Didn't know about look. Seems good enough (tested on a HDD): $ dd of=pwned-passwords-sha1-ordered-by-hash-v5.txt oflag=nocache conv=notrunc,fdatasync count

Didn't know about look. Seems good enough (tested on a HDD): $ dd of=pwned-passwords-sha1-ordered-by-hash-v5.txt oflag=nocache conv=notrunc,fdatasync count=0 0+0 records in 0+0 records out 0 bytes (0 B) copied, 9.5864e-05 s, 0.0 kB/s $ time look `sha1sum <(echo -n password) | tr [a-z] [A-Z] | cut -d" " -f1` pwned-passwords-sha1-ordered-by-hash-v5.txt 5BAA61E4C9B93F3F0682250B6CF8331B7EE68FD8:3730471 real 0m0.137s user 0m0.002s sys 0m0.013s dd is used to drop the file from the fs cache. Something the author probably didn't do given the unrealistic 49μs. It's simply not possible to fetch data from a HDD that fast.