I came up with something that seems to match your pipe/one liner closely. It doesn't chomp but you don't match against the end of line so I don't think that matters much.

use strict;
use warnings;

my $A="abc\ndef\nghi\n";

# remember matching is greedy but
# without /s modifier '.' does not match \n
my $B = join('', grep { ! /def/ } $A =~ /(.*\n)/g);
print $B;
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