Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

How does Perl handle strings with embedded NULLs?

by strredwolf (Chaplain)
on Aug 12, 2000 at 20:40 UTC ( #27635=categorized question: print w/replies, xml ) Need Help??
Contributed by strredwolf on Aug 12, 2000 at 20:40 UTC
Q&A  > strings


I have a file (formmail's message-id cache file) that stores it's data as "<msgid>\000" for each entry.
If I slurp it all in, will Perl have a problem with it?

Answer: How does Perl handle strings with embedded NULLs?
contributed by Corion

There are places where embedded \000 characters will get you into trouble, but Perl can read and write such files without problems, since Perl uses counted strings.

Be warned though that passing such strings to anything like a system routine (like open() or -x), that take null-terminated strings as arguments, you will have problems or security holes.

Answer: How does Perl handle strings with embedded NULLs?
contributed by graff

If by "slurp it all in" you mean something like:

$/ = undef; $_ = <>;
then Perl will certainly have no trouble at all reading all the data and assigning it all to $_, no matter what it contains. It will print it all out to STDOUT or any file handle as well (but you may need to be careful if the file handle is actually a pipe to a less forgiving process).

Plain old line-based I/O will also treat nulls just like any other character that isn't (part of) a line terminatation -- lines containing nulls will be fully read and written.

Of course, sometimes it makes sense to use nulls as the input record separator:

# one way to replace nulls with newlines: $/ = "\x00"; while (<>) { s/\x00/\n/; print; }
In addition to matching nulls exactly with "\x00" in regexes, Perl also matches them via the "." wildcard, and the negated character classes "\S", "\D", "\W", and so on.

Please (register and) log in if you wish to add an answer

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • 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?

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

    How do I use this? | Other CB clients
    Other Users?
    Others chilling in the Monastery: (3)
    As of 2021-02-27 13:13 GMT
    Find Nodes?
      Voting Booth?

      No recent polls found