Bash script making bash scripts

#/bin/bash

# Define editor
editor=/usr/bin/vi

# read 2 first bytes
read_beggining () {
if [ -e $filename ] && [ $(wc -c $filename | awk -F" " '{ print $1 }') -ge 2 ]; then
  read -r -n 2 beggining < $filename
fi
}

# Function adds bash interpreter at the begining of file
add_bash () {
  # Check if file is zero-size. Sed doesn't work with empty files
  if [ -s $filename ]; then
    read_beggining
    if [ ! "$beggining"=="#!" ]; then
      sed -i '1i#!\/bin\/bash' $filename
    fi
  else
    # This will also create file if it deos not exist
    echo "#!/bin/bash" > $filename
  fi
}

# Check for option
if [ $# -eq 1 ]; then
  filename=$1
else
  option=$1
  filename=$2
  # Add interpreter declaration
  case $option in
    -b) add_bash
        exec=true
        ;;
    *)  ;;
  esac
  # If any option was used make file executable
  if [ $exec ] && [ ! -x $filename ]; then
    chmod +x $filename
  fi
fi


# Start editor function
start_vi () {
  $editor $filename
}

#Start editor
start_vi