One possible solution:

use strict;
use warnings;

while (my $line = <DATA>) {
    my @pairs = split /[, ]+/, $line;
    my @values;
    push @values, (split /=/, $_)[1] for @pairs;
    print "@values";
}

__DATA__
field1=value1, field2=value2, field3=value3
field1=value1a, field2=value2a, field3=value3a
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This is the output obtained:

value1 value2 value3
value1a value2a value3a
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