Just to add something else, here is how map and grep would look if they didn't exist.

# @out = map { EXPRESSION } @in
my @out;
foreach $_ ( @in ) {
  push @out, EXPRESSION;
}

# @out = grep { CONDITION } @in
my @out;
foreach $_ ( @in ) {
  push @out, $_ if CONDITION;
}
[download]

Using the functions map and grep saves us typing these commonish constructs every time we need them.
Perl function list: <LAZY> map grep </LAZY> for foreach