Here's my go with grep. If you put your keys into a hash you can use exists to see if it's one we want.

#!C:/Perl/bin/perl.exe

use strict;
use warnings;

my %keys = (
  a => undef,
  e => undef,
  i => undef,
  o => undef,
  u => undef,
);

my @records = qw{
  1|2|3|d|4
  1|2|3|a|4
  1|2|3|d|4
  1|2|3|o|4
};

my @final = grep {
  my @flds = split '\|', $_;
  my $third = $flds[3];
  exists $keys{$third}
} @records;

print "@final\n";
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You could make that shorter but this way gives you a better idea of what's happening. output:

1|2|3|a|4 1|2|3|o|4
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