What about if I want to make sure a module (Win32::DirSize) is installed? 
# see perldoc -f require for more info
my $class = 'Win32::DirSize';
eval "require $class" or die "Couldn't load $class: $@";

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And what about another program that only has one executable file? 
my $binary = "/path/to/executable";
-x $binary or die "$binary not found";

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In reply to Re^3: Detecting if a program or file exists by mattk
in thread Detecting if a program or file exists by FM

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