Extract positional parameters without modifying (the number of) command line arguments ($# and $@).

# See:
# - http://tldp.org/LDP/abs/html/string-manipulation.html#AEN5117
# - http://tldp.org/LDP/abs/html/internalvariables.html#POSPARAMREF
# - http://tldp.org/LDP/abs/html/internalvariables.html#IFSREF
# - http://tldp.org/LDP/abs/html/parameter-substitution.html#PARAMSUBREF
# - cmdparser, http://codesnippets.joyent.com/posts/show/1697

export IFS=$' \t\n'

# create a fake command line
set -- "First one" "second" "third:one" "" "Fifth: :one"
set -- "First one" "second" "third:"$'\n'"one" "" "Fifth: :one"

echo $#                             # number of arguments

printf "%s\n" "${@}"                # all arguments         

printf "%s\n" "${1}"                # first argument          
printf "%s\n" "${3}"                # third argument
printf "%s\n" "${5}"                # last argument

printf "%s\n" "${@:1}"              # all arguments starting with the first
printf "%s\n" "${@:2}"              # all arguments starting with the second
printf "%s\n" "${@:3}"              # all arguments starting with the third

printf "%s\n" "${@:(-$#):1}"        # first argument          
printf "%s\n" "${@:$#:1}"           # last argument          
printf "%s\n" "${!#}"               # last argument

printf "%s\n" "${@:1:1}"            # first argument
printf "%s\n" "${@:3:1}"            # third argument
printf "%s\n" "${@:5:1}"            # fifth argument
printf "%s\n" "${@:(-1):1}"         # last argument
printf "%s\n" "${@:(-2):1}"         # second-to-last argument



# process one positional parameter at a time without modifying $# or $@
for (( i=1; i <= $#; i++ )); do printf "%s\n" "${@:${i}:1}"; done

echo $#    # 5


# $# and $@ get modified
for (( i=1; i <= $#; i++ )); do echo $i; printf "%s\n" "$1"; shift; done

echo $#   # 2


set -- "First one" "second" "third:"$'\n'"one" "" "Fifth: :one"

# $# and $@ get modified
while [[ $# -gt 0 ]]; do printf "%s\n" "$1"; shift; done

echo $#   # 0