Rotate an image either from a local file or a URL

rotate-img

#!/usr/bin/env bash

# Rotates an image from either a local file or from a URL passed on the command line or to stdin,
# and prints the rotated image file path to stdout.
#
# Positive angles rotate clockwise, negative counterclockwise.

# Exit on first error
set -e

validfile() { [[ -r ${1} ]]; }

validurl ()
{
  # Read the first byte from the URL
  if curl --output /dev/null  --silent --fail -r 0-0 "${1}"; then
     return 0
  else
     return 1
  fi
}

installed () { command -v "${1}" >/dev/null 2>&1 || { >&2 echo "Cannot execute the ${1} command"; exit 1; } }

installed convert # From Imagemagick
installed curl

output_file=
angle="90" # Default to rotating 90 degrees clockwise

while [[ $# != 0 ]]; do
   case "${1}" in
      -d|--degrees|--degree|-a|--angle)
         angle="${2}"
         shift 2
         ;;
      -o|--output)
         output_file="${2}"
         shift 2
         ;;         
      *)
         rotate_params+=("${1}")
         shift
         ;;
   esac
done

# Get the file path or URL from the command line argument or from stdin.
[[ ${#rotate_params[@]} -ge 1 ]] && input="${rotate_params[*]}" || input=$(cat)

if [[ -z ${input} ]]; then
   >&2 echo "No file or URL was provided"
   exit 1
fi

img_file=

if validfile "${input}"; then
  img_file="${input}"
elif validurl "${input}"; then
  tmpfile=$(mktemp /tmp/flip-img-XXXXXX)
  curl --output "${tmpfile}" --silent "${input}"

  # Add a file extension to the tmp file so the output file has the extension too.
  ext=$(grep "$(file -b --mime-type "${tmpfile}")" /etc/mime.types | awk '{print $2}')
  if [[ ! -z ${ext} ]]; then
    mv "${tmpfile}" "${tmpfile}.${ext}"
    tmpfile="${tmpfile}.${ext}"
  fi

  # Remove the tmp file when we're done.
  trap 'rm -f ${tmpfile}' EXIT INT 

  img_file="${tmpfile}"
else
  >&2 echo "${input} cannot be read"
  exit 1
fi

if [[ -z ${output_file} ]]; then
   output_file=$(echo "${img_file}" | sed -E "s|(.*)(\..*)|\1_rotated\2|")
fi

convert -rotate "${angle}"  "${img_file}" "${output_file}"

if [[ -r ${output_file} ]]; then
   echo "${output_file}"
   exit 0
else
   >&2 echo "${output_file} was not created"
   exit 1
fi