Command line arguments in Bash [duplicate]

I want to write a bash script which takes different arguments. It should be used like normal linux console programs:

my_bash_script -p 2 -l 5 -t 20

So the value 2 should be saved in a variable called pages and the parameter l should be saved in a variable called length and the value 20 should be saved in a variable time.

What is the best way to do this?

Use the getopts builtin:
here's a tutorial

pages=  length=  time=

while getopts p:l:t: opt; do
  case $opt in
  p)
      pages=$OPTARG
      ;;
  l)
      length=$OPTARG
      ;;
  t)
      time=$OPTARG
      ;;
  esac
done

shift $((OPTIND - 1))

shift $((OPTIND - 1)) shifts the command line parameters so that you can access possible arguments to your script, i.e. $1, $2, ...

Something along the lines of

pages=
length=
time=

while test $# -gt 0
do
    case $1 in
        -p)
            pages=$2
            shift
            ;;
        -l)
            length=$2
            shift
            ;;
        -t)
            time=$2
            shift
            ;;
        *)
            echo >&2 "Invalid argument: $1"
            ;;
    esac
    shift
done