How do I do an N-way diff?

The tool to do this is Diffuse. It is also generally available from repos (at least in Debian and Arch, where I checked). It works as you would expect it to:

 diffuse file1 file2 file3 file4 

and so on.

The fdupes tool may be of some use to you here (should be in the repositories). If you have a large number of files to compare, you can use it to reduce the work you have to do by identifying which ones are already identical. As noted below, it only works with directory arguments. If you have all the files to diff in one directory you can do something like:

fdupes . 

To identify files which are the same. Or:

comm -13 <(fdupes . |sort -u) <(find . -maxdepth 1 | sort) 

To identify files which are unique.

The diff3 command may also be useful.

If you only want to see if the files agree, then you don't really need diff. Just use sha1sum or something like that.

for instance:

#!/bin/sh command="foo;bar|baz" for server in server1 server2 server3 server4 server5 server6: do echo $server $(ssh $server "$command" |sha1sum) done | sort -k2 

This will give you a space-separated list of server,sha1sum pairs. Servers with the same sha1sum have the same output:

server1 55ca6286e3e4f4fba5d0448333fa99fc5a404a73 *- server3 55ca6286e3e4f4fba5d0448333fa99fc5a404a73 *- server6 55ca6286e3e4f4fba5d0448333fa99fc5a404a73 *- server2 d961c3de6d6c99429806ae3d6d03f316a1168ac6 *- server4 d961c3de6d6c99429806ae3d6d03f316a1168ac6 *- server5 dcdc24e139db869eb059c9355c89c382de15b987 *- 

You can do further processing to get a list of matching servers, for example:

#!/bin/sh command="foo;bar|baz" for server in server1 server2 server3 server4 server5: do echo $server $(ssh $server "$command" |sha1sum) done | sort -k2 | while read srv sum; do if [ "$prevsum" == "$sum" ]; then echo -n " " else echo fi echo -n $srv prevsum=$sum done 

which gives output such as:

server1 server3 server6 server2 server4 server5