Identify how similar a file is to each file in a group of others.

similarities.sh

#!/bin/bash

fileA="$1"
shift
for fileB in "$@"; do
    (
        # diff once grep twice with the help of tee and stderr
        diff $fileA $fileB | \
            tee >(grep -cE '^< ' >&2) | \
                  grep -cE '^> ' >&2
    # recapture stderr
    ) 2>&1 | (
        read -d '' diffA diffB;
        printf "The files %s and %s have %s:%s diffs out of %s:%s lines.\n" \
            $fileA $fileB $diffA $diffB $(wc -l < $fileA) $(wc -l < $fileB)
    )
done | column -t