As tybalt89 already said, Slices (and perhaps the Range Operators if you haven't come across that yet).

my @header_line = ('id', 'name', 'age');
@fields{@header_line} = (0 .. $#header_line);

# is exactly equivalent to 

($fields{id},$fields{name},$fields{age}) = (0,1,2);
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