perl5
The Perl 5 language interpreter (MIRROR ONLY)
Perl 5 - dev.perl.org
In the summary of differences between Perl 5 and Perl 6, it is noted that the wantarray function is gone:
wantarray() is gone
wantarray is gone. In Perl 6, context
flows outwards, which means that a
routine does not know which context it
is in.
Instead you should return objects that
do the right thing in every context.
Could someone provide an example of how such an object is created?
Source: (StackOverflow)
My scripts are getting too long. How do I split my code (procedural subs) into multiple Perl files and tell the interpreter to make sense of them?
Kind of like:
# -> main.pl
#include "foo.pl"
say_hello();
and:
# -> foo.pl
sub say_hello {print "hello!"}
Source: (StackOverflow)
Is there a readily available module for Perl that could scan an arbitrarily big nested structure of hashes and arrays and replace all identical branches (those that, for example, Test::Deep::cmp_deeply would say 'ok' about) with references to only a single value?
I have my own solution for this problem already, but I would prefer to use existing fast XS module if it is available.
Example of original structure as shown by Data::Dumper:
$VAR1 = {
'other_elems' => [
{
'sub_elements' => [
{'id' => 333},
{
'props' => ['attr5', 'attr6'],
'id' => 444
}
],
'other_key_for_attrs' => ['attr1', 'attr5'],
'id' => 222
},
{
'sub_elements' => [{'id' => 333}],
'id' => 111
}
],
'elems' => [
{
'attrs' => ['attr1', 'attr5'],
'id' => 1
},
{
'parent' => 3,
'attrs' => ['attr1', 'attr5'],
'id' => 2
},
{
'attrs' => ['attr5', 'attr6'],
'id' => 3
},
{
'attrs' => ['attr5', 'attr6'],
'id' => 4
}
]
};
Example of expected result structure:
$VAR1 = {
'other_elems' => [
{
'sub_elements' => [
{'id' => 333},
{
'props' => ['attr5', 'attr6'],
'id' => 444
}
],
'other_key_for_attrs' => ['attr1', 'attr5'],
'id' => 222
},
{
'sub_elements' =>
[$VAR1->{'other_elems'}[0]{'sub_elements'}[0]],
'id' => 111
}
],
'elems' => [
{
'attrs' => $VAR1->{'other_elems'}[0]{'other_key_for_attrs'},
'id' => 1
},
{
'parent' => 3,
'attrs' => $VAR1->{'other_elems'}[0]{'other_key_for_attrs'},
'id' => 2
},
{
'attrs' =>
$VAR1->{'other_elems'}[0]{'sub_elements'}[1]{'props'},
'id' => 3
},
{
'attrs' =>
$VAR1->{'other_elems'}[0]{'sub_elements'}[1]{'props'},
'id' => 4
}
]
};
Source: (StackOverflow)
For several hours now I am fighting a bug in my Perl program. I am not sure if I do something wrong or the interpreter does, but the code is non-deterministic while it should be deterministic, IMO. Also it exhibits the same behavior on ancient Debian Lenny (Perl 5.10.0) and a server just upgraded to Debian Wheezy (Perl 5.14.2). It boiled down to this piece of Perl code:
#!/usr/bin/perl
use warnings;
use strict;
use utf8;
binmode STDOUT, ":utf8";
binmode STDERR, ":utf8";
my $c = "";
open C, ">:utf8", \$c;
print C "š";
close C;
die "Does not happen\n" if utf8::is_utf8($c);
print utf8::decode($c) ? "Decoded\n" : "Undecoded\n";
It initializes Perl 5 interpreter in strict mode with warnings enabled, with character strings (as opposed to byte strings) and named standard streams encoded in UTF8 (internal notion of UTF-8, but pretty close; changing to full UTF-8 makes no difference). Then it opens a file handle to an “in-memory file” (scalar variable), prints a single two-byte UTF-8 character into it and examines the variable upon closure.
The scalar variable now always has UTF8 bit flipped off. However it sometimes contains a byte string (converted to character string via utf8::decode()) and sometimes a character string that just needs to flip on its UTF8 bit (Encode::_utf8_on()).
When I execute my code repeatedly (1000 times, via Bash), it prints Undecoded and Decoded with approximately the same frequencies. When I change the string I write into the “file”, e.g. add a newline at its end, Undecoded disappears. When utf8::decode succeeds and I try it for the same original string in a loop, it keeps succeeding in the same instance of interpreter; however, if it fails, it keeps failing.
What is the explanation for the observed behavior? How can I use file handle to a scalar variable together with character strings?
