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• How can I asynchronously monitor a file in Perl?

  - by Hussain

  I am wondering if it is possible, and if so how, one could create a perl script that constantly monitors a file/db, and then call a subroutine to perform text processing if the file is changed. I'm pretty sure this would be possible using sockets, but this needs to be used for a webchat application on a site running on a shared host, and I'm not so sure sockets would be allowed on it. The basic idea is: create a listener for a chat file/database when the file is updated with a new message, call a subroutine the called subroutine will send the new message back to the browser to be displayed Thanks in advance.

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• How does this Perl grep work to determine the union of several hashes?

  - by titaniumdecoy

  I don't understand the last line of this function from Programming Perl 3e. Here's how you might write a function that does a kind of set intersection by returning a list of keys occurring in all the hashes passed to it: @common = inter( \%foo, \%bar, \%joe ); sub inter { my %seen; for my $href (@_) { while (my $k = each %$href) { $seen{$k}++; } } return grep { $seen{$_} == @_ } keys %seen; } I understand that %seen is a hash which maps each key to the number of times it was encountered in any of the hashes provided to the function.

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• What do you find wrong or strange in this Perl code to simulate objects without bless?

  - by user350571

  I'm new to Perl and its blessing stuff to imitate class like functionality made me feel strange I even had to go to the bathroom. Now, please tell me: what do you don't like, find wrong or strange with this code: sub Person { my $age = shift || 15; return { printAge => sub { print "Age -> $age\n"; }, changeAge => sub { $age = shift } } } my $p = Person(); my $p2 = Person(27); $p->{printAge}->(); $p->{changeAge}->(30); $p->{printAge}->(); $p2->{printAge}->();

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• How can I add a field with an array value to my Perl object?

  - by superstar

  What's the difference between these two constructors in perl? 1) sub new { my $class = shift; my $self = {}; $self->{firstName} = undef; $self->{lastName} = undef; $self->{PEERS} = []; bless ($self, $class); return $self; } 2) sub new { my $class = shift; my $self = { _firstName => shift, _lastName => shift, _ssn => shift, }; bless $self, $class; return $self; } I am using the second one so far, but I need to implement the PEERS array in the second one? How do I do it with the second constructor and how can we use get and set methods on those array variables?

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• Can I send a ESC d command to a POS printer from perl?

  - by Bradleyb

  I have a Star TSP100 printer and I'm having few problems with it really. My problem is that I'm not as familiar with programming as I should be - but I'm learning! The programmers reference for the Star printer says that if I send a ESC d to the printer - that will activate the built-in cutter - which I would like to do very much. My problem is that I have no idea how to send an escape code like that from within PERL - if it's even possible. I really appreciate any advice on this one.

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• Is there a Perl Syntax Highlighter (outputting to HTML) like PHP's GeSHi?

  - by nebukadnezzar

  Most PHP Developers are likely familar with the Syntax Highlighter called "GeSHi", which takes code, highlights it, with the use of HTML and CSS: include('geshi.php'); $source = 'echo "hello, world!"; $language = 'php'; $path = 'geshi/'; $geshi = new GeSHi($source, $language, $path); echo $geshi->parse_code(); GeSHi Supports a wide range of languages. I wonder, is there a similar Module for Perl?

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• How do you break on a specific line of a require'd file in the Perl debugger?

  - by Morinar

  I've got a Perl script, let's call it A.pl where the first two lines look something like this: require 'B.pl'; require 'C.pl'; Where both B.pl and C.pl each have their own cavalcade of requires. I need to set a breakpoint on a specific line of C.pl. In GDB I'd do something like: b C.pl:830 However that doesn't seem to work at all here. Is it possible? Am I close?

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• Why doesn't Perl threading work when I call readdir beforehand?

  - by Kevin

  Whenever I call readdir before I create a thread, I get an error that looks like this: perl(2820,0x7fff70c33ca0) malloc: * error for object 0x10082e600: pointer being freed was not allocated * set a breakpoint in malloc_error_break to debug Abort trap What's strange is that it happens when I call readdir before I create a thread (i.e. readdir is not called in any concurrent code). I don't even use the results from readdir, just making the call to it seems to screw things up. When I get rid of it, things seem to work fine. Some example code is below: opendir(DIR, $someDir); my @allFiles = readdir(DIR); close(DIR); my $thread = threads-create(\&sub1); $thread-join(); sub sub1 { print "in thread\n" }

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• How can I ignore C comments when I process a C source file with Perl?

