Flexible number of parameters in a bash script

Question

I am using the following kind of bash code. I store some information within log file which name is defined in the bash script.

LOGNAME="/tmp/ETH"
LOG_FILE="${LOGNAME}.log"    

function exit_error()
{
    case "$1" in
        100 )
            echo "Bad arguments supplied - Enter help"
            echo "Bad arguments supplied - Enter help" >> "${LOG_FILE}"
            ;;      
        101 )
            echo "Illegal number of parameters"
            echo "Illegal number of parameters" >> "${LOG_FILE}"
            ;;       
        * )
            ;;
    esac    
    exit 1;
}

function current_status()
{
    INT_STATUS=$(cat /sys/class/net/eth1/operstate)
    echo "status : $INT_STATUS"
    echo "status : $INT_STATUS" >> "${LOG_FILE}"
}

function connect_eth()
{
    ...
}

...

case "$1" in
    current_status )
        if [ "$#" -ne 1 ]
        then
            exit_error 101
        else
            current_status
        fi
        ;;  
    connect_eth )
        if [ "$#" -ne 1 ]
        then
            exit_error 101
        else
            connect_eth
        fi
        ;;
    read_MAC_addr )
        if [ "$#" -ne 1 ]
        then
            exit_error 101
        else
            read_MAC_addr 
        fi      
        ;;  
    read_IP_addr )
        if [ "$#" -ne 1 ]
        then
            exit_error 101
        else
            read_IP_addr
        fi
        ;;
    * )
        exit_error 100
        ;;
esac
exit 0;

I would like to modify the script in order to use the specified log name if no other log name is specified as last parameter. However, I would like to keep my "exit_error 101" in switch case which is based on the number of parameters passed to the script. Is there a way to do that ? Because I can not modify the $# variable.

tgo · Accepted Answer · 2015-02-27 12:54:54Z

2

It should be possible. Do something like this:

CMD="$1"
shift
# use provided logname or set to default if not found
LOGNAME="${1:-/tmp/ETH}
shift
LOGFILE="${LOGNAME}.log"
# now, since we shifted, you just have to check for $# -eq 0 to
# be sure there are no params left.

... your function definitions here ...

# exit 101 if there are some parameters left
if [ $# -ne 0 ]; then
  exit_error 101
fi

case "$CMD" in
  current_status)
    current_status
    ;;
  ...
  *)
    exit_error 100
    ;;
esac

If you want more flexibility, you can always use getopts and named parameters. It is usually much easier to maintain.

And, if I were you, I would also centralize error handling before the case statement to avoir repeating the same check everywhere.

edited Feb 27, 2015 at 12:54

answered Feb 27, 2015 at 12:24

tgo

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4 Comments

ogs Over a year ago

I have already tried your solution, I pass thru exit_error 100 everytime.. because after shift $1 is equal to nothing

tgo Over a year ago

I completed the sample. Obviously $1, will be empty and $# equal to zero in non error cases. That was the point. Thus you have to use $CMD.

ogs Over a year ago

Thank tgo it works ! But your solution works only if one parameter is gave to the functions, is not ? If I have n function which accept variable parameters, I have to use an a switch case, based on each posibilities, on top of the script or there is a quite simple and efficient solution ?

tgo Over a year ago

@SnP you are welcome. Yes, this way things can grow quite complex indeed. That's why I was referencing getopts. And if, with getopts, things get too complex, it might mean you need more than one script/command.

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