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From: bush@ecs.ox.ac.uk (Mark Bush)
Newsgroups: comp.lang.perl
Subject: Re: First impressions of new perl user (code, questions, ...)
Message-ID: <1495@culhua.prg.ox.ac.uk>
Date: 25 Mar 91 17:01:55 GMT
References: <MAYER.91Mar21141900@porky.sono.uucp> <126310@uunet.UU.NET>
Sender: news@prg.ox.ac.uk
Organization: Oxford University Computing Laboratory
Lines: 45

In article <126310@uunet.UU.NET> rbj@uunet.UU.NET (Root Boy Jim) writes:
>In article <MAYER.91Mar21141900@porky.sono.uucp> mayer@sono.uucp (Ronald &) writes:
>?A random idea (not really a request; just something I was thinking about):
>?
>?In the unpack function do "A" and "a" mean the same thing?
>
>Obviously not.
>
>?If not, are the differences documented (not in my man page).

But the man page *does* document the difference (and a very useful
difference it is, too!

>To be honest, I couldn't quote you the exact differences,
>chapter and verse.

From the man page:

"    pack(TEMPLATE,LIST)
             Takes an array or list of values and packs it into a
             binary  structure,  returning  the string containing
             the structure.  The TEMPLATE is a sequence of  char-
             acters  that  give  the order and type of values, as
             follows:

                  A    An ascii string, will be space padded.
                  a    An ascii string, will be null padded."


so:

$a = pack("a4", "ab");
$b = pack("A4", "ab");
print "a is <$a>, b is <$b>\n";
printf "length(a) = %d, length(b) = %d\n", length($a), length($b);

will produce:

a is <ab>, b is <ab  >
length(a) = 4, length(b) = 4

print pack("A5", "Just"), pack("A8", "another"), pack("A5", "Perl"),
pack("A7", "hacker,");

Mark