@ -171,16 +171,16 @@ __tar_parse_old_opt()
 
     # current word is the first word
     [[ $cword -eq 1 && $cur && ${cur:0:1} != '-' ]] &&
-        old_opt_progress=1
+        old_opt_progress=set
 
     # check that first argument does not begin with "-"
     first_word=${words[1]}
     [[ $first_word && ${first_word:0:1} != "-" ]] &&
-        old_opt_used=1
+        old_opt_used=set
 
     # parse the old option (if present) contents to allow later code expect
     # corresponding arguments
-    if ((old_opt_used == 1)); then
+    if [[ $old_opt_used ]]; then
         char=${first_word:0:1}
         while [[ $char ]]; do
             if __tar_is_argreq "$char"; then
@@ -195,13 +195,12 @@ __tar_parse_old_opt()
 # Make the analysis of whole command line.
 __tar_preparse_cmdline()
 {
-    local first_arg i modes="ctxurdA"
+    local first_arg=set i modes="ctxurdA"
 
     shift # progname
 
     __tar_parse_old_opt
 
-    first_arg=1
     for i in "$@"; do
         case "$i" in
             --delete | --test-label)
@@ -220,14 +219,14 @@ __tar_preparse_cmdline()
                 ;;
             *[$modes]*)
                 # Only the first arg may be "MODE" without leading dash
-                if ((first_arg == 1)); then
+                if [[ $first_arg ]]; then
                     tar_mode=${i//[^$modes]/}
                     tar_mode=${tar_mode:0:1}
                     tar_mode_arg=$i
                 fi
                 ;;
         esac
-        first_arg=0
+        first_arg=""
     done
 }
 
@@ -306,7 +305,7 @@ __tar_complete_mode()
 
     # The last short option requires argument, like '-cf<TAB>'.  Cut the
     # completion here to enforce argument processing.
-    if ((old_opt_progress == 0)) &&
+    if [[ ! $old_opt_progress ]] &&
         __tar_is_argreq "$(__tar_last_char "$cur")"; then
         COMPREPLY=("$cur") && return 0
     fi
@@ -383,7 +382,7 @@ __tar_adjust_PREV_from_old_option()
     # deal with old style arguments here
     # $ tar cfTC # expects this sequence of arguments:
     # $ tar cfTC ARCHIVE_FILE PATTERNS_FILE CHANGE_DIR
-    if ((old_opt_used == 1 && cword > 1 && cword < ${#old_opt_parsed[@]} + 2)); then
+    if [[ $old_opt_used ]] && ((cword > 1 && cword < ${#old_opt_parsed[@]} + 2)); then
         # make e.g. 'C' option from 'cffCT'
         prev="-${old_opt_parsed[cword - 2]}"
     fi
@@ -488,8 +487,8 @@ _gtar()
     local long_opts short_opts basic_tar="" \
         long_arg_none="" long_arg_opt="" long_arg_req="" \
         short_arg_none="" short_arg_opt="" short_arg_req="" \
-        tar_mode tar_mode_arg old_opt_progress=0 \
-        old_opt_used=0 old_opt_parsed=()
+        tar_mode tar_mode_arg old_opt_progress="" \
+        old_opt_used="" old_opt_parsed=()
 
     # Main mode, e.g. -x or -c (extract/creation)
     local tar_mode=none
@@ -675,11 +674,11 @@ __tar_posix_prev_handle()
 
 _posix_tar()
 {
-    local long_opts short_opts basic_tar="" \
+    local long_opts short_opts basic_tar=set \
         long_arg_none="" long_arg_opt long_arg_req="" \
         short_arg_none short_arg_opt short_arg_req \
-        tar_mode tar_mode_arg old_opt_progress=0 \
-        old_opt_used=1 old_opt_parsed=()
+        tar_mode tar_mode_arg old_opt_progress="" \
+        old_opt_used=set old_opt_parsed=()
 
     # Main mode, e.g. -x or -c (extract/creation)
     local tar_mode=none
@@ -691,7 +690,6 @@ _posix_tar()
 
     _comp_initialize -s -- "$@" || return
 
-    basic_tar=yes
     tar_mode=none
 
     # relatively compatible modes are {c,t,x}
diff --git a/completions/timeout b/completions/timeout
index 0929143b01d..98e51adb5c7 100644
--- a/completions/timeout
+++ b/completions/timeout
@@ -2,17 +2,17 @@
 
