#!/bin/sh

if [ $# -ne 2 ] || [ "$1" = "-h" ] ; then
    cat<<EOF
Usage: ${1##*/} FILE1 FILE2

Swap 2 filenames around.

EOF

    exit
fi

## We need a temp file is case both files are in the same folder. We use the
## unsecure option since we do not want to create a empty file in
## advance. Indeed, creating a file with mktemp is problematic for folders since
## non-GNU mv can only move _into_ an exisintg folder. But we do not overwrite
## if file exists.
TEMPFILE="$(mktemp -u "$1.XXXXXX")"

case "$1" in
	*/*) DIR1="${1%/*}" ;;
	*) DIR1="." ;;
esac
case "$2" in
	*/*) DIR2="${2%/*}" ;;
	*) DIR2="." ;;
esac

if ! mv -n "$1" "$TEMPFILE"; then
    echo >&2 "Race condition, exiting. Try again."
fi
mv -n "$2" "$DIR2/${1##*/}"
mv -n "$TEMPFILE" "$DIR1/${2##*/}"