.bakを再帰的につけるバックアップスクリプト

bak() (
    for file in "$@"; do
        bakfile="$file"'.bak'
        if [ -e "$bakfile" ]; then
            echo 'already exists: '"$bakfile"
            bak "$bakfile"
        fi
        cp "$file" "$bakfile"
    done
)

This is A.

$ ls
fileA
$ bak fileA
$ ls
fileA fileA.bak
$ echo 'This is A!' > fileA # fileAの中身を This is A! に上書き
$ bak fileA
already exists: fileA.bak
$ ls
fileA fileA.bak fileA.bak.bak