Using Template Toolkit
perl -MTemplate -e 'Template->new()->process("12dayxmas.tt")'
12dayxmas.tt
[%
list = [
{ day => 'first', item => 'A partridge in a pear tree.'},
{ day => 'second', item => 'Two turtle doves, and '},
{ day => 'third', item => 'Three french hens, '},
{ day => 'fourth', item => 'Four calling birds, '},
{ day => 'fifth', item => 'Five gold rings, '},
{ day => 'sixth', item => 'Six geese a-laying, '},
{ day => 'seventh', item => 'Seven swans a-swimming, '},
{ day => 'eighth', item => 'Eight maids a-milking, '},
{ day => 'nineth', item => 'Nine ladies dancing, '},
{ day => 'tenth', item => 'Ten lords a-leaping, '},
{ day => 'eleventh', item => 'Eleven pipers piping, '},
{ day => 'twelfth', item => 'Twelve drummers drumming, '}
];
-%]
[%
FOREACH list;
present = item _ present;
-%]
On the [% day %] day of Christmas my true love gave me [% present %]
[% END %]