Select index of a particular named argument

nth.sh

function nth() {
  target=$1
  shift
  idx=1
  for symbol in $@; do
    if [ $symbol == $target ]; then
      echo $idx
      return
    fi
    idx=$(($idx+1))
  done
}

# Example:
# nth b a b c
# -> 2
# 
# Useful for, e.g., cut 
# cut -f $(nth fieldofinterest $(head f.txt)) f.txt