In /usr/bin/cdiff line 24:
        file=`echo "$1" | perl -pe 's|^file:/+|/|i'`
             ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
        file=$(echo "$1" | perl -pe 's|^file:/+|/|i')


In /usr/bin/cdiff line 30:
        case `echo "$file" | perl -ne 'print lc $_'` in
             ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
        case $(echo "$file" | perl -ne 'print lc $_') in

For more information:
  https://www.shellcheck.net/wiki/SC2006 -- Use $(...) notation instead of le...