shellcheck errors and warnings

[debalance]

Great little tool, but could you make it shellcheck-clean?

$ shellcheck btrfs-sync

In btrfs-sync line 80:
[[ $? -ne 0 ]] && { echo "error parsing arguments"; exit 1; }
   ^-- SC2181 (style): Check exit code directly with e.g. 'if ! mycmd;', not indirectly with $?.


In btrfs-sync line 98:
DST="${@: -1}"
    ^--------^ SC2124 (warning): Assigning an array to a string! Assign as array, or use * instead of @ to concatenate.


In btrfs-sync line 101:
[[ "$SRC" =~ : ]] && {
    ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 102:
  NET_SRC="$( sed 's|:.*||' <<<"$SRC" )"
              ^---------------------^ SC2001 (style): See if you can use ${variable//search/replace} instead.
                                ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 103:
  SRC="$( sed 's|.*:||' <<<"$SRC" )"
  ^-^ SC2178 (warning): Variable was used as an array but is now assigned a string.
          ^---------------------^ SC2001 (style): See if you can use ${variable//search/replace} instead.
                            ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 107:
[[ "$SSH_SRC" != "" ]] && SRC_CMD=( ${SSH_SRC[@]} ) || SRC_CMD=( eval )
    ^------^ SC2128 (warning): Expanding an array without an index only gives the first element.
                                    ^-----------^ SC2206 (warning): Quote to prevent word splitting/globbing, or split robustly with mapfile or read -a.


In btrfs-sync line 108:
${SRC_CMD[@]} test -x "$SRC" &>/dev/null || {
^-----------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.
                       ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 109:
  [[ "$SSH_SRC" != "" ]] && echo "SSH access error to $NET_SRC. Do you have passwordless login setup, and adequate permissions for $SRC?"
      ^------^ SC2128 (warning): Expanding an array without an index only gives the first element.
                                                                                                                                   ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 110:
  [[ "$SSH_SRC" == "" ]] && echo "Access error. Do you have adequate permissions for $SRC?"
      ^------^ SC2128 (warning): Expanding an array without an index only gives the first element.
                                                                                     ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 116:
  NET="$( sed 's|:.*||' <<<"$DST" )"
          ^---------------------^ SC2001 (style): See if you can use ${variable//search/replace} instead.


In btrfs-sync line 117:
  DST="$( sed 's|.*:||' <<<"$DST" )"
          ^---------------------^ SC2001 (style): See if you can use ${variable//search/replace} instead.


In btrfs-sync line 120:
[[ "$SSH" != "" ]] && DST_CMD=( ${SSH[@]} ) || DST_CMD=( eval )
    ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.
                                ^-------^ SC2206 (warning): Quote to prevent word splitting/globbing, or split robustly with mapfile or read -a.


In btrfs-sync line 121:
${DST_CMD[@]} test -x "$DST" &>/dev/null || {
^-----------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.


In btrfs-sync line 122:
  [[ "$SSH" != "" ]] && echo "SSH access error to $NET. Do you have passwordless login setup, and adequate permissions for $DST?"
      ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 123:
  [[ "$SSH" == "" ]] && echo "Access error. Do you have adequate permissions for $DST?"
      ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 135:
${DST_CMD[@]} "pgrep -f btrfs\ receive &>/dev/null" && { echo "btrfs-sync already running at destination"; exit 1; }
^-----------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.


In btrfs-sync line 139:
while read entry; do SRCS+=( "$entry" ); done < <(
      ^--^ SC2162 (info): read without -r will mangle backslashes.


In btrfs-sync line 141:
    for s in "${SRC[@]}"; do
              ^-------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.
              ^-------^ SC2145 (error): Argument mixes string and array. Use * or separate argument.
              ^-------^ SC2027 (warning): The surrounding quotes actually unquote this. Remove or escape them.


In btrfs-sync line 157:
    "${SRC_CMD[@]}" type pbzip2 &>/dev/null && \
                                            ^-- SC2015 (info): Note that A && B || C is not if-then-else. C may run when A is true.


In btrfs-sync line 160:
      ZIP=xz PIZ=unxz
             ^-^ SC2178 (warning): Variable was used as an array but is now assigned a string.


In btrfs-sync line 178:
  while read entry; do
        ^--^ SC2162 (info): read without -r will mangle backslashes.


In btrfs-sync line 179:
    DST_UUIDS+=( "$( sed 's=|.*==' <<<"$entry" )" )
                     ^-----------------------^ SC2001 (style): See if you can use ${variable//search/replace} instead.


In btrfs-sync line 180:
    DSTS+=(      "$( sed 's=.*|==' <<<"$entry" )" )
                     ^-----------------------^ SC2001 (style): See if you can use ${variable//search/replace} instead.


In btrfs-sync line 193:
  local SRC="$1"
        ^-^ SC2178 (warning): Variable was used as an array but is now assigned a string.


In btrfs-sync line 200:
    local LIST="$( "${SRC_CMD[@]}" sudo btrfs subvolume list -su "$SRC" )"
          ^--^ SC2155 (warning): Declare and assign separately to avoid masking return values.
                                                                  ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 204:
        local PATH_=$( awk "{ if ( \$14 == \"$id\" ) print \$16       }" <<<"$LIST" )
              ^---^ SC2155 (warning): Declare and assign separately to avoid masking return values.


In btrfs-sync line 205:
        local DATE=$(  awk "{ if ( \$14 == \"$id\" ) print \$11, \$12 }" <<<"$LIST" )
              ^--^ SC2155 (warning): Declare and assign separately to avoid masking return values.


