Fix name of images in Magento whose names only vary by case (renaming them both in the filesystem and the database catalog). This is useful if media files need to pass through a case-insensitive filesystem, like a Mac.

fix-diffcase-images.sh

#!/bin/bash

# Settings
SUFFIX=alt
MAGERUNCMD=magerun

# Sanity Checks
type $MAGERUNCMD >/dev/null 2>&1 || {
    echo "ERROR: This script requires the command '$MAGERUNCMD' to be executable in the current path."
    exit
}
[[ "$PWD" == *media/catalog/product ]] || {
    echo "ERROR: This script should be run from the 'media/catalog/product' directory of your Magento install."
    exit
}

# Directions
echo "It is highly recommended that you run the 'media:images:removeorphans' magerun extension before this."
echo '---'

if [ ! "$1" = '-f' ]; then
    echo 'This script performs a dry run by default. To force changes pass flag -f.'
    read -p "Press [Enter] key to continue with dry run or [Ctrl-C] to exit..."
else
    echo 'WARNING: Forcing updates. Changes are destructive and cannot be undone.'
    read -p "Press [Enter] key to continue with force mode or [Ctrl-C] to exit..."
fi
echo '---'

# Work Time
DUPLICATES=$(find . -path ./cache -prune -o -type f)
echo "$DUPLICATES" | sort -f | uniq -id | while read -r FILENAME; do
    INDEX=1
    while read OLD_FILENAME; do
        NEW_FILENAME=$(echo "$OLD_FILENAME" | tr '[:upper:]' '[:lower:]' | perl -pe "s/\.([^.]*)\$/_$SUFFIX$INDEX.\1/")

        if [ ! -e "$NEW_FILENAME" ]; then
            eval $MAGERUNCMD db:query $([ ! "$1" = '-f' ] && printf -- --only-command) \
                "'UPDATE mag_catalog_product_entity_media_gallery SET value = \"${NEW_FILENAME#.}\" WHERE BINARY value = \"${OLD_FILENAME#.}\";'" \
                && eval $([ ! "$1" = '-f' ] && printf echo) mkdir -p "${NEW_FILENAME%/*}" \
                && eval $([ ! "$1" = '-f' ] && printf echo) mv -n "$OLD_FILENAME" "$NEW_FILENAME"
        else
            echo "New name $NEW_FILENAME for $OLD_FILENAME already exists. Refusing to move or update DB."
            false
        fi

        if [ $? -gt 0 ]; then
            echo 'Terminating early on fatal error.'
            [ "$1" = '-f' ] && echo 'Error above may need to be manually fixed.'
            exit
        fi
        
        echo "Moved $OLD_FILENAME => $NEW_FILENAME."
        
        ((INDEX++))
    done < <(grep -i "$FILENAME" <<< "$DUPLICATES")
done

What you're describing now (a script that you want people to edit, i.e. by setting MAGERUNCMD to a different value inline) is really an antipattern. If you want to support multiple names for the same command, just enumerate which ones you support. There aren't that many likely names for this command - it's going to be one of {n98-,}magerun{,.phar}.

1. I'd recommend parameterizing that, or just picking the first executable on PATH that matches one of those names.
2. I'd recommend not letting anyone modify the script for one-off executions, which is what you seem to be describing, IIUC.