map BLOCK LIST
       map EXPR,LIST
               Evaluates the BLOCK or EXPR for each element of
               LIST (locally setting "$_" to each element) and
               returns the list value composed of the results of
               each such evaluation.  In scalar context, returns
               the total number of elements so generated.  Evalu­
               ates BLOCK or EXPR in list context, so each ele­
               ment of LIST may produce zero, one, or more ele­
               ments in the returned value.

                   @chars = map(chr, @nums);

               translates a list of numbers to the corresponding
               characters.  And

                   %hash = map { getkey($_) => $_ } @array;

               is just a funny way to write

                   %hash = ();
                   foreach $_ (@array) {
                       $hash{getkey($_)} = $_;
                   }
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So, for each element in @edittypes (let's say $_ = 'foo'), it would spit out \.foo. The return value from map would be a list of these transformed elements.

Update: Corrected escaping of backslash.

 
$regex = join('|', map{"\\.$_" }@edittypes);
 inerror("You can only edit \"@edittypes\"") unless /$regex/i;
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Im confused with whole thing can oyu explain in words how it does it.

OK, Let's say @edittypes = ( 'foo', 'bar', 'zoot' ). For each of these, map sets $_ to the array element, and spits out the return value of the block. So, map returns ( '\.foo', '\.bar', '\.zoot' ). These are joined with pipes; after executing the first line, you have $regex = '\.foo|\.bar|\.zoot'.

Now, since you don't appear to be matching to anything in the second line, I am guessing this came from inside a loop with an implicit value. Whatever $_ is equal to when the second line runs is matched against $regex, case insensitive. If there's no match, call the inerror function, whatever that may be.

Does that clear it up?

Update: Corrected escaping of backslash.


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What is the map function

See Map: The Basics.

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