The first argument of split is a regex, not a string. "|" is an alternative of two empty strings.

my @fields = split "|", 'abc|def';
print join ', ', @fields;  # a, b, c, |, d, e, f
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If you want to split on the literal vertical bar, you need to backslash it.

my @fields = split /\|/, 'abc|def';
print join ', ', @fields;  # abc, def
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