In /usr/bin/anytopnm line 28:
fileextension=`echo "$1" | awk '{gsub(" ","");gsub(".*\\\\.",".");print}'`
              ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
fileextension=$(echo "$1" | awk '{gsub(" ","");gsub(".*\\\\.",".");print}')


In /usr/bin/anytopnm line 33:
if [ $# -eq 0 -o "$1" = "-" ] ; then
              ^-- SC2166: Prefer [ p ] || [ q ] as [ p -o q ] is not well defined.


In /usr/bin/anytopnm line 60:
filetype=`file "$file" | cut -d: -f2-`
         ^---------------------------^ SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
filetype=$(file "$file" | cut -d: -f2-)


In /usr/bin/anytopnm line 70:
    (echo begin 600 $newfile; sed 1d < "$file") | uudecode # #204890
                    ^------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
    (echo begin 600 "$newfile"; sed 1d < "$file") | uudecode # #204890


In /usr/bin/anytopnm line 187:
        *.fs | *.fs.* | *.face | *.face.* )
                        ^----^ SC2221: This pattern always overrides a later one on line 232.
                                 ^------^ SC2221: This pattern always overrides a later one on line 232.


In /usr/bin/anytopnm line 232:
        *.ybm | *.ybm.* | *.face | *.face.* )
                          ^----^ SC2222: This pattern never matches because of a previous pattern on line 187.
                                   ^------^ SC2222: This pattern never matches because of a previous pattern on line 187.

For more information:
  https://www.shellcheck.net/wiki/SC2166 -- Prefer [ p ] || [ q ] as [ p -o q...
  https://www.shellcheck.net/wiki/SC2221 -- This pattern always overrides a l...
  https://www.shellcheck.net/wiki/SC2222 -- This pattern never matches becaus...