Beefy Boxes and Bandwidth Generously Provided by pair Networks
We don't bite newbies here... much
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
To elaborate a bit (it took me some experimenting to realize why cfreak is right), inside a map the variable $_ is magic. While each entry in the list is evaluated, $_ is an alias to that entry. Assigning a new value to $_ changes the value of the current list entry. Because you're calling screwed from within map without localizing $_, it's being assigned to each successive line in the file, and then set to undef to indicate end-of-file. When screwed returns, $_ is still set to undef, so all entries in the list are changed to undef.

You can verify this by changing screwed to:

sub screwed { $_ = 'hi'; }
in which case you'll get:
before a
before b
after hi
after hi

In reply to Re: Re: opening a file destroys nulling entries in a list?!?! by sgifford
in thread opening a file destroys nulling entries in a list?!?! by matpalm

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others making s'mores by the fire in the courtyard of the Monastery: (5)
    As of 2015-07-30 05:28 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (270 votes), past polls