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If you have a question on how to do something in Perl, or you need a Perl solution to an actual real-life problem, or you're unsure why something you've tried just isn't working... then this section is the place to ask. Post a new question!

However, you might consider asking in the chatterbox first (if you're a registered user). The response time tends to be quicker, and if it turns out that the problem/solutions are too much for the cb to handle, the kind monks will be sure to direct you here.

User Questions
Wildcards for a wide array of strings?
7 direct replies — Read more / Contribute
by zarath
on May 23, 2017 at 04:01

    Perl-virgin here, be gentle, pretty please with sugar on top. + English is not my native tongue, but i pride myself in my capabilities (in written English anyways, I sound a bit like a mix of a Frenchman and a German trying to speak American).

    I have a question about the very first script I'm trying to write.

    I'm sure this will be resolved in a jiffy by the first person who bothers to read this whole thing. Will you be that person?

Backtracking in perl
3 direct replies — Read more / Contribute
by pdahal
on May 23, 2017 at 03:56
    hello monks! I was seeking for help about backtracking algorithm in perl. How can I backtrack the PubMed Abstract? Any helps are appreciated.
Hash Multiple values for a key-Filtering unique values for a key in hash
6 direct replies — Read more / Contribute
by rahulme81
on May 22, 2017 at 23:11

    Hi, Below is the output of hash. I get multipe values for my keys and values appeared more than one, I need to have only unique values for a key.

    $HASH1 = { 'Alabama' => ['Andalusia', 'Anniston', 'Clanton', 'Eufaula', 'Auburn', + 'Bessemer', 'Eufaula', 'Auburn', 'Bessemer' ], 'California' => ['Barstow','Barstow'], 'Georgia' => ['Darien'], 'New York' => ['Amsterdam','Coney Island','Coney Island','Beacon','Bec +on'] };

    for e.g. for key "California" I get values 'Barstow','Barstow' (same value two times), I need to retain the only one value 'Barstow'

    what is a good way to check the existence for a key that has multiple values? and keep the value unique so my output looks

    $HASH1 = { 'Alabama' => ['Andalusia', 'Anniston', 'Clanton', 'Eufaula', 'Auburn', + 'Bessemer'], 'California' => ['Barstow'], 'Georgia' => ['Darien'], 'New York' => ['Amsterdam','Coney Island','Becon'] };


CGI hangs unless print
4 direct replies — Read more / Contribute
by janedoh
on May 22, 2017 at 18:21
    Dear all,

    I have a CGI script which does a lot of things such as logging in to our large company database to get information.
    There is a foreach loop that goes through a list and foreach item contacts the db, gets info, etc etc. This hangs unless I
    put a print "." in the foreach loop. I'm unclear why this would happen. Could it be buffering? When I flush the output
    it doesn't help. It needs a print statement or it will hang.
    Any ideas?