  - by YoDar

  I'm running a code that read files, do some parsing, but need to ignore all comments. There are good explanations how to conduct it, like the answer to How can I strip multiline C comments from a file using Perl? $/ = undef; $_ = <>; s#/\*[^*]*\*+([^/*][^*]*\*+)*/|("(\\.|[^"\\])*"|'(\\.|[^'\\])*'|.[^/"'\\]*)#defined $2 ? $2 : ""#gse; print; My first problem is that after run this line $/ = undef; my code doesn't work properly. Actually, I don't know what it does. But if I could turn it back after ignoring all comments it will be helpful. In general, What is the useful way to ignore all comments without changing the rest of the code?

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• How can I plot a time series graph with Perl?

  - by Jazz

  I have some data from a database (SQLite), mapping a value (an integer) to a date. A date is a string with this format: YYYY-MM-DD hh:mm. The dates are not uniformly distributed. I want do draw a line graph with the dates on X and the values on Y. What is the easiest way to do this with Perl? I tried DBIx::Chart but I could not make it recognize my dates. I also tried GD::Graph, but as the documentation says: GD::Graph does not support numerical x axis the way it should. Data for X axes should be equally spaced

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• How can I read malformed XML (unencoded entities) with Perl?

  - by Mrouge

  I'm trying to parse an XML file I get from an external source but am having problems because there are unencoded XML entities in the text nodes. Essentially, I'm asking the same question as this, but for Perl instead of PHP. <report> <company>A & W</company> <company>Some Other Company with a < in Inc.</company> </report>

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• What do I gain by filtering URLs through Perl's URI module?

  - by sid_com

  Do I gain something when I transform my $url like this: $url = URI-new( $url )? #!/usr/bin/env perl use warnings; use strict; use 5.012; use URI; use XML::LibXML; my $url = 'http://stackoverflow.com/'; $url = URI->new( $url ); my $doc = XML::LibXML->load_html( location => $url, recover => 2 ); my @nodes = $doc->getElementsByTagName( 'a' ); say scalar @nodes;

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• How can I kill a Perl system call after a timeout?

  - by Fergal

  I've got a Perl script I'm using for running a file processing tool which is started using backticks. The problem is that occasionally the tool hangs and It needs to be killed in order for the rest of the files to be processed. Whats the best way best way to apply a timeout after which the parent script will kill the hung process? At the moment I'm using: foreach $file (@FILES) { $runResult = `mytool $file >> $file.log`; } But when mytool hangs after n seconds I'd like to be able to kill it and continue to the next file.

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• How can I run Perl system commands in the background?

  - by sid_com

  #!/usr/bin/env perl use warnings; use strict; use 5.012; use IPC::System::Simple qw(system); system( 'xterm', '-geometry', '80x25-5-5', '-bg', 'green', '&' ); say "Hello"; say "World"; I tried this to run the xterm-command in the background, but it doesn't work: No absolute path found for shell: & What would be the right way to make it work?

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• How can I get the path separator in Perl?

  - by ram

  In case of Java, we can get the path separator using System.getProperty("path.separator"); Is there a similar way in Perl? All I want to do is to find a dir, immediate sub directory. Say I am being given two arguments $a and $b; I am splitting the first one based on the path separator and joining it again except the last fragment and comparing with the second argument. The problem is my code has to be generic and for that I need to know whats the system dependent path separator is?

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• Why does Perl complain "Can't modify constant item in scalar assignment"?

  - by joe

  I have this Perl subroutine that is causing a problem: sub new { my $class = shift; my $ldap_obj = Net::LDAP->new( 'test.company.com' ) or die "$@"; my $self = { _ldap = $ldap_obj, _dn ='dc=users,dc=ldap,dc=company,dc=com', _dn_login = 'dc=login,dc=ldap,dc=company,dc=com', _description ='company', }; # Print all the values just for clarification. bless $self, $class; return $self; } what is wrong on this code : i got this error Can't modify constant item in scalar assignment at Core.pm line 12, near "$ldap_obj,"

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• Why do I get strange output from Perl using SQL?

  - by benjamin button

  Here is my Perl code: foreach my $line (@tmp_field_validation) { chomp $line; my ($cycle_code,$cycle_month,$cycle_year)= split /\s*\|\s*/, $line; $cycle_code=~ s/^\s*(.*)\s*$/$1/; $cycle_month=~ s/^\s*(.*)\s*$/$1/; $cycle_year=~ s/^\s*(.*)\s*$/$1/; print "$line\n"; print "$cycle_code|$cycle_month|$cycle_year"; } Here is the output: 1 10 2009 1 10 2009|| What's wrong over here? I expected the pipes to be between the variables. Why are the pipes getting printed after all the three variables?

