Keeping the default in the %par hash could be one way. Seems relatively clean to me...
#!/usr/bin/perl
use strict; # https://perlmonks.org/?node_id=11145036
use warnings;
my %par = map { split ' ', $_, 2 } split /\n/, <<END;
margin-left defaults to margin-horizontal
margin-horizontal defaults to margin
margin 20
margin-right 3
margin-bottom defaults to margin-right
END
use Data::Dump 'dd'; dd 'dump of %par', \%par;
sub get
{
my $want = shift;
$want = $1 while ($par{$want} // '') =~ /^defaults to (.+)/;
return $par{$want} // 'not defined';
}
for my $parameter ( sort 'margin-top', keys %par )
{
printf "%30s => %s\n", $parameter, get($parameter);
}
Outputs:
(
"dump of %par",
{
"margin" => 20,
"margin-bottom" => "defaults to margin-right",
"margin-horizontal" => "defaults to margin",
"margin-left" => "defaults to margin-horizontal",
"margin-right" => 3,
},
)
margin => 20
margin-bottom => 3
margin-horizontal => 20
margin-left => 20
margin-right => 3
margin-top => not defined
UPDATE: fixed typo in regex