in reply to Unshift and push inside of map operation.

In my opinion (or "I personally believe" if you must) modifying an array with push/pop inside a map statement is one of those hints that there's a better way to go about a problem! :-)

The canonical form of map (according to me) is used to return a mapped version of the input: 

@a = map {
    # A function of $_, eg:
    $_ . ".txt"
} @a;

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One of the things I find particularly useful is that the block of code can evaluate to a list, including an empty one. Ie the output of map need not be the same length as the input. Eg 
# Emulate grep with map
@a = map { elementShouldBeIncluded($_) ? $_ : () } @a;

# Double up the list
@a = map { ($_, $_) } @a;

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In this particular case, this feature may be exactly what you're after, depending on how what exactly your vendor supplied program does. Consider the following structure: 

@a = map {
    # Is it a dir?
    (-d $_) ?
        # Expand it (somehow) into a list of files
        turnDirIntoFilesUsingVendorProg($_)
    :
        # It's a file - pass it straight through
        $_
} @a;

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Hope that helps.

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Re^2: Unshift and push inside of map operation.
by juster (Friar) on Sep 23, 2008 at 19:15 UTC

    The map solution was so cool and perlish that I had to try recursion with it!

    sub perlish {
    chomp;

    $_ = realpath($_); # follows links, makes full path

    ( -d )
    ? ( $processed{$_}
        ? ()
        : do {
            my $basedir = $_;
            $processed{$_} = 1; # prevent infinite recursion into link
+s

            # turn results of ls into relative paths before recursion
            # and avoids using chdir
            map &perlish, ( map {"$basedir/$_"} `ls $_` );
        }
      )
    : $_;
}

%processed = ( getcwd() => 1 );
print join "\n", (map &perlish, `ls`),"\n";

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    I love recursive maps now! It is MUCH prettier if you don't have to worry about symbolic links to dirs you already checked or relative paths:

    sub perlish {
    chomp;
    ( -d ) ? map &perlish, `find $_/* -maxdepth 0` : $_;
}
my @files = map &perlish, `find . -maxdepth 0`;

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