I think split behaves differently if the first parameter is a normal string instead of a regex. The perlfunc documentation doesn't mention this and I can't remember how exactly it differs. Anyway since | is a regex special character (alternation) you need to escape it. I'd normally write this as:

The reason you need two \s is because of the behaviour of double quotes - just try:

print "|";
print "\|";
print "\\|";
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and you should see what's happening.