When organising things like images and trying to avoid duplicates,
one pattern is to rename everything to `dirname_deadbeef0123.ext`
where the `deadbeef0123` is the first 12 hex digits of the sha256 sum.

In nushell this becomes
```nu
def hash_rename [
  stem = ""
  ] {
  let s = ( if $stem == "" { pwd | path basename } else { $stem } )
  let xs = $in
  if ( $xs | is-empty ) { ls *.* } else { $xs } | each { |x|
    let ifn = $x.name
    let ext = ( echo $ifn | path parse | get extension )
    let hash = ( sha256sum $ifn | str substring 0..11 )
    let ofn = $"($s)_($hash).($ext)"
    if ( $ofn | path exists ) {
      print $"($ofn) exists"
    } else {
      print $"($ifn) to ($ofn)"
      mv -v $ifn $ofn
    }
  }
}
```