    Thanks for your help.
Imager::File::TIFF Dependencies
3 direct replies — Read more / Contribute
by BrentD
on May 22, 2017 at 17:31
    I have written a program that allows me to input some info, then calls Imager to output the info as Group4 Fax encoded TIF files. I am running this under Windows 10 64-Bit. The program runs fine if I use the .pl file, but if I use pp to build an .exe file and copy to another system, the file will not run. This is my current pp command call:
    pp -M Imager::Font::W32 -M Imager::File::TIFF -M -a cbxarrow.xbm -a ar +rowdownwin.xbm -u -o Program.exe
    This is what happens when I run the .exe file:
    E:\>Program.exe Can't load 'C:\Users\generic\AppData\Local\Temp\par-67656e65726963\cac +he-1fbb3c46710e1a62d9823bf27f4a9fe7a961c4bb\c6dc6748.xs.dll' for modu +le Imager::File::TIFF: load_file:The specified module could not be fo +und at C:/Strawberry/perl/lib/ line 193. at C:/Strawberry/perl/lib/ line 95. DynaLoader::croak("Can't load 'C:\\Users\\generic\\AppData\\Lo +cal\\Temp\\par-67656e657"...) called at C:/Strawberry/perl/lib/DynaLo line 193 DynaLoader::bootstrap("Imager::File::TIFF", 0.89) called at C: +/Strawberry/perl/vendor/lib/PAR/ line 120 PAR::Heavy::_bootstrap("Imager::File::TIFF", 0.89) called at C +:/Strawberry/perl/lib/ line 102 DynaLoader::bootstrap_inherit("Imager::File::TIFF", 0.89) call +ed at Imager/File/ line 10 Imager::File::TIFF::BEGIN() called at Imager/File/ line + 11 eval {...} called at Imager/File/ line 11 require Imager/File/ called at TCTC/ line 6 require TCTC/ called at script/ line 32 main::BEGIN() called at Imager/File/ line 11 eval {...} called at Imager/File/ line 11 require main called at C:/Strawberry/perl/vendor/lib/ li +ne 636 PAR::_run_member(Archive::Zip::ZipFileMember=HASH(0x37e33b0), +1) called at script/ line 26 require main called at C:/Strawberry/perl/vendor/lib/ li +ne 636 PAR::_run_member(Archive::Zip::ZipFileMember=HASH(0x37e3698)) +called at C:/Strawberry/perl/vendor/lib/ line 428 PAR::import("PAR") called at -e line 631 eval {...} called at -e line 41 __par_pl::BEGIN() called at Imager/File/ line 11 eval {...} called at Imager/File/ line 11 BEGIN failed--compilation aborted at Imager/File/ line 11. Compilation failed in require at TCTC/ line 6. Compilation failed in require at script/ line 32. BEGIN failed--compilation aborted at script/ line 32. E:\>
    Seems obvious that I have some sort of missing dependency, but I can't seem to find what that might be. Any ideas?
Trouble with fork()
2 direct replies — Read more / Contribute
by phonybone_monk
on May 22, 2017 at 16:55

    Hello, perlmonks,

    I am seeking advice on diagnosing a problem related to a Perl program (which I inherited) that makes use of fork(). The basic problem seems to be that some of the forked sub-processes immediately exit without doing any work. When those processes are reaped (with wait()), $? is set to 11, which I believe is the error code for "resource temporarily unavailable, try again". I am trying to determine which resource is unavailable. The environment is Linux/Centos 7

    The basic structure of this program is as follows:

    • - Initialization
    • - Read in a large file (~10Gb)
    • - Do some processing of the input file using other open-source software (bowtie and samtools), via calls to system(). This results in the writing of some intermediate files.
    • - Process the intermediate files in parallel. For each processor core unit (as reported by Sys::Info::Device::CPU, or by reading /proc/cpuinfo), my program calls fork(). But instead of then calling exec(), the child continues processing on its own.
    • - The parent process, after spawning all the children, enters a loop around a call to wait(). If wait() returns -1, the parent prints a message that includes the value of $?, and then exits (via Carp::confess).

    Here's a pseudo code outline (note: this won't actually re-create my problem, of course):

    # Initialization # Read input file, calls to system('bowtie2', ...) and system('samtool +s', ...) use strict; use warnings; use Carp qw(confess); use Sys::Info::Device::CPU; use Sys::Info::Constants qw( :device_cpu ); my $info = Sys::Info->new; my $cpu = $info->device( CPU => {} ); my $nthreads = $cpu->count; print "$nthreads threads\n"; while ($nthreads--) { my $pid = fork; confess ("Can't fork: $!") unless defined $pid; if (! $pid) { print "child process: $$\n"; # this line never gets executed +by some of the children # Do a bunch of processing using intermediate files as input, usin +g Bio::DB::Sam->get_features_by_location() to access intermediate fil +es exit 0; } } # parent continues here: my $pid = 0; my $ok = 1; while ($pid != -1) { $pid = wait; last if $pid == -1; my $err=$?; if ($err) { print("one of the children died: pid=$pid, err=$err\n"); $ok = 0; } } if (! $ok) { confess "some child processes died."; } print "all done, yay\n";

    In all of the processes, the line directly after the fork confess("Can't fork: $!") unless defined $fork; never gets executed. I infer that the fork itself did happen.

