A script I use to (bulk) resize images to a largest dimension of 1080px, which I use for my blog.

blog-resizer.sh

#!/bin/bash

#Fundamentals
ALLMODE=0

# Get parameter
if [ -z "$1" ]; then
    echo Filename or -all flag needed
    exit 1
elif [ "$1" == "-all" ]; then
    ALLMODE=1
    echo "Blog-resizer - resizing all images in directory"
else
    NAME=$1
fi

# Set up filename array
if [ $ALLMODE == 1 ]; then
    names=$(ls)
else
    names=( $NAME )
fi

# Loop over files
for f in $names
do
# File existence test
    if [ ! -f "$f" ]; then
        echo "File $f does not exist or is not a file"
        exit 1
    fi

# Split the input name into an array
    IFS="." read -a splitname <<< "${f}"

# Set operational variables
    newname=""
    num=${#splitname[@]}
    let num-=1
    length=$num

# Get name of new file
    for l in ${splitname[@]}
    do
        if [ $num == 0 ]; then
            newname+="_e"
        fi
        if [ $num != $length ]; then
            newname+="."
        fi
        newname+="$l"
        let num-=1
    done

# Tell the user
    echo "Resizing $f, as $newname (1080x1080)"

# Resize
    convert $f -resize 1080x1080 $newname

done