In /usr/bin/xmlto line 20:
FIND=find      # This must be GNU find (need -maxdepth)
^--^ SC2209: Use var=$(command) to assign output (or quote to assign string).


In /usr/bin/xmlto line 21:
MKTEMP=mktemp # See http://www.mktemp.org if missing on your system
^----^ SC2034: MKTEMP appears unused. Verify use (or export if used externally).


In /usr/bin/xmlto line 24:
TAIL=/usr/bin/tail     # a tail that supports -n (posix)
^--^ SC2034: TAIL appears unused. Verify use (or export if used externally).


In /usr/bin/xmlto line 26:
SED=/bin/sed       # GNU sed, for modification of patterns
^-^ SC2034: SED appears unused. Verify use (or export if used externally).


In /usr/bin/xmlto line 82:
  [ "$1" = "-d" ] && { dirflag="-d"; shift; }
                       ^-----^ SC2034: dirflag appears unused. Verify use (or export if used externally).


In /usr/bin/xmlto line 85:
  if eval $2='$(${MKTEMP} $dirflag "${TMPDIR:-/tmp}/${prefix}.XXXXXX")'
          ^-- SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
  if eval "$2"='$(${MKTEMP} $dirflag "${TMPDIR:-/tmp}/${prefix}.XXXXXX")'


In /usr/bin/xmlto line 102:
  for asearchpath in "$1"; do
                     ^--^ SC2066: Since you double quoted this, it will not word split, and the loop will only run once.


In /usr/bin/xmlto line 120:
: ${FORMAT_DIR=${prefix}/share/xmlto/format}
  ^-- SC2223: This default assignment may cause DoS due to globbing. Quote it.


In /usr/bin/xmlto line 123:
: ${SOURCE_FORMAT=docbook}
  ^----------------------^ SC2223: This default assignment may cause DoS due to globbing. Quote it.


In /usr/bin/xmlto line 150:
  papername=`"$PAPERCONF_PATH" -n`
            ^--------------------^ SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
  papername=$("$PAPERCONF_PATH" -n)


In /usr/bin/xmlto line 151:
  paperheight=`"$PAPERCONF_PATH" -mh | sed 's/ //g'`
              ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
  paperheight=$("$PAPERCONF_PATH" -mh | sed 's/ //g')


In /usr/bin/xmlto line 152:
  paperwidth=`"$PAPERCONF_PATH" -mw | sed 's/ //g'`
             ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
  paperwidth=$("$PAPERCONF_PATH" -mw | sed 's/ //g')


In /usr/bin/xmlto line 154:
  if [ -n "$paperheight" -a -n "$paperwidth" ]
                         ^-- SC2166: Prefer [ p ] && [ q ] as [ p -a q ] is not well defined.


In /usr/bin/xmlto line 157:
    cat << EOF > "$papersizemod"
                  ^-----------^ SC2154: papersizemod is referenced but not assigned.


In /usr/bin/xmlto line 210:
      cat << EOF > "$encodingmod"
                    ^----------^ SC2154: encodingmod is referenced but not assigned.


In /usr/bin/xmlto line 261:
  if [ x`$FOP_PATH -v 2>/dev/null | $GREP 0_[12]` = x ]; then
        ^-- SC2046: Quote this to prevent word splitting.
        ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
  if [ x$($FOP_PATH -v 2>/dev/null | $GREP 0_[12]) = x ]; then


In /usr/bin/xmlto line 287:
[ $? != 0 ] && { usage; exit 1; }
  ^-- SC2181: Check exit code directly with e.g. 'if mycmd;', not indirectly with $?.


In /usr/bin/xmlto line 302:
	    cat /dev/stdin > ${TMP_STYLESHEET}
                             ^---------------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
	    cat /dev/stdin > "${TMP_STYLESHEET}"


In /usr/bin/xmlto line 340:
	VERBOSE=$((${VERBOSE}+1))
                   ^--------^ SC2004: $/${} is unnecessary on arithmetic variables.


In /usr/bin/xmlto line 425:
if [ -z "$DEST_FORMAT" -o -z "$INPUT_FILE" ]
                       ^-- SC2166: Prefer [ p ] || [ q ] as [ p -o q ] is not well defined.


In /usr/bin/xmlto line 453:
case $(echo $rootel) in
     ^-------------^ SC2116: Useless echo? Instead of 'cmd $(echo foo)', just use 'cmd foo'.
            ^-----^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
case $(echo "$rootel") in


In /usr/bin/xmlto line 503:
if [ -n "$XSL_MODS" -a -n "$STYLESHEET" ]
                    ^-- SC2166: Prefer [ p ] && [ q ] as [ p -a q ] is not well defined.


In /usr/bin/xmlto line 529:
cd "$XSLT_PROCESSED_DIR"
^----------------------^ SC2164: Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

Did you mean: 
cd "$XSLT_PROCESSED_DIR" || exit


In /usr/bin/xmlto line 556:
      exit $(($xmllint_status + 10))
              ^-------------^ SC2004: $/${} is unnecessary on arithmetic variables.


In /usr/bin/xmlto line 585:
    printf >&2 "${XSLTPROC_PATH} ${XSLTOPTS} ${SEARCHPATH_FORMATTED} \\\\\n -o \"${PROF_PROCESSED}\" \\\\\n \"${PROFILE_STYLESHEET}\" \"${INPUT_FILE}\"\n"
               ^-- SC2059: Don't use variables in the printf format string. Use printf '..%s..' "$foo".


In /usr/bin/xmlto line 611:
   printf >&2 "${XSLTPROC_PATH} ${XSLTOPTS} ${SEARCHPATH_FORMATTED} \\\\\n -o \"${XSLT_PROCESSED}\" \\\\\n \"${STYLESHEET}\" \\\\\n \"${PROF_PROCESSED}\"\n"
              ^-- SC2059: Don't use variables in the printf format string. Use printf '..%s..' "$foo".


In /usr/bin/xmlto line 626:
	printf >&2 "${XSLTPROC_PATH} ${XSLTOPTS} ${SEARCHPATH_FORMATTED}\\\\\n -o \"${XSLT_PROCESSED}\" \\\\\n \"${STYLESHEET}\" \\\\\n \"${PROF_PROCESSED}\"\n"
                   ^-- SC2059: Don't use variables in the printf format string. Use printf '..%s..' "$foo".


In /usr/bin/xmlto line 628:
    eval "\"${XSLTPROC_PATH}\"" ${XSLTOPTS} ${SEARCHPATH_FORMATTED} -o "\"${XSLT_PROCESSED}\"" "\"${STYLESHEET}\"" "\"${PROF_PROCESSED}\""
                                ^---------^ SC2086: Double quote to prevent globbing and word splitting.
                                            ^---------------------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
    eval "\"${XSLTPROC_PATH}\"" "${XSLTOPTS}" "${SEARCHPATH_FORMATTED}" -o "\"${XSLT_PROCESSED}\"" "\"${STYLESHEET}\"" "\"${PROF_PROCESSED}\""

For more information:
  https://www.shellcheck.net/wiki/SC2066 -- Since you double quoted this, it ...
  https://www.shellcheck.net/wiki/SC2034 -- MKTEMP appears unused. Verify use...
  https://www.shellcheck.net/wiki/SC2046 -- Quote this to prevent word splitt...