Horizontally flip an image from a local file or a URL

flip-img

#!/usr/bin/env bash

# Flips an image horizontally from either a local file or from a URL passed on the command line or to stdin,
# and prints flipped image file path to stdout.
#
# Options:
#
# -h,--help       Display help
# -z,--horizontal Flip the image horizontally (default)
# -i,--input      The image to flip
# -o,--output     The file to output to
#
# Examples:
#
# flip-img -i ./input.png -o ./output.png
#

# Exit on first error
set -e

# Debug
#set -x

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

# Checks that a file is valid
validfile() { [[ -r ${1} ]]; }

# Checks if a variable is empty
empty () { [[ -z $1 ]]; }

# Checks that a URL is valid (attempts to fetch it)
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
}


help () {
    scriptName=$(basename "$0")
    echo "$scriptName [options]"
    echo
    echo Options:
    echo
    echo "--help, -h        Prints this help menu"
    echo "--input, -i       The file or URL for the image to flip"
    echo "--output, -o      The image file to create"
    echo "--horizontal, -z  Flip horizontally (default)"
    echo "--vertical, -v    Flip vertically"
    echo
    echo Example:
    echo
    echo
    echo "$scriptName" --input "./input.gif" --output "./output.gif" --horizontal
    echo
}

installed convert # From Imagemagick
installed curl

outputFile=
flipOrFlop="-flop" # Default to flipping it horizontally

if [[ $# = 0 ]]; then
    help
    exit 1
fi

while [[ $# != 0 ]]; do
    case "${1}" in
        -h|--help)
            help
            exit 0
            ;;
        -i|--input)
            input="$2"
            shift 2
            ;;
        -o|--output)
            outputFile="${2}"
            shift 2
            ;;
        -v|--vertical)
            flipOrFlop="-flip"
            shift
            ;;
        -z|--horizontal)
            flipOrFlop="-flop"
            shift
            ;;
        *)
            shift
            ;;
    esac
done

# Accept input name on stdin too
if [[ -z $input ]]; then
    input=$(cat)
fi

# Check the parameters
if [[ -z $input ]]; then
    >&2 echo "No file or URL was provided"
    exit 1
fi

imgFile=

if validfile "${input}"; then
  imgFile="${input}"
elif validurl "${input}"; then
  tmpfile=$(mktemp /tmp/flip-img-XXXXXX)
  curl --location --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 [[ -n ${ext} ]]; then
    mv "${tmpfile}" "${tmpfile}.${ext}"
    tmpfile="${tmpfile}.${ext}"
  fi

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

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

if empty "$outputFile"; then
    outputFile=$(echo "${imgFile}" | sed -E "s|(.*)(\..*)|\1_flipped\2|")
fi

convert "${flipOrFlop}" "${imgFile}" "${outputFile}"

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