dd can do it on an existing file or stream, transforming sequences of 0 it contains into "holes".

caveat operator: to ensure the conv=sparse operand achieves the desired outcome, be sure to use an output blocksize equal to st_blksize of the output filesystem.

or just use `cp --sparse=always` if it's from one file to another

That is not so portable, so I recommend sticking with dd.

Yup, `dd` helps in a lot of situations when you need portability, not just this one.

Commands like `cp --sparse=always` aren't worth such a blanket disrecommendation though; if you are working directly at a console as opposed to scripting you typically don't need portability.

Again, most of the consoles I work at don’t use GNU coretools.

Then you obviously can't use this, but many people reading my suggestion can.