 _timeout()
 {
-    local cur prev words cword split comp_args i found=false
+    local cur prev words cword split comp_args i found=""
     _comp_initialize -s -- "$@" || return
 
     local noargopts='!(-*|*[ks]*)'
     for ((i = 1; i <= COMP_CWORD; i++)); do
         if [[ ${COMP_WORDS[i]} != -* && ${COMP_WORDS[i - 1]} != = ]]; then
-            if $found; then
+            if [[ $found ]]; then
                 _comp_command_offset $i
                 return
             fi
-            found=true
+            found=set
         fi
         # shellcheck disable=SC2254
         [[ ${COMP_WORDS[i]} == -@(-kill-after|-signal|${noargopts}[ks]) ]] && ((i++))
diff --git a/completions/unpack200 b/completions/unpack200
index 9ad1121ff15..b3d4708c01d 100644
--- a/completions/unpack200
+++ b/completions/unpack200
@@ -25,15 +25,15 @@ _unpack200()
     $split && return
 
     # Check if a pack or a jar was already given.
-    local word pack=false jar=false
+    local word pack="" jar=""
     for word in "${words[@]:1}"; do
         case $word in
-            *.pack | *.pack.gz) pack=true ;;
-            *.jar) jar=true ;;
+            *.pack | *.pack.gz) pack=set ;;
+            *.jar) jar=set ;;
         esac
     done
 
-    if ! $pack; then
+    if [[ ! $pack ]]; then
         if [[ $cur == -* ]]; then
             COMPREPLY=($(compgen -W '--deflate-hint= --remove-pack-file
                 --verbose --quiet --log-file= --help --version' -- "$cur"))
@@ -41,7 +41,7 @@ _unpack200()
         else
             _filedir 'pack?(.gz)'
         fi
-    elif ! $jar; then
+    elif [[ ! $jar ]]; then
         _filedir jar
     fi
 } &&
diff --git a/completions/upgradepkg b/completions/upgradepkg
index 9dc2b84f967..a2e7e61eaf6 100644
--- a/completions/upgradepkg
+++ b/completions/upgradepkg
@@ -17,7 +17,7 @@ _upgradepkg()
         local nofiles="" IFS=$'\n'
         compopt -o filenames
         COMPREPLY=($(compgen -P "$prev%" -f -X "!*.@(t[bgxl]z)" -- "$cur"))
-        [[ ${COMPREPLY-} ]] || nofiles=1
+        [[ ${COMPREPLY-} ]] || nofiles=set
         COMPREPLY+=($(compgen -P "$prev%" -S '/' -d -- "$cur"))
         [[ $nofiles ]] && compopt -o nospace
         return
diff --git a/completions/useradd b/completions/useradd
index fd91bb7c76c..d2ec6fdc6b3 100644
--- a/completions/useradd
+++ b/completions/useradd
@@ -8,13 +8,13 @@ _useradd()
     # TODO: if -o/--non-unique is given, could complete on existing uids
     #       with -u/--uid
 
-    local word chroot="" has_chroot=false
+    local word chroot="" has_chroot=""
     for word in "${words[@]}"; do
-        if "$has_chroot"; then
+        if [[ $has_chroot ]]; then
             chroot=$word
             break
         fi
-        [[ $word != -@(R|-root) ]] || has_chroot=true
+        [[ $word != -@(R|-root) ]] || has_chroot=set
     done
 
     local noargopts='!(-*|*[cefKpubdkRgGZs]*)'
diff --git a/completions/usermod b/completions/usermod
index adf8231e07d..8938e339ca2 100644
--- a/completions/usermod
+++ b/completions/usermod
@@ -8,13 +8,13 @@ _usermod()
     # TODO: if -o/--non-unique is given, could complete on existing uids
     #       with -u/--uid
 
