diff-all-first-vs-second

#!/bin/bash

die() { printf %s "${@+$@$'\n'}" 1>&2 ; exit 1 ; }
see() ( { set -x; } 2>/dev/null ; "$@" )

# diff all files in first ($1) against their counterpart in second ($2).  Files that exist only in second are ignored.
# nonrecursive!!!

[ $# -eq 2 ]                    || die "need 2 arguments: both dirnames"
first="$1"  ; test -d "$first"  || die "first dirname argument is not a dir: $first"
second="$2" ; test -n "$second" || die "second dirname argument is not a dir: $second"

for file in "$first"*; do
    if [ -f "$file" ]; then
        filename=$(basename "$file")
        # echo "Comparing $filename:"  # diff --help
        if diff -U0 "$file" "$second/$filename"; then
           echo "same: $file $second/$filename"
        fi
    fi
done