    But some of the processes, depending on the input file, are reaped immediately, with $err=11 (EAGAIN). I surmise I am running short of some resource, but which one? I have increased the limits for the following resources to values (by editing /etc/security/limits.conf, and then rebooting) that I believe should be more than sufficient, to no avail:

    • - number of open file handles
    • - number of allowed processes per user
    • - number of file locks allowed
    • - amount of lockable memory
    I've also increased swap space via swap files.

    Short or restructuring the code to use exec(), which I've considered, do any wise monks have suggestions as to:

    • - how to determine which missing resource is causing fork() to exit with $?=EAGAIN?
    • - any other useful areas to examine?

    My thanks for all answers, insights, and useful comments

What is correct way to reference?
6 direct replies — Read more / Contribute
by BradV
on May 22, 2017 at 13:13

    I'm writing some code to parse some xml files. One element could either have a single value or an array of values. I have:

    if ( ref($xmlcollection->{phone}->{callTo}) eq "ARRAY" ) { printf( "Call To:" ); foreach ($xmlcollection->{phone}->{callTo}) { print "$_\n"; } } else { printf( "Call To: %s\n", $xmlcollection->{phone}->{callTo}); }

    It just prints the array reference. If I add:

    printf( "%s\n",$xmlcollection->{phone}->{callTo}[0]); printf( "%s\n", $xmlcollection->{phone}->{callTo}[1]);

    it prints the correct values. The problem is I don't always know how many elements will be in the array. How do I correctly reference the array element of the hash in order to print out all of the values?

\b in Unicode regex
3 direct replies — Read more / Contribute
by Arik123
on May 22, 2017 at 02:45

    Hi Monks!

    I do

    $string =~ /$_/

    and it matches. I do

    $string =~ /\b$_\b/

    and it doesn't match, for the same values of $string and $_. I think it should match, since there's a hyphen or a dot after $_ in $string, which I think should match \b. Both $string and $_ are Unicode. Could it be that \b doesn't function for Unicode strings?

why is the size of notebooks area smaller than main window
2 direct replies — Read more / Contribute
by madhusudhan_s
on May 22, 2017 at 00:49


    I am trying to write a program which has many notebooks and i found a reference code from the web as below which is exactly what i want. When i make the main window size 870x1000 i notice that the area where the notebooks are present is smaller than the main window. How should i modify this code such that the notebooks are as big as the main window?
    #!/usr/bin/perl use strict; use warnings; use Tk; use Tk::NoteBook; our $mw = MainWindow->new; $mw->geometry("870x1000"); my $canvas = $mw->Scrolled('Canvas',-bg=>'red')->pack; our $nb = $canvas->NoteBook; ### add 20 tabs to notebook for ( 1 .. 20 ){ my $title = "Untitled ($_)"; $nb->add( $_, -label => $title ); } ### embed the notebook widget into the canvas my $nb_in_canvas = $canvas->createWindow( 0,0,-window => $nb,-anchor = +> 'nw' ); $canvas->update; ### the whole notebook is larger than what can be initially displayed ### so we'll have to sroll it later on in the program $canvas->configure(-scrollregion => [0,0,$nb->reqwidth,$nb->reqheight] +); MainLoop;
scrape a webpage
2 direct replies — Read more / Contribute
by backyardbill
on May 21, 2017 at 23:26
    # ============ this is the HTML snipit from Firebug ================== +======== <td class="fex_standardblack_font_small" bgcolor="white"> <input id="chkEquipment" name="chkEquipment" value="72" type="checkbox +"> 4WD/AWD </td> # ====== this is the perl code snipit trying to access/extract the dat +a print "\n $node\n"; my $B = $tree->findvalue( $node ); $B = trim($B); print "\n $B \n"; # ============ this is what prints ================ /html/body/div/div[4]/div[2]/div[2]/form/div[3]/div/table[2]/tbody/t +r/td[3]/div/table/tbody/tr[1] 4WD/AWD # ============ this is my question ================ # # how do I access/extract the 'value="72"' data?

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