In /usr/bin/update-nfonts line 6:
if [ "`id`" != "`id root`" ]; then
      ^--^ SC2006: Use $(...) notation instead of legacy backticked `...`.
                ^-------^ SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
if [ "$(id)" != "$(id root)" ]; then


In /usr/bin/update-nfonts line 8:
    output=`echo ~/GNUstep/Library/Fonts/`
           ^-----------------------------^ SC2006: Use $(...) notation instead of legacy backticked `...`.
           ^-----------------------------^ SC2116: Useless echo? Instead of 'cmd $(echo foo)', just use 'cmd foo'.

Did you mean: 
    output=$(echo ~/GNUstep/Library/Fonts/)


In /usr/bin/update-nfonts line 12:
    cd $output
    ^--------^ SC2164: Use 'cd ... || exit' or 'cd ... || return' in case cd fails.
       ^-----^ SC2086: Double quote to prevent globbing and word splitting.

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


In /usr/bin/update-nfonts line 13:
    find $input -name "*.${z}" -type f -print | while read a; do
                                                      ^--^ SC2162: read without -r will mangle backslashes.


In /usr/bin/update-nfonts line 14:
	if test -f $a; then
                   ^-- SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
	if test -f "$a"; then


In /usr/bin/update-nfonts line 15:
	    bna=`basename "$a"`
                ^-------------^ SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
	    bna=$(basename "$a")


In /usr/bin/update-nfonts line 30:
	    mknfonts $b 2>/dev/null
                     ^-- SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
	    mknfonts "$b" 2>/dev/null


In /usr/bin/update-nfonts line 36:
    mknfonts $b 2>/dev/null
             ^-- SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
    mknfonts "$b" 2>/dev/null


In /usr/bin/update-nfonts line 52:
cd $output
^--------^ SC2164: Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

Did you mean: 
cd $output || exit


In /usr/bin/update-nfonts line 53:
find $input -name "$mask" -type f -print |while read a; do
                                                ^--^ SC2162: read without -r will mangle backslashes.


In /usr/bin/update-nfonts line 54:
    ln -s "$a" "`basename "$a"`" 2>/dev/null
                ^-------------^ SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
    ln -s "$a" "$(basename "$a")" 2>/dev/null

For more information:
  https://www.shellcheck.net/wiki/SC2164 -- Use 'cd ... || exit' or 'cd ... |...
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...
  https://www.shellcheck.net/wiki/SC2162 -- read without -r will mangle backs...