Script to make a PDF look like it was scanned

looks_like_scanned.sh

#!/usr/bin/env bash
# shellcheck disable=SC2128
SOURCED=false && [ "$0" = "$BASH_SOURCE" ] || SOURCED=true

if ! $SOURCED; then
  set -euo pipefail
  IFS=$'\n\t'
fi

#################### help
function short_usage() {
  (>&2 echo \
"Usage:
  $(basename "$0") [options] <input_file>")
}

function usage() {
  (>&2 short_usage )
  (>&2 echo \
"
Make a PDF look like scanned.

Arguments:
  input_file    Username of the new user to add.

Options:
  -d                    Enable debug output.
  -o OUTPUT_FILE        Ouput file name [default: output.pdf]
  -h                    Show this help and exits.

Example:
  $(basename "$0") input.pdf
")
}

debug=false
help_flag=false
output_file='output.pdf'

while getopts ":do:h" opt; do
  case $opt in
    d)
      debug=true
      ;;
    o)
      output_file="$OPTARG"
      ;;
    h)
      help_flag=true
      ;;
    \?)
      (>&2 echo "Error. Invalid option: -$OPTARG")
      exit 1
      ;;
    :)
      (>&2 echo "Error.Option -$OPTARG requires an argument.")
      exit 1
      ;;
  esac
done

if $help_flag; then
  usage
  exit 0
fi
#################### end: help

#################### utils
if $debug; then
  function echodebug() {
    (>&2 echo -en "[$(date '+%F %H:%M:%S')][debug]: ")
    (>&2 echo "$@" 1>&2)
  }
else
  function echodebug() { true; }
fi
#################### end: utils

# Shell Script: is mixing getopts with positional parameters possible?
# https://stackoverflow.com/q/11742996/2377454
numopt="$#"
echodebug "numopt: $numopt"
echodebug "OPTIND: $OPTIND"

# parameter not specified
if (( numopt-OPTIND < 0 )) ; then
  (>&2 echo "Error: parameter <input_file> is required.")
  short_usage
  exit 1
fi

# unrecognized extra parameters not specified
if (( numopt-OPTIND > 0 )) ; then
  (>&2 echo "Error: unrecognized extra parameters specified.")
  short_usage
  exit 1
fi

input_file="${*:$OPTIND:1}"

echodebug "Arguments:"
echodebug "  * input_file: $input_file"
echodebug
echodebug "Options:"
echodebug "  * debug (-d): $debug"
echodebug "  * output_file (-o): $output_file"

# Source:
#   https://gist.github.com/andyrbell/25c8632e15d17c83a54602f6acde2724
#
# use ImageMagick convert
# the order is important. the density argument applies to input.pdf and
# resize and rotate to output.pdf
convert -density 90 \
        "$input_file" \
        -rotate 0.5 -attenuate 0.2 +noise Multiplicative -colorspace Gray \
        "$output_file"

 exit 0