bash - "[: too many arguments" error in a while loop after an if

Question

First: I'm fairly new to bash batch-scripting but have experience in other script and programming languages

Second: I already looked at Meaning of "[: too many arguments" error from if[] (square brackets) but this that was not the solution for my problem.

I'm creating a command-line parser in a bash script. My first attempt actually already works but still has some if-statement code-duplication in the main-loop which I want to solve, so I moved it to the actual parsing-function and then I run into a "[: too many arguments" error which I cannot get solved (adding "" around variables did not work) in a piece of code which does work if I do not move the if.

Note: in the actual code there is one more command-line option, I left that out for 2 reasons:

1. shorter listing
2. error is seen on all options

The working code looks like this:

    arg_str = $@
    args=("$@")
    arglen=$#

    target=some_filename.txt
    in_dir=/some_input_dir/

    function working_parser()
    {
        local option=$1
        myresult=''

        i=0

        while [ ${args[i]} != $option -a $i -n $arglen ]
        do
            i=$((i+1))
        done
        #TODO add check on $i>arglen
        myresult=${args[$((i+1))]}
    }

    if [[ $arg_str == *'-t'* ]]; then
        working_function '-t'
    fi
    if [[ $myresult != '' ]]; then
        target=$myresult
    fi


    if [[ $arg_str == *'-i'* ]]; then
        working_function '-i'
    fi
    if [[ $myresult != '' ]]; then
        in_dir=$myresult
    fi

The failing code looks like this (Left out the definitions, since they are the same as for the working code). The '[: too many arguments' error occurs in the while loop, where it did not happen in that same code in the working-version.

    function failing_parser()
    {
        local option=$1
        myresult=''

        if [[ $arg_str == *$option* ]]; then
            i=0

            while [ ${args[i]} != $option -a $i -n $arglen ]
            do
                i=$((i+1))
            done
            #TODO add check on $i>arglen
            myresult=${args[$((i+1))]}
        fi
    }

    failing_parser '-t'
    if [[ $myresult != '' ]]; then
        target=$myresult
    fi

    failing_parser '-i'   
    if [[ $myresult != '' ]]; then
        in_dir=$myresult
    fi

What am I doing wrong?

Answer 1

There are too many arguments because -n is unary operator, not a binary operator. Perhaps you mean -ne?

while [ "${args[i]}" != "$option" -a "$i" -ne "$arglen" ]

-a is considered nonportable and obsolete; it's better to use two separate [ commands joined by && instead:

while [ "${args[i]}" != "$option" ] && [ "$i" -ne "$arglen" ]

However, since you are already using one bash-specific feature (arrays), you may as well use [[ ... ]] as well:

while [[ "${args[i]}" != "$option" && "$i" -ne "$arglen" ]]

or even an arithmetic command:

while [[ "${args[i]}" != "$option" ]] && (( i != arglen ));