til/unix/get-the-sha256-hash-for-a-file.md

Get The SHA256 Hash For A File

Unix systems come with a sha256sum utility that we can use to compute the SHA256 hash of a file. This means the contents of file are compressed into a 256-bit digest.

Here I use it on a SQL migration file that I've generated.

$ sha256sum migrations/0001_large_doctor_spectrum.sql
b75e61451e2ce37d831608b1bc9231bf3af09e0ab54bf169be117de9d4ff6805  migrations/0001_large_doctor_spectrum.sql

Each file passed to this utility gets output to a separate line which is why we see the filename next to the hash. Since I am only running it on a single file and I may want to pipe the output to some other program, I can clip off just the part I need.

sha256sum migrations/0001_large_doctor_spectrum.sql | cut -d ' ' -f 1
b75e61451e2ce37d831608b1bc9231bf3af09e0ab54bf169be117de9d4ff6805

We can also produce these digests with openssl:

$ openssl dgst -sha256 migrations/0001_large_doctor_spectrum.sql
SHA2-256(migrations/0001_large_doctor_spectrum.sql)= b75e61451e2ce37d831608b1bc9231bf3af09e0ab54bf169be117de9d4ff6805

$ openssl dgst -sha256 migrations/0001_large_doctor_spectrum.sql | cut -d ' ' -f 2
b75e61451e2ce37d831608b1bc9231bf3af09e0ab54bf169be117de9d4ff6805

See sha256sum --help or openssl dgst --help for more details.