First-line-only editing, part 1: Typos trash timing

[Dan Bernstein]

Great, just great. I've now seen three messages all based on Bill's
results here. I said:

> | No, it's not. Try head -1 | sed 's/.../.../'; cat.

And he did:

> $ time { head -1; sed 's/foo/bar/'; cat; } < x.tmp > /dev/null

Can people read? Of course that's going to be slow: it shoves the whole
file through sed.

>   How 'bout that! The overhead of all the other stuff made it slower. I
> guess I'll vote for using just plain sed, because it's easier, faster,
> uses less memory, etc. I didn't create a multi-megabyte file, so there
> may be a break even point, but I wouldn't bet on it.

These incorrect conclusions are based on your tests of something
entirely different from what I said.

Now for some real timings:

Script started on Wed Oct 24 15:34:31 EDT 1990
csh> time
0.1u 0.3s 0:05 8% 0+232k 0+0io 0pf+0w
csh> sed '1s/foo/bar/g' < /etc/hosts > tsed
csh> time
1.4u 0.8s 0:30 7% 0+232k 7+39io 7pf+0w
csh> ( head -1 | sed 's/foo/bar/g' ; cat ) < /etc/hosts > tcat
csh> time
1.5u 1.2s 0:58 4% 0+232k 7+78io 7pf+0w
Script done on Wed Oct 24 15:36:07 EDT 1990

sed takes 1.3u and 0.5s. The cat-based solution takes 0.1u and 0.4s. And
/etc/hosts isn't very big. For really large files (several megabytes)
the margin approaches 12x.

Can we all agree here that sed is inefficient? (The above timings are
from a Sun 4, by the way.)

---Dan