In btrfs-sync line 210:
            local PATHS=( $( "${SRC_CMD[@]}" sudo btrfs su list -u "$SRC" | awk '{ print $11 }' ) )
                          ^-- SC2207 (warning): Prefer mapfile or read -a to split command output (or quote to avoid splitting).
                                                                    ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 212:
              SHOWP="$( "${SRC_CMD[@]}" sudo btrfs su sh "$( dirname "$SRC" )/$( basename "$p" )" 2>/dev/null )"
              ^---^ SC2178 (warning): Variable was used as an array but is now assigned a string.
                                                                      ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 213:
              RXIDP="$( grep 'Received UUID' <<<"$SHOWP" | awk '{ print $3     }' )"
              ^---^ SC2178 (warning): Variable was used as an array but is now assigned a string.
                                                 ^----^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 214:
              DATEP="$( grep 'Creation time' <<<"$SHOWP" | awk '{ print $3, $4 }' )"
              ^---^ SC2178 (warning): Variable was used as an array but is now assigned a string.
                                                 ^----^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 215:
              [[ "$RXIDP" == "" ]] && continue
                  ^----^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 216:
              PATH_RXID["$RXIDP"]="$p"
                         ^----^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 217:
              DATE_RXID["$RXIDP"]="$DATEP"
                         ^----^ SC2128 (warning): Expanding an array without an index only gives the first element.
                                   ^----^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 225:
        [[ "$PATH_" == "" ]] || [[ "$PATH_" == "$( basename "$SRC" )" ]] && continue
                                                             ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 227:
        local SECS=$( date -d "$DATE" +"%s" )
              ^--^ SC2155 (warning): Declare and assign separately to avoid masking return values.


In btrfs-sync line 235:
  local SHOW="$( "${SRC_CMD[@]}" sudo btrfs subvolume show "$SRC" )"
        ^--^ SC2155 (warning): Declare and assign separately to avoid masking return values.
                                                            ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 237:
  local SRC_UUID="$( grep 'UUID:' <<<"$SHOW" | head -1 | awk '{ print $2 }' )"
        ^------^ SC2155 (warning): Declare and assign separately to avoid masking return values.


In btrfs-sync line 240:
  local SRC_RXID="$( grep 'Received UUID' <<<"$SHOW"   | awk '{ print $3 }' )"
        ^------^ SC2155 (warning): Declare and assign separately to avoid masking return values.


In btrfs-sync line 249:
  local SRC="$1"
        ^-^ SC2178 (warning): Variable was used as an array but is now assigned a string.


In btrfs-sync line 250:
  "${SRC_CMD[@]}" test -d "$SRC" || return
                           ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 252:
  exists_at_dst "$SRC" && { echov "* Skip existing '$SRC'"; return 0; }
                 ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.
                                                    ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 254:
  choose_seed "$SRC"  # sets SEED
               ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 258:
    local SEED_PATH="$( dirname "$SRC" )/$( basename $SEED )"
          ^-------^ SC2155 (warning): Declare and assign separately to avoid masking return values.
                                 ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.
                                                     ^---^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 
    local SEED_PATH="$( dirname "$SRC" )/$( basename "$SEED" )"


In btrfs-sync line 266:
  [[ "$SEED_ARG" != "" ]] && echov -n " using seed '$SEED'"
      ^-------^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 270:
  sudo btrfs send -q ${SEED_ARG[@]} "$SRC" \
                     ^------------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.
                                     ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 273:
    | "${DST_CMD[@]}" "${PIZ[@]} | sudo btrfs receive \"$DST\" 2>&1 |(grep -v -e'^At subvol ' -e'^At snapshot '||true)" \
                       ^-------^ SC2145 (error): Argument mixes string and array. Use * or separate argument.


In btrfs-sync line 275:
      "${DST_CMD[@]}" sudo btrfs subvolume delete "$DST"/"$( basename "$SRC" )" 2>/dev/null
                                                                       ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 280:
  DSTS+=("$DST/$( basename "$SRC" )")
                            ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 282:
  SEED_NEXT="$SRC"
             ^--^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 309:
  ${DST_CMD[@]} sudo btrfs subvolume delete "${PRUNE_LIST[@]}" $SILENT
  ^-----------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.
                                                               ^-----^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 
  ${DST_CMD[@]} sudo btrfs subvolume delete "${PRUNE_LIST[@]}" "$SILENT"


In btrfs-sync line 316:
      [[ "$( basename $src )" == "$( basename $dst )" ]] && { FOUND=1; break; }
                      ^--^ SC2086 (info): Double quote to prevent globbing and word splitting.
                                              ^--^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 
      [[ "$( basename "$src" )" == "$( basename "$dst" )" ]] && { FOUND=1; break; }


In btrfs-sync line 320:
[[ "$DEL_LIST" != "" ]] && \
    ^-------^ SC2128 (warning): Expanding an array without an index only gives the first element.


In btrfs-sync line 322:
  ${DST_CMD[@]} sudo btrfs subvolume delete "${DEL_LIST[@]}" $SILENT
  ^-----------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.
                                                             ^-----^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 
  ${DST_CMD[@]} sudo btrfs subvolume delete "${DEL_LIST[@]}" "$SILENT"

For more information:
  https://www.shellcheck.net/wiki/SC2068 -- Double quote array expansions to ...
  https://www.shellcheck.net/wiki/SC2145 -- Argument mixes string and array. ...
  https://www.shellcheck.net/wiki/SC2027 -- The surrounding quotes actually u...