removing blank lines: "grep ." is really slow

[Ivan]

I used to use

grep .

for removing blank lines, until I realized how slow it is for large  
numbers of lines. So I switched to

grep -v '^$'

, which is as fast as one would expect (well, not with the grep that  
comes with MacOSX 10.5.8 (GNU grep version 2.5.1), but this seems to  
have been fixed sometime between 2.5.1 and 2.6.3).

Still, it seems like "grep ." should be a lot faster than it is. On my  
5-year-old powerbook, it takes about 1 second per thousand lines, when  
the number of lines is bigger than about ten thousand and most lines  
are nonblank. (For smaller numbers of lines, the runtime ramps up  
faster than linear in the number of lines, but it seems to level out  
to linear. Not a good linear, but linear nonetheless.)

best,
Ivan