-    local word chroot="" has_chroot=false
+    local word chroot="" has_chroot=""
     for word in "${words[@]}"; do
-        if "$has_chroot"; then
+        if [[ $has_chroot ]]; then
             chroot=$word
             break
         fi
-        [[ $word != -@(R|-root) ]] || has_chroot=true
+        [[ $word != -@(R|-root) ]] || has_chroot=set
     done
 
     local noargopts='!(-*|*[cdeflpugGRZs]*)'
diff --git a/completions/wodim b/completions/wodim
index 80187a13d3d..5741703747f 100644
--- a/completions/wodim
+++ b/completions/wodim
@@ -66,15 +66,15 @@ _cdrecord()
         -isosize -pad -nopad -shorttrack -noshorttrack -preemp -nopreemp
         -copy -nocopy -scms "isrc=" "index=" "padsize=" "pregap=" "tsize=")
     # look if previous was either a file or a track option
-    track_mode=0
+    track_mode=""
     if ((cword > 1)); then
         if [[ -f $prev ]]; then
-            track_mode=1
+            track_mode=set
         else
             local opt
             for opt in "${track_options[@]}"; do
                 if [[ $opt == "$prev" ]]; then
-                    track_mode=1
+                    track_mode=set
                     break
                 fi
             done
@@ -86,7 +86,7 @@ _cdrecord()
     # track options are always available
     COMPREPLY+=($(compgen -W '"${track_options[@]}"' -- "$cur"))
     # general options are no more available after file or track option
-    if ((track_mode == 0)); then
+    if [[ ! $track_mode ]]; then
         COMPREPLY+=($(compgen -W '"${generic_options[@]}"' -- "$cur"))
     fi
     [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
diff --git a/completions/wtf b/completions/wtf
index 1e3b844d18f..825e795a5f4 100644
--- a/completions/wtf
+++ b/completions/wtf
@@ -13,7 +13,7 @@ _wtf()
         return
     fi
 
-    local db="" has_db=false
+    local db="" has_db=""
 
     set -- "${words[@]}"
     while (($# > 0)); do
@@ -21,20 +21,20 @@ _wtf()
             shift
             if (($# > 0)); then
                 db=$1
-                has_db=true
+                has_db=set
             fi
             break
         fi
         shift
     done
 
-    if ! "$has_db"; then
+    if [[ ! $has_db ]]; then
         local f
         for f in "${ACRONYMDB-}" /usr/share/misc/acronyms \
             /usr/share/games/bsdgames/acronyms; do
-            [[ -f $f ]] && db="$f" has_db=true && break
+            [[ -f $f ]] && db="$f" has_db=set && break
         done
-        "$has_db" || return
+        [[ $has_db ]] || return
     fi
 
     COMPREPLY=($(compgen -W "$(cut -f 1 -s "$db"* 2>/dev/null) $addf" \
diff --git a/completions/xrandr b/completions/xrandr
index 6b1e6a84edc..b0a4b576f41 100644
--- a/completions/xrandr
+++ b/completions/xrandr
@@ -46,11 +46,11 @@ _xrandr()
     local cur prev words cword comp_args
     _comp_initialize -- "$@" || return
 
-    local i output has_output=false
+    local i output has_output=""
     for ((i = cword - 1; i > 0; i--)); do
         if [[ ${words[i]} == --output ]]; then
             output=${words[i + 1]}
-            has_output=true
+            has_output=set
             break
         fi
     done
@@ -67,14 +67,14 @@ _xrandr()
             return
             ;;
         --left-of | --right-of | --above | --below | --same-as)
-            if "$has_output"; then
+            if [[ $has_output ]]; then
                 local outputs=$(_comp_cmd_xrandr_outputs "$1")
                 COMPREPLY=($(compgen -W "$outputs" -- "$cur"))
             fi
             return
             ;;
         --mode)
-            if "$has_output"; then
+            if [[ $has_output ]]; then
                 local modes=$(_comp_cmd_xrandr_modes "$1" "$output")
                 COMPREPLY=($(compgen -W "$modes" -- "$cur"))
             fi
@@ -87,19 +87,19 @@ _xrandr()
             return
             ;;
         --reflect)
-            if "$has_output"; then
+            if [[ $has_output ]]; then
                 COMPREPLY=($(compgen -W 'normal x y xy' -- "$cur"))
             fi
             return
             ;;
         --rotate)
-            if "$has_output"; then
+            if [[ $has_output ]]; then
                 COMPREPLY=($(compgen -W 'normal inverted left right' -- "$cur"))
             fi
             return
             ;;
         --filter)
-            if "$has_output"; then
+            if [[ $has_output ]]; then
                 COMPREPLY=($(compgen -W 'bilinear nearest' -- "$cur"))
             fi
             return
@@ -171,7 +171,7 @@ _xrandr()
     fi
 
     local options
-    if "$has_output"; then
+    if [[ $has_output ]]; then
         options=$(
             _comp_cmd_xrandr_help "$1" |
                 command sed -e 's/ or /\n  /g' -e 's/<[^>]*>]//g' |