curatio.sh

#!/bin/bash
# See http://www.reddit.com/r/bash/comments/2xh32d/how_can_i_make_this_bash_script_better/
dirs=("16x10" "16x9" "5x4" "4x3");

# Fills in known ratios -> dirs in an associative array
declare -A ratios;
for r in "${dirs[@]}"; do
    ratios[$(echo $r | tr "x" "/" | bc -ql)]="$r"; # 1.77777... = 16x9
done;

mkdir -p "${dirs[@]}" "Others"; # Creates directories

shopt -s nocaseglob # Case insensitive glob
for file in *.{jpg,jpeg,gif,bmp,png}; do
    if [[ -f "$file" ]]; then # Check if file exists (prevents *.xxx in $file)
        # Current image ratio
        curRatio=$(identify -format "%w/%h" "$file" -quiet | bc -ql 2>&1);

        if [[ ! -z "$curRatio" ]] ; then
            # Move the file in the appropriate dir.
            if [ ${ratios[$curRatio]+_} ]; then  # Check if ratio exists
                mv "$file" "${ratios[$curRatio]}";
            else
                mv "$file" "Others/$file";
            fi;
        else
            echo "Got a problem with $file.";
        fi;
    fi;
done;

find "${dirs[@]}" "Others" -type d -empty -delete # Delete empty dirs

exit;

# ----------------------------------------------------------------------------
# https://www.reddit.com/r/bash/comments/2xh32d/how_can_i_make_this_bash_script_better/cp0ofc8 (iscfrc)

mkdir -p 16x10 16x9 5x4 4x3 Others

declare -A ratio_map=([160]=16x10 [177]=16x9 [125]=5x4 [133]=4x3)

find . -maxdepth 1 -type f -iregex '.*\.\(jpe?g\|gif\|png\|bmp\)$' -printf '%f\t' -exec identify -format '%[fx:(w/h)*100]' '{}' \; |
while IFS=$'\t' read -r file ratio; do
        [[ "${ratio_map[${ratio%%.*}]}" ]] && outdir=${ratio_map[${ratio%%.*}]} || outdir=Others
        mv -v "$file" $outdir
done

find . -maxdepth 1 -type d -regex '.*/\([0-9]+x[0-9]+\|Others\)$' -empty -print -delete