Pipe multiple files from curl to other program

feh will not be able to distinguish between several images sent on its standard input, unless some kind of "protocol" is implemented.

If you don't want to use temporary files, you could maybe use a loop:

for url in 'url1' 'url2'; do
    curl -skb token "$url" | feh -
done

This will download and display each image one after the other. If you'd rather have several viewers opened at the "same time", add a little ampersand to it:

for url in 'url1' 'url2'; do
    (curl -skb token "$url" | feh - &)
done

Note that you can put everything on a single line, or maybe define a function:

$ for url in 'url1' 'url2'; do curl -skb token "$url" | feh -; done
$ for url in 'url1' 'url2'; do (curl -skb token "$url" | feh - &); done

function feh_urls
{
    for url; do
        curl -skb token "$url" | feh -
    done
}

$ feh_urls 'url1' 'url2'

Be careful with your quotes, as there may be some annoying spaces in your URLs or paths (... and I hope I didn't make such a mistake in the above examples...). If you go for a function, maybe add it to your .bashrc so you can use it in your shell without redefining it manually everytime.

For the sake of completeness, here is a little script (which could be made a function of course) involving some temporary files, saving a few curl and feh processes on the way. I am using wget instead of curl because depending on your version, you might not be able to grab remote filenames properly (you could give your images different names of course).

#!/bin/bash

img_dir=$(mktemp -d)
cd $img_dir
wget -q --no-check-certificate --load-cookie token "$@"
feh $img_dir/*
rm -r $img_dir

Usage:

$ ./feh_urls.sh 'url1' 'url2'

Note that the advantage here is that feh doesn't get spawned several times, and can load all the images at once (use the arrow keys to browse them).

You might also be interested in this page if you want more information about cookie management with wget, or this page for details about the SSL/TLS options.