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• Perl: How do I extract certain bits from a byte and then covert these bits to a hex value?

  - by Siegfried Hepp

  I need to extract certain bits of a byte and covert the extract bits back to a hex value. Example (the value of the byte is 0xD2) : 76543210 bit position 11010010 is 0xD2 Bit 0-3 defines the channel which is 0010b is 0x2 Bit 4-5 defines the controller which is 01b is 0x1 Bit 6-7 defines the port which is 11b is 0x3 I somehow need to get from the byte is 0xD2 to channel is 0x2, controller is 0x1, port is 0x3 I googled allot and found the functions pack/unpack, vec and sprintf. But I'm scratching by head how to use the functions to achieve this. Any idea how to achieve this in Perl ?

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• How can I convert SQL comments with -- to # using Perl?

  - by NJTechie

  I have various SQL files with '--' comments and we migrated to the latest version of MySQL and it hates these comments. I want to replace -- with #. I am looking for a recursive, inplace replace one-liner. This is what I have: perl -p -i -e 's/--/# /g'` ``fgrep -- -- * A sample .sql file: use myDB; --did you get an error I get the following error: Unrecognized switch: --did (-h will show valid options). p.s : fgrep skipping 2 dashes was just discussed here if you are interested. Any help is appreciated.

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• How can I use Perl to scrape a website that reveals its content with JavaScript?

  - by AmbroseChapel

  I need to write a Perl script to scrape a website. The website can only be scraped with JavaScript, and the user is on Windows. I got some way with Win32::IE::Mechanize on my work machine, which has IE6, but then I moved to my netbook which has IE8, and can't even get as far as fetching a simple page. Is Win32::IE::Mechanize up to date with the latest versions of IE? But, more to the point, given a recent WinXP machine, what's the quickest, easiest way to scrape a site which only reveals its content via JavaScript?

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• Is my Perl script grabbing environment variabless from "someplace else"?

  - by Michael Wilson

  On a Solaris box in a "mysterious production system" I'm running a Perl script that references an environment variable. No big deal. The contents of that variable from the shell both pre- and post-execution are what I expect. However, when reported by the script, it appears as though it's running in some other sub-shell which is clobbering my vars with different values for the duration of the script. Unfortunately I really can't paste the code. I'm trying to get an atomic case, but I'm at my wit's end here.

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• How can I convert floating point values in text to binary using Perl?

  - by YoDar

  I have text file looks like that: float a[10] = { 7.100000e+000 , 9.100000e+000 , 2.100000e+000 , 1.100000e+000 , 8.200000e+000 , 7.220000e+000 , 7.220000e+000 , 7.222000e+000 , 1.120000e+000 , 1.987600e+000 }; unsigned int col_ind[10] = { 1 , 4 , 3 , 4 , 5 , 2 , 3 , 4 , 1 , 5 }; Now, I want to convert each array (float / unsigned int) to different binary files - big endian type. Binary file for all float values and binary file for all integer values. What is the simple way to do it in Perl, consider I have over 2 millon elements in each array?

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• How can I send an html email with perl?

  - by alexBrand

  I am trying to send an HTML email using perl. open(MAIL,"|/usr/sbin/sendmail -t"); ## Mail Header print MAIL "To: $to\n"; print MAIL "From: $from\n"; print MAIL "Subject: $subject\n\n"; ## Mail Body print MAIL "Content-Type: text/html; charset=ISO-8859-1\n\n<html><head></head><body>@emailBody"; close(MAIL) Is that the correct way of doing it? It is not working for some reason. Thanks for your help.

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• Why does Perl allow mutual "use" relationships between modules?

  - by Haiyuan Zhang

  Let's say there are two modules that mutually use each other: package a; use b; sub p {} 1; package b; use a; 1; I think that it is systematically wrong to write code like the above, because the two modules will endlessly copy each other's code to themselves, but I can successfully run the following code, which makes me very surprised. Could any of you explain all of this to me? #! /usr/bin/perl use a; a->p();

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• In Perl, can I limit the length of a line as I read it in from a file (like fgets)

  - by SB

  I'm trying to write a piece of code that reads a file line by line and stores each line, up to a certain amount of input data. I want to guard against the end-user being evil and putting something like a gig of data on one line in addition to guarding against sucking in an abnormally large file. Doing $str = <FILE> will still read in a whole line, and that could be very long and blow up my memory. fgets lets me do this by letting me specify a number of bytes to read during each call and essentially letting me split one long line into my max length. Is there a similar way to do this in perl? I saw something about sv_gets but am not sure how to use it (though I only did a cursory Google search). Thanks.

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