Shell Script examples for user Input. Part6

Handling User Inputs from the shell - Code snippets

1.  Grab all parameters
  
    count=1
    echo "No of parameters = ${!#}"
    while [ $count -le $#]
    do
      echo "param[$count] = ${$count}"
      count=$[$count+1]
    done
   
    But this does not work well when no of command line parameters exceeds 9.

2.  Grab all parameters
   
    count=1
    for var in $*
    do
      echo "Param[$count] = $var"
      count=$[$count+1]
    done
 
    count=1
    for var in $@
    do
      echo "param[$count] = $var"
      count=$[$count+1]
    done
 
    Using this with
    file a b c d1
 
    will produce
    Param[1] = a
    param[1] = a
    param[2] = b
    param[3] = c
    param[4] = d1
   
    For explanation look HERE.


3.  Use of shift to process parameters

    count=1
    while [ -n "$1" ]
    do
      echo "param[$count]: $1"
      count=$[$count + 1]
      shift
    done
   
    For explanation look HERE.

4.  Using shift to process options and parameters

    Suppose your code expects options a,b(with 2 parameters), c, d and a set of parameters.
   
    count=1
    while [ -n "$1" ]
    do
      case "$1" in
      -a) echo "Found -a option";;
      -b) echo "Found -b option with value $2 and $3"
          shift 2;;       # since we know we have consumed 3 values from the list of parameters.We shift one at the end of each iteration
      -c) echo "Found -c option";;
      -d) echo "Found -d option";;
      --) shift           # We use the -- separator to delineate options from parameter set
          break;;
      *)  echo "$1 not an option";;
      esac
      shift     # this is for whatever option we might have found, we need to shift them out
    done
 
    count=1
    for param in "$@"     # now only params remain
    do
      echo "Param[$count] = $param"
      count=$[$count + 1]
    done
   
    The dependency on the "--" is the only drawback of this method.
    For explanation look HERE.

5.  using getopt to process parameters

    set -- `getopt ab:c:d "$@"`
    while [ -n "$1" ]
    do
      case "$1" in
        -a) echo "Found -a option" ;;
        -b) echo "Found -b option with parameter $2"
            shift ;;
        -c) echo "Found -c option with parameter $2"
            shift;;
        -d) echo "Found -d option";;
        --) shift
        break;      #this character means options have ended
        *)  echo "Not supported option $1";;
      esac
      shift
    done
 
    count=1
    for param in "$@"     # now only params remain
    do
      echo "Param[$count] = $param"
      count=$[$count + 1]
    done
   
    For explanation look HERE.
    But this fails when the parameters have spaces in them.

6.  using getopts to process parameters.

    count=1
    while getopts ab:c:d opt
    do
      case "$opt" in
        -a) echo "Found -a option" ;;
        -b) echo "Found -b option with parameter $OPTARG";;
        -c) echo "Found -c option with parameter $OPTARG";;
        -d) echo "Found -d option";;
        *)  echo "Found unknown option $opt";;
      esac
    done
 
    shift $[ $OPTIND - 1 ]
 
    count=1
    for param in "$@"     # now only params remain
    do
      echo "Param[$count] = $param"
      count=$[$count + 1]
    done
   
    For explanation look HERE.