UPDATE: I’ve since been told an even better way.

I script as much as possible for Rubenerd, including image processing. This is how I’ve been concatenating images side by side for the longest time:

$ montage -border 0             \
    -geometry x$_ORIGINALHEIGHT \
    -tile 2x                    \
    $_IMAGE1 $_IMAGE2           \

But there’s an easier way!

$ montage -mode concatenate $_IMAGE1 $_IMG2 $_OUT

I don’t have an install to try in GraphicsMagick, but my hunch is its ImageMagick-specific.

More code or lines in your scripts are rewarding, but not half as much as being able to take lines out.