Remove the first n characters from the file content.

remove-bom.zsh

#!/usr/bin/env zsh
# Reference:
# https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html

display_help() {
  cat <<EOF

*** Remove the first n characters from the file content. ***
    Use me when dos2unix nor nkf doesn't work.

EOF
}

main() {
  [[ "$1" == '--help' ]] && display_help
  # Input
  printf "\033[93mTarget file? >> \033[0m"
  read -r file_in
  [[ ! -f "$file_in" ]] && printf "\033[31mFile not found\033[0m" && return 1
  printf "\033[93mNumber of chars to be removed? >> \033[0m"
  read -r num

  # Preparation
  stem="${file_in%.*}"
  suffix="${file_in##*.}"
  file_out="$stem"_precessed."$suffix"
  str_out=$(sed -r 1s/^.{"$num"}//g "$file_in")

  # Confirm
  printf "\033[93mTest output: \033[0m%s" "$str_out" | head -c 64
  printf "\n\033[93mOK? (Y/n) >> \033[0m"
  read -r res

  # Execute
  if [[ "$res" == [Yy] ]]; then
    echo "$str_out" > "$file_out"
    printf "\033[93mSaved:\033[0m %s\n" "$file_out"
  else
    printf "\033[31mExited\033[0m\n"
  fi
}

main "$@"