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.
wow, thanks, yet another tool to remember in the toolbox
sudo purge
time look E38AD214943DAAD1D64C102FAEC29DE4AFE9DA3D pwned-passwords-sha1-ordered-by-hash-v5.txt
E38AD214943DAAD1D64C102FAEC29DE4AFE9DA3D:2413945
0.01 real 0.00 user 0.00 sys`
not 49us, but fast enough for most use cases (purge should clear the fs cache)