Time for the trusty old Benchmark.pm
But first check with B::Deparse 
print "Hey" if $responce eq "hi";
# is optimised/parsed to:
(($responce eq "hi") and print("Hey"));

[download]
So our favourite construct doesn't do what we think it will....

I couldn't get a definate answer out of Benchmark, but generally the fastest method is:
if ($responce eq "hi") { print "Hey" }
But the others aren't far behind 

print "Hey" if $responce eq "hi";
(($responce eq "hi") and print("Hey");

[download]
You would expect the second one of those to be faster if anything since that is what the first one is changed to, but maybe my tests were screwy.

Tests run on linux 5.005_03

Update: Okay I had another look at my Deparse results in relation to Adam's reply below. I generally use perl -MO=Deparse,-p -e ... since it adds extra bracketing and things so I can tell exactly how things are working in terms of precedence and stuff. It seems that using -p rearranges the foo if blah; to blah and foo but without -p, Deparse leaves it alone. So my question is, which result is more correct, does perl do the full transformation like Deparse,-p or does it just do the equivilent to plain Deparse before the next stage of complimation?

Here's where my benchmarks came from: 

my @foo = map {int rand 3} 1..1000;

timethese(-15, {
        one => 'for (@foo) { print "$_\n" if $_; }',
        two => 'for (@foo) { if ($_) {print "$_\n";} }',
        three => 'for (@foo) { ($_ and print("\n")); }',
        } );
__END__
Result:
  one: 15 wallclock secs (14.99 usr +  0.01 sys = 15.00 CPU) @ 9421.60
+/s (n=141324)
  two: 16 wallclock secs (15.01 usr + -0.01 sys = 15.00 CPU) @ 9217.53
+/s (n=138263)
three: 14 wallclock secs (15.43 usr +  0.01 sys = 15.44 CPU) @ 8842.75
+/s (n=136532)
another run
  one:  6 wallclock secs ( 7.00 usr +  0.01 sys =  7.01 CPU) @ 9369.33
+/s (n=65679)
three:  7 wallclock secs ( 7.57 usr +  0.00 sys =  7.57 CPU) @ 9237.78
+/s (n=69930)
  two:  7 wallclock secs ( 7.44 usr +  0.00 sys =  7.44 CPU) @ 8758.33
+/s (n=65162)
and another
  two:  9 wallclock secs ( 7.00 usr +  0.00 sys =  7.00 CPU) @ 9757.14
+/s (n=68300)
  one:  6 wallclock secs ( 7.00 usr +  0.01 sys =  7.01 CPU) @ 9133.24
+/s (n=64024)
three:  5 wallclock secs ( 7.06 usr +  0.00 sys =  7.06 CPU) @ 8828.47
+/s (n=62329)

[download]
Like I said it wasn't totally constant, so what did I do wrong in creating those benchmarks?

In reply to Re: Loops and speed by repson
in thread Loops and speed by damian1301

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