In /usr/bin/geos-config line 3:
exec_prefix=${prefix}
^---------^ SC2034: exec_prefix appears unused. Verify use (or export if used externally).


In /usr/bin/geos-config line 4:
libdir=${prefix}/lib/x86_64-linux-gnu
^----^ SC2034: libdir appears unused. Verify use (or export if used externally).


In /usr/bin/geos-config line 23:
    exit $1
         ^-- SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
    exit "$1"


In /usr/bin/geos-config line 30:
    -*=*) optarg=`echo "$1" | sed 's/[-_a-zA-Z0-9]*=//'` ;;
                 ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean: 
    -*=*) optarg=$(echo "$1" | sed 's/[-_a-zA-Z0-9]*=//') ;;


In /usr/bin/geos-config line 31:
    *) optarg= ;;
       ^----^ SC2034: optarg appears unused. Verify use (or export if used externally).

For more information:
  https://www.shellcheck.net/wiki/SC2034 -- exec_prefix appears unused. Verif...
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...
  https://www.shellcheck.net/wiki/SC2006 -- Use $(...) notation instead of le...