s/// operates on $_. It returns the number of substitutions. In map, each list argument is aliased to $_.

my @newlist = map {
                    my $l = $_;
                    $l =~ s/\/etc\///;
                    my $l2 = $l;
                  }  @oldlist;
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You just need to return at the end, not assign (and you can save some backwhacking in your s/// by picking a different delimiter):

my @newlist = map {
                    my $l = $_;
                    $l =~ s|/etc/||;
                    $l;
                  }  @oldlist;
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Or you can use Filter() from Algorithm::Loops.

Update: I forgot about the 'r' modifier for s///. It makes s/// return the new value. So if you have a new enough perl, you can do:

my @newlist = s|/etc||r, @oldlist;
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