c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my $s = 'first|second|third';
 my @ra = split '[|]', $s;
 dd \@ra;
"
["first", "second", "third"]
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Also works with  "[|]" and  /[|]/

Update: The reason  "\|" doesn't work is that in double-quote interpolation, the  \ (backslash) acts, in this case, on the  | (pipe) to produce a literal pipe. Double-quotish interpolation would need a doubled backslash to yield a single literal backslash in the compiled string:

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my $s = qq{\|};
 print qq{:$s:};
 ;;
 my $t = qq{\\|};
 print qq{:$t:};
"
:|:
:\|:
[download]

That's why it's generally better to use  qr{pattern} to compile a regex. (I use  qq{...} in the example because Windows command line uses "..." to quote everything and  qq{...} reduces the need for backslashes.) Contrast with  '\|' and  '\\|' Please see Quote and Quote-like Operators and Quote-Like Operators.