bash unary operator expected, can't see anything wrong with if statement

Question

I've got some bash code and it doesn't seem to work, and I can't figure out why. There is something wrong with an if statement, but I can't make sense of it.

function param_err_non {
        echo "error: parameter missing"
        return 1
}

function param_err_many {
        echo "error: too many parameters"
        return 1
}

function param_err_invl {
        echo "error: invalid parameter"
        return 1
}

dbcmd=""
dbusr=""
dbste="" #this isn't so obvious, it's the site name
dbkey=""
dbval=""
nopar=0

if [ "$1" = "" ]; then param_err_non; fi

case "$1" in
        get)
                dbcmd=$1
                ;;                                                                                      
        put)                                                                                            
                dbcmd=$1                                                                                
                ;;                                                                                      
        del)                                                                                            
                dbcmd=$1                                                                                
                ;;                                                                                      
        new)                                                                                            
                dbcmd=$1                                                                                
                ;;                                                                                      
        list)                                                                                           
                dbcmd=$1                                                                                
                nopar=1                                                                                 
                ;;
        *)
                param_err_invl
esac

echo "running command $dbcmd"

if [ "$dbcmd" = "" ]; then param_err_non; fi

if [ "$2" = "" ]; then param_err_non; else dbusr=$2; fi

if [ $nopar -eq 0 ]; then
        if [ "$3" = "" ]; then param_err_non; else dbste=$3; fi
fi

counter=
for param in "$@"
do

        let counter=counter+1

        if [ "$dbcmd" = "del" ]; then
                echo "entering delete param check $counter"
                if [ "$3" = "" ]; then deleteall=1; else
                         if [ $counter -eq 4 ]; then param_err_many; fi
                fi
        fi

        if [ "$dbcmd" = "get" ]; then
                if [ $counter -eq 4 ]; then dbkey="$4"; fi
                if [ $counter -ge 5 ]; then param_err_many; fi
        fi

        if [ "$dbcmd" = "put" ]; then
                if [ $counter -eq 4 ]; then dbkey="$4"; fi
                if [ $counter -eq 5 ]; then dbval="$5"; fi
                if [ $counter -ge 6 ]; then param_err_many; fi
        fi

        if [ "$dbcmd" = "new" ]; then
                if [ $counter -eq 4 ]; then param_err_many; fi
        fi

        if [ "$dbcmd" = "list" ]; then
                if [ $counter -eq 4 ]; then param_err_many; fi
        fi
done

The output I get is as follows...

$ source db-scripts/sitedb.bash del john thirdtest
running command del
entering delete param check 1
entering delete param check 2
entering delete param check 3
bash: [: =: unary operator expected
error: parameter missing

I really just need an extra set of eyes, because everything seems fine with the if statement in question.

Answer 1

There's a moderate chance the problem is one of the many lines similar to:

if [ $counter -eq 4 ]; then param_err_many; fi

The fix will be to enclose the variable in double quotes — "$counter", or to initialize the counter to 0 instead of the empty string.

If that does not solve the problem, then you should include the debug output from running bash -x yourscript.sh around the point where the error occurs in your question. In fact, in future, if something misbehaves in the shell, the first thing to do is run it with bash -x to see what is going wrong.