Bash playground:
for i in {1..1000}; do perl -we 'use strict; use utf8; binmode STDOUT, ":utf8"; binmode STDERR, ":utf8"; my $c = ""; open C, ">:utf8", \$c; print C "š"; close C; die "Does not happen\n" if utf8::is_utf8($c); print utf8::decode($c) ? "Decoded\n" : "Undecoded\n";'; done | grep Undecoded | wc -l
For reference and to be absolutely sure, I also made a version with pedantic error handling – same results.
#!/usr/bin/perl
use warnings;
use strict;
use utf8;
binmode STDOUT, ":utf8" or die "Cannot binmode STDOUT\n";
binmode STDERR, ":utf8" or die "Cannot binmode STDERR\n";
my $c = "";
open C, ">:utf8", \$c or die "Cannot open: $!\n";
print C "š" or die "Cannot print: $!\n";
close C or die "Cannot close: $!\n";
die "Does not happen\n" if utf8::is_utf8($c);
print utf8::decode($c) ? "Decoded\n" : "Undecoded\n";
Source: (StackOverflow)
Like C where gcc, borland and many more compilers are available, I am wondering whether any other Compiler/Interpreters are available for Perl 5?
From my reading, I understand there was perlcc which compiled the code into B:OP format and then interpreter was used to convert the optree to machine executable.
Source: (StackOverflow)
I have a file containing some fully capitalized words and some mixed-case words, and I want to extract the fully capitalized runs of words (contained in one line) – that is, things separated by \b and containing at least two capital letters and no lowercase letters. Everything is 7-bit.
So, for example, if a line is
The QUICK Brown fox JUMPs OV3R T4E LAZY DoG.
then I'd want to extract QUICK and OV3R T4E LAZY.
This is what I have so far:
while (<$fh>) { # file handle
my @array = $_ =~ /\b[^a-z]*[A-Z][^a-z]*[A-Z][^a-z]*\b/;
push @bigarray, @array;
}
Is there a more elegant way to do it than [^a-z]*[A-Z][^a-z]*[A-Z][^a-z]*?
Source: (StackOverflow)
I know that perl6 will definetely allow importing perl5 code but I'm not able to do this.
Here is perl6 code
use perl5:Net::FTP;
It reports an error
Is there any configuration issue or it is not ready yet?
Source: (StackOverflow)
I tried to install some modules to a new server (fedora core 18) but I'm betting this error:
Can't locate CPAN.pm in @INC (@INC contains: /usr/local/lib/perl5 /usr/local/share/perl5 /usr/lib/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5 /usr/share/perl5 .).
BEGIN failed--compilation aborted.
The module I need to install is : XML/Writer.pm
because I'm getting this error:
Can't locate XML/Writer.pm in @INC (@INC contains: /usr/local/lib/perl5 /usr/local/share/perl5 /usr/lib/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5 /usr/share/perl5 .
Any of you knows why or how can I fix this errors?
Source: (StackOverflow)
For debugging purposes I'd like to Access the lexical scope of different subroutines with a specific Attribute set. That works fine. I get a Problem when the first variable stores a string, then I get a empty string. I do something like this:
$pad = $cv->PADLIST; # $cv is the coderef to the sub
@scatchpad = $pad->ARRAY; # getting the scratchpad
@varnames = $scratchpad[0]->ARRAY; # getting the variablenames
@varcontents = $scratchpad[1]->ARRAY; # getting the Content from the vars
for (0 .. $#varnames) {
eval {
my $name = $varnames[$_]->PV;
my $content;
# following line matches numbers, works so far
$content = $varcontent[$_]->IVX if (scalar($varcontent[$_]) =~ /PVIV=/);
# should match strings, but does give me undef
$content = B::perlstring($varcontent[$_]->PV) if (scalar($varcontent[$_]) =~ /PV=/);
print "DEBUGGER> Local variable: ", $name, " = ", $content, "\n";
}; # there are Special vars that throw a error, but i don't care about them
}
Like I said in the comment the eval is to prevent the Errors from the B::Special objects in the scratchpad.
Output:
Local variable: $test = 42
Local variable: $text = 0
The first Output is okay, the second should Output "TEXT" instead of 0.
What am I doing wrong?
