Your second solution is actually what I tried first but it is also slower than my current solution.

How exactly did you measure this - code, sample input, etc.? Because at least under the following conditions, my code suggestion appears to be faster than yours. (Note I inserted use warnings; use strict; at the top of my script.)

$ perl -wMstrict -le 'print join(" ",map {int(rand(100))-50} 0..rand(7
+)+3) for 1..1000000' >in.txt
$ wc -l in.txt 
1000000 in.txt
$ head -5 in.txt 
-49 43 0 -35 0 -20 -49 5 46 -11
-14 39 39 -24 -49 36 -7 -36 -43
15 30 5 -4 11
37 -25 27 -49 21
49 33 -15 -16 17 10 32 -14 -30
$ time perl 1190600.pl in.txt >out.txt

real    0m1.869s
user    0m1.863s
sys    0m0.004s
$ time perl 1190602.pl in.txt >out.txt

real    0m1.539s
user    0m1.521s
sys    0m0.016s

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In reply to Re^3: printing every 2nd entry in a list backwards by haukex
in thread printing every 2nd entry in a list backwards by Anonymous Monk

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