This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

4.49: How do I process/modify each element of an array?

Use "for"/"foreach":

for (@lines) {
s/foo/bar/; # change that word
tr/XZ/ZX/; # swap those letters
}

Here's another; let's compute spherical volumes:

for (@volumes = @radii) { # @volumes has changed parts
$_ **= 3;
$_ *= (4/3) * 3.14159; # this will be constant folded
}

which can also be done with "map()" which is made to transform one list
into another:

Hi,

I have written quite a complex (at least for me) program of >10k lines of
code, packed in a main file and a dozen modules. While I am writing up the
publication (yep, it's a scientific program), I am wondering, what would be
the best way to package it.

Specifically, I would like to make the installation for the user as
painless as possible. Right now I write something along the lines "move
the Xxx directory into /usr/local/lib/site_perl or any other apropriate
directory with Perl modules", but this is hardly satisfactory.

I really have no experience with that, and regretfully, I will not have
time to devote a lot of attention to proper packaging, because other issues
around the publication are more pressing. Is there anything simple I could
do? I know I could use the PAR module (actually, I use pp to create
binaries), but I would much prefer to have a simple "clever" installer script.

Best regards,

January

I noticed that if I use a "CBC compatible" crypt module directly, I get
a normal expected result. But if I use CBC with the same cipher type on
the same key and plaintext I get a completely different result.

I've been up and down the perldoc for Crypt::CBC and just can't figure
out why the results differ so much. Because they differ so much you
can't use one method to decrypt the other.

For example:

use Crypt::CBC;
use Crypt::OpenSSL::AES;

$key = 'secretpassphrase';
$text = 'Crypt Test #0001';

my $en1 = new Crypt::OpenSSL::AES($key)->encrypt($text);

my $en2 = new Crypt::CBC(
-key => $key, -cipher => 'Crypt::OpenSSL::AES'
)->encrypt($text);

my $en1h = unpack('H*', $en1);
my $en2h = unpack('H*', $en2);

print "OpenSSL AES\n[$en1h]\n\n";
print "AES via CBC\n[$en2h]\n\n";

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

4.58: How can I know how many entries are in a hash?

If you mean how many keys, then all you have to do is use the keys()
function in a scalar context:

$num_keys = keys %%hash;

The keys() function also resets the iterator, which means that you may
see strange results if you use this between uses of other hash operators
such as each().

--------------------------------------------------------------------

dcruncher4@aim.com wrote:

Both are just languages. Neither one has any particular advantage in
maintenance, etc. It much more depends on the programmers who write the
code, how well the code is written and commented, the skills of the
people maintaining the code, and a bunch of other things.

This isn't about PerlSAX, but a package construct I found there in an
example using the module. I have no idea what's going on here so I'm
guessing. This appears in the code

my $handler = SaxHandler->new();

But there is no SaxHandler anywhere in the documentation ..... but
wait! Later in the code the author defines a package as in

package SaxHandler;

and in this package are subroutines with names of the callbacks, the
SAX event handling routines, that SAX will call for each different XML
event (starting ending new final ....)

I had no idea a package name could be used in such a fashion. I
appreciate some short discussion of what's going on. Thanks.

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

4.59: How do I sort a hash (optionally by value instead of key)?

(contributed by brian d foy)

To sort a hash, start with the keys. In this example, we give the list
of keys to the sort function which then compares them ASCIIbetically
(which might be affected by your locale settings). The output list has
the keys in ASCIIbetical order. Once we have the keys, we can go through
them to create a report which lists the keys in ASCIIbetical order.

my @keys = sort { $a cmp $b } keys %%hash;

foreach my $key ( @keys )
{
printf "%%-20s %%6d\n", $key, $hash{$key};
}

Hi guys,

i'm having a bit of a problem here with the exec functionality. I seem
to be unable to kill the children of my process. Hope you can help me
with this one.

I'm doing a client-server setup where the server requests the clients
to start instances of a certain application and now the bugger doesn't
seem to die properly. The code in nutshell is here, i'll eliminate my
crappy message handling and just quote the handler funcs:


$pid = fork;
if ( $pid == 0 )
{
exec( $my_command,$my_args) or die "can't do it Jim!";
} else {
$jobs{$pid} = $my_args;
}

hi, i have a perl program that calls another application. this second
application uses the value of certain environment variables during its
operation. i'm having trouble with unsetting those variables during
the course of the perl script.

my (wrong) pseudo code:

$var1 = $ENV{'VAR1};
$var2 = $ENV{'VAR2'};
$var3 = $ENV{'VAR3'};

system( "unsetenv VAR1");
system( "unsetenv VAR2");
system( "unsetenv VAR3");

run_the_external_app;

system( "setenv VAR1 $var1");
system( "setenv VAR2 $var2");
system( "setenv VAR3 $var3");

can someone tell me what the correct syntax should be for this?

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

4.51: How do I permute N elements of a list?

Use the "List::Permutor" module on CPAN. If the list is actually an
array, try the "Algorithm::Permute" module (also on CPAN). It's written
in XS code and is very efficient:

use Algorithm::Permute;

my @array = 'a'..'d';
my $p_iterator = Algorithm::Permute->new ( \@array );

while (my @perm = $p_iterator->next) {
print "next permutation: (@perm)\n";
}

For even faster execution, you could do:

use Algorithm::Permute;

my @array = 'a'..'d';