THEY SLOWED DOWN UNPACK? *boggle* Aherm. At any rate, as always the answer is benchmark benchmark benchmark.

Using this script below to run tests over a ~40M test file, the substr version is fastest at ~4 seconds on a dual 1.42G G4 (the others take ~7.25s, ~9.2s, and ~12.7s respectively; all wall clock times, perl v5.8.1-RC3, ruby 1.8.2).

#!/bin/zsh

echo -n "Making test data . . ."
perl -le '$t = time - 5 * 86400 ; for( 1..1_000_000 ) { print scalar l
+ocaltime $t, " random " x (int(rand(3))+1); $t += int( rand( 120 ) + 
+120 ) }' > testlog
echo " done"

for i in 1 2 3 4 ; do time perl -lne 'print "<b>", substr($_,0,24), "<
+/b> ", substr($_,25)' testlog > /dev/null ; done

for i in 1 2 3 4 ; do time perl -lne '/^(.{24}) (.*)$/; print "<b>", $
+1, "</b> ", $2' testlog > /dev/null ; done

for i in 1 2 3 4 ; do time perl -lne '($d,$r)=unpack("A24A*", $_);prin
+t "<b>", $d, "</b>", $r' testlog > /dev/null ; done

for i in 1 2 3 4 ; do time ruby -lne 'print "<b>", $_[0,24], "</b> ", 
+$_[25,$_.length]' testlog > /dev/null ; done

rm testlog

exit 0
[download]