Take a look at the command "mogrify".  It's a command that comes with imagmagic (convert) and generally takes the same options as convert, but it made to do bulk converstion, so that you don't need to have a for loop around your command.
Just be aware that it will usually replace your images with the converted versions, so make sure you test things out on backups.

Brian Cluff

On 12/31/2015 02:34 PM, Matt Graham wrote:

On Dec 31, 2015 1:57 PM, "Michael Havens" <bmike1@gmail.com> wrote:

Is there a way to scale a bunch of pictures down to the same size
with GIMP?

Probably, but it'd be a lot more of a pain to do that than to do what
sean suggested.

On 2015-12-31 14:07, sean wrote:

Use ImageMagick instead - it's designed for this and is quite powerful.

To expand on what sean wrote:

for FILE in *.jpg ; do
    NEWFILE=`echo "$FILE" | sed -e 's/.jpg$/_resized.jpg/'`
    convert "$FILE" -resize 50% "$NEWFILE"
    done

...will take all the .jpg files in the current dir and write out new
files named (original filename)_resized.jpg which have their X and Y
dimensions reduced by 50%.  The original files will still be there.  The
geometry specification in ImageMagick is powerful, so it's more
complicated than you may expect.
http://www.imagemagick.org/script/command-line-processing.php#geometry
for all the things you can do with it.

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