EDIT: With a little bit of coding I got all values of the variables , but not stored in the same indexes of @varnames and @varcontents. So now is the question how (in which order) the values are stored in @varcontents.
use strict;
use warnings;
use B;
sub testsub {
my $testvar1 = 42;
my $testvar2 = 21;
my $testvar3 = "testval3";
print "printtest1";
my $testvar4 = "testval4";
print "printtest2";
return "returnval";
}
no warnings "uninitialized";
my $coderef = \&testsub;
my $cv = B::svref_2object ( $coderef );
my $pad = $cv->PADLIST; # get scratchpad object
my @scratchpad = $pad->ARRAY;
my @varnames = $scratchpad[0]->ARRAY; # get varnames out of scratchpad
my @varcontents = $scratchpad[1]->ARRAY; # get content array out of scratchpad
my @vars; # array to store variable names adn "undef" for special objects (print-values, return-values, etc.)
for (0 .. $#varnames) {
eval { push @vars, $varnames[$_]->PV; };
if ($@) { push @vars, "undef"; }
}
my @cont; # array to store the content of the variables and special objects
for (0 .. $#varcontents) {
eval { push @cont, $varcontents[$_]->IV; };
eval { push @cont, $varcontents[$_]->PV; };
}
print $vars[$_], "\t\t\t", $cont[$_], "\n" for (0 .. $#cont);
EDIT2: Added runnable script to demonstrate the issue: Variablenames and variablevalues are not stored in the same index of the two Arrays (@varnames and @varcontents).
Source: (StackOverflow)
The question
What is the difference between Cwd::cwd and Cwd::getcwd in Perl, generally, without regard to any specific platform? Why does Perl have both? What is the intended use, which one should I use in which scenarios? (Example use cases will be appreciated.) Does it matter? (Assuming I don’t mix them.) Does choice of either one affect portability in any way? Which one is more commonly used in modules?
Even if I interpret the manual is saying that except for corner cases cwd is `pwd` and getcwd just calls getcwd from unistd.h, what is the actual difference? This works only on POSIX systems, anyway.
I can always read the implementation but that tells me nothing about the meaning of those functions. Implementation details may change, not so defined meaning. (Otherwise a breaking change occurs, which is serious business.)
What does the manual say
Quoting Perl’s Cwd module manpage:
Each of these functions are called without arguments and return the absolute path of the current working directory.
getcwd
my $cwd = getcwd();
Returns the current working directory.
Exposes the POSIX function getcwd(3) or re-implements it if it's not available.
cwd
my $cwd = cwd();
The cwd() is the most natural form for the current architecture. For most systems it is identical to `pwd` (but without the trailing line terminator).
And in the Notes section:
- Actually, on Mac OS, the
getcwd(), fastgetcwd() and fastcwd() functions are all aliases for the cwd() function, which, on Mac OS, calls `pwd`. Likewise, the abs_path() function is an alias for fast_abs_path()
OK, I know that on Mac OS1 there is no difference between getcwd() and cwd() as both actually boil down to `pwd`. But what on other platforms? (I’m especially interested in Debian Linux.)
1 Classic Mac OS, not OS X. $^O values are MacOS and darwin for Mac OS and OS X, respectively. Thanks, @tobyink and @ikegami.
And a little meta-question: How to avoid asking similar questions for other modules with very similar functions? Is there a universal way of discovering the difference, other than digging through the implementation? (Currently, I think that if the documentation is not clear about intended use and differences, I have to ask someone more experienced or read the implementation myself.)
Source: (StackOverflow)
Is it possible to pass a block of code to a sub using "parenthesis" syntax?
I.e. when i write
List::MoreUtils::any { defined ($_) } (undef, undef, 1);
it works. But when i try to add parenthesis
List::MoreUtils::any ( { defined ($_) } , (undef, undef, 1) );
this is interpreted as an anonymous hash, giving an error message. Neither escaping nor using eval helps.
The idea behind all the fuss is if the call is a part of an expression, i.e.
if (first_index { defined (${$_})} $jms_positions > $jms_positionals_seen )
some operator following the arguments might be executed before the call, producing an undesired result.
Source: (StackOverflow)
I need to create a several Perl programs on a Solaris 9 SPARC environment running Oracle EBS, one of which will be run from cron. The UNIX account that will be running Perl has all the environment variables set up to run Oracle-centric programs, so when I run "/usr/bin/perl -V", I get the following compilation error. Fortunately, the cron run Perl is not impacted by the Oracle environment settings.
bash-2.05$ /usr/bin/perl -V
Perl lib version (5.00503) doesn't match executable version (5.008) at /u01/app/applmgr/pr/iAS/Apache/perl/lib/5.00503/sun4-solaris/Config.pm line 7.
Compilation failed in require.
BEGIN failed--compilation aborted.
My first thought was to use the BEGIN block to do some house cleaning so I can use the system Perl rather than the Oracle EBS supplied version.
