linux sha1sum

Print or check SHA1 (160-bit) checksums. With no FILE, or when FILE is -, read standard input.

sha1sum {file}

If you want to send the file together with its sha1sum output redirect the output to a file:

sha1sum {file} > {file}.sha1

Send both files and the other party can do a…

sha1sum -c {file}.sha1

It should show OK if the sha1 is correct.