What's the difference between grep and map in Perl?

Question

In Perl both grep and map take an expression and a list, and evaluate the expression for each element of the list.

What is the difference b

Answer 1

Think of grep as map with a filter. map iterates and provides an opportunity to do something with every item. For example these two lines are equivalent:

my @copy = @original;
my @copy = map {$_} @original;

Similarly, these two are equivalent:

my @copy = grep {-f $_} @original;

@copy = ();
for (@original)
{
  push @copy, $_ if -f $_;
}

grep provides the ability to insert a conditional, and therefore becomes a filter.