#!/usr/bin/perl
BEGIN {
delete $ENV{PERL5LIB};
delete @INC[0..$#INC];
push @INC, map { "/usr/local/lib/perl5/$_" } (
'5.8.0','5.8.0/sun4-solaris',
'site_perl','site_perl/5.8.0','site_perl/5.8.0/sun4-solaris'
);
}
print "Hello clean Perl environment! :)\n";
I am not permitted to modify the UNIX account's local profile, so is this the proper way to handle this scenario?
Source: (StackOverflow)
I have an array like ("valueA", "valueB", "valueC", "valueD") etc. I want to loop over the values of the array starting from (for example) the first instance of "valueC". Everything in the array before the first instance of the value "valueC" should be ignored; so in this case only "valueC" and "valueD" would be handled by the loop.
I can just put a conditional inside my loop, but is there a neater way to express the idea using perl?
Source: (StackOverflow)
In a Perl daemon reacting to various events I'm trying to use a Null object pattern in 2 cases by creating anonymous subroutines, which should just return a value of 1 aka "true" (please scroll to the right to see the check subroutines for LOGIN and ALIVE events):
package User;
our %EVENTS = (
LOGIN => {handler => \&handleLogin, check => sub {1}, },
CHAT => {handler => \&handleChat, check => \&mayChat, },
JOIN => {handler => \&handleJoin, check => \&mayJoin, },
LEAVE => {handler => \&handleLeave, check => \&mayLeave, },
ALIVE => {handler => sub {}, check => sub {1}, },
BID => {handler => \&handleBid, check => \&checkArgs, },
TAKE => {handler => \&handleTake, check => \&checkArgs, },
# .... more events ....
);
sub action($$$) {
my $user = shift;
my $event = shift;
my $arg = shift;
my $game = $user->{GAME};
unless (exists $EVENTS{$event}) {
print STDERR "wrong event: $event\n";
return;
}
my $handler = $EVENTS{$event}->{handler};
my $check = $EVENTS{$event}->{check};
return unless $user->$check->($arg); # XXX fails
$user->$handler->($arg);
}
sub mayChat($$) {
my $user = shift;
return if $user->{KIBITZER};
}
# ...... more methods here ...
1;
Unfortunately I get the runtime error for LOGIN event:
Can't use string ("1") as a subroutine ref while "strict refs" in use
Does anybody please know how to fix it here?
How to provide a "function pointer" to an anonymous Perl subroutine?
The handler => \&sub { 1 } doesn't do it either.
Using perl 5.8.8 and perl 5.10.1 on CentOS 5.x and 6.x
UPDATE:
I've also tried following:
my $check = $EVENTS{$event}->{check};
return unless $check->($user, $arg);
but it doesn't help. I think this rules out the "missing blessing" suggested in some answers.
UPDATE 2:
I have extended the source code snippet in my original question. The background is: I'm in the process of refactoring of my source code and thus I've created the %EVENTS hash as listed above, so that for each incoming event (a string sent over TCP-socket from a Flash client) there is a reference to a subroutine (check) which validates the event and a reference to another subroutine (handler) which performs some actions. I'm not sure if other subroutines work - I'm stuck already at the first LOGIN event.
I also don't understand why doesn't check => sub { 1 } above work - isn't sub supposed to return a reference to an anonymous subroutine (when the name is omitted - according to perldoc perlref section 4)?
UPDATE 3:
The output of print Dumper(\%EVENTS) -
$VAR1 = {
'PLAY' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'JOIN' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'OVER1' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'ALIVE' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'DISCARD' => {
'check' => $VAR1->{'PLAY'}{'check'},
'handler' => sub { "DUMMY" },
},
'MISS1' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'LOGIN' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'TAKE' => {
'check' => $VAR1->{'PLAY'}{'check'},
'handler' => sub { "DUMMY" },
},
'ONEMORE' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'OVER2' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'MISS2' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'EXACT' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'TRUST' => {
'check' => $VAR1->{'PLAY'}{'check'},
'handler' => sub { "DUMMY" },
},
'LEAVE' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'DEFEND' => {
'check' => $VAR1->{'PLAY'}{'check'},
'handler' => sub { "DUMMY" },
},
'OPEN' => {
'check' => $VAR1->{'PLAY'}{'check'},
'handler' => sub { "DUMMY" },
},
'REVEAL' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'CHAT' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'DECLARE' => {
'check' => $VAR1->{'PLAY'}{'check'},
'handler' => sub { "DUMMY" },
},
'BACK' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'MISERE' => {
'check' => sub { "DUMMY" },
'handler' => sub { "DUMMY" },
},
'BID' => {
'check' => $VAR1->{'PLAY'}{'check'},
'handler' => sub { "DUMMY" },
}
};
Source: (StackOverflow)