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User Questions
using waitpid() with signals
No replies — Read more | Post response
by ristov
on Jan 20, 2017 at 14:59

    I am trying to write the code which would wait for the child process to exit -- but if the code gets the TERM signal while waiting, the child process should be terminated with the same signal. While waiting for the child can be easily done with waitpid(pid, 0), signals do not interrupt waitpid() with EINTR error code. To solve this problem, one could use the following code with non-blocking waitpit():

    $term = 0; $SIG{TERM} = sub { $term = 1; }; for (;;) { $p = waitpid($pid, WNOHANG); # where did the child disappear? if ($p == -1) { exit(1); } # child has terminated if ($p == $pid && (WIFEXITED($?) || WIFSIGNALED($?))) { exit($?>>8); } # TERM has arrived, forward it to child and exit if ($term) { kill('TERM', $pid); exit(0); } # check the child again after 1 second sleep(1); }

    However, I am interested whether the same task can be accomplished with blocking waitpid() which consumes less CPU time. There is one very interesting recipe which involves the use of eval:

    http://blog.kazuhooku.com/2015/02/writing-signal-aware-waitpid-in-perl.html

    Nevertheless, I am wondering whether it would be OK to use the blocking waitpid() with a different signal handler for the same purpose:

    # waitpid($pid,WNOHANG) returns 0 if the child process # exists and has not terminated $SIG{TERM} = sub { waitpid($pid,WNOHANG) || kill('TERM', $pid); exit(0 +); } # waitpid loop for (;;) { $p = waitpid($pid, 0); # where did the child disappear? if ($p == -1) { exit(1); } # child has terminated if ($p == $pid && (WIFEXITED($?) || WIFSIGNALED($?))) { exit($?>>8); } }

    In the signal handler, waitpid($pid, WNOHANG) is used for checking if the child process exists, in order to avoid sending TERM to a non-existing process. Since I am not too familiar with Perl internals, I am not sure if it is OK if the signal handler is invoked in the middle of blocking waitpid(), in order to call waitpid() again in non-blocking mode from the handler. Can anyone provide some insights? If this approach has flaws, I would go with previous code examples.

    regards, risto
Perl6::Form not printing 0 (zero)
2 direct replies — Read more / Contribute
by StuLong
on Jan 20, 2017 at 11:23

    I am using Perl6::Form, and have run into an issue wherein a numeric value of zero gets printed as octothorpes, as if the value is too large to fit the field. Happens for both single line and block format fields.

    Perl is v5.16.3 on RHEL7. Form is 0.06.

    use Perl6::Form; print form '{]].[}', [0,1];
    results in
    ###.## 1.0

    Field output is properly aligned on the decimal point, but the zero value field won't print. Anyone have any ideas how I can make my zeroes manifest themselves?

    Update. Things get weirder. After reading more in Perl6:Form docs, I tried one of the examples, and discovered that if I make the field in the example above slightly larger, the zeroes print, but are not properly formatted.

    print form '{]]].[}', [0,1]; 0.00. 1.0
Issues with Array of Hashes
2 direct replies — Read more / Contribute
by ciscomonkey
on Jan 20, 2017 at 10:54
    Having an issue with Text::CSV::Slurp not seeing my array of hashes. Here's some code that generates a hash just as my production script does:
    use Modern::Perl; use Text::CSV::Slurp; use Data::Dumper; sub generate { my %inline; $inline{'total'} = 2; $inline{'items'} = [ { 'name' => 'item1' }, { 'name' => 'item2' } ]; return \%inline; } my $ref = &generate(); print Dumper( $ref->{'items'} ); my $csv = Text::CSV::Slurp->create( input => $ref->{'items'} );
    I have multiple steps doing this same thing with no issue, and a quick Dumper output from those looks to be the exact same as the Dumper output from this code above. e.g. $VAR1 = [ {'key' => 'val' },{ 'key' => 'val' } ]; however it keeps coming back with "Need an an array of hashes input to create CSV from" and I'm a little lost as to why. I've even compared against those that work with the following:
    print "\$ref->{'items'} is " . ref( $ref->{'items'} ) . "\n"; foreach my $item ( @{ $ref->{'items'} } ) { print $item->{'name'} . " is " . ref( $item ) . "\n"; }
    Which yields:
    $ref->{'items'} is ARRAY item1 is HASH item2 is HASH
    And both look the same. I'm hoping I'm just missing something really simple here, but any help is appreciated.
Using an IO::File object stored in a Hash.
2 direct replies — Read more / Contribute
by jjs04
on Jan 20, 2017 at 10:47

    I have found something that I think should work, but does not work as expected. When I use Path::Class to open a file and save its handle to a variable, it works as expected.

    Sample 1:
    use Path::Class; my $filename = "data.txt"; my $handle = file($filename)->open('<:encoding(UTF-8)'); while (<$handle>) { chomp($_); print $_,"\n"; } close($handle);
    Sample 1 Output:
    1 2 3 4
    However, if I save the same in a hash, it does not. Sample 2:
    use Path::Class; my $filename = "data.txt"; my %hash = ( 'handle' => file($filename)->open('<:encoding(UTF-8)') ); while(<$hash{'handle'}>) { chomp($_); print $_,"\n"; } close($hash{'handle'});
    Sample 2 Output:
    IO::File=GLOB(0x6fdf28)
    What am I missing? I suspect it is something quite simple that I have not experienced before. Thank you for the assistance.

     

    Edit: As first indicated by BrowserUk, readline should be used. Because the diamond operator is used with readline and glob, there may be some ambiguity as to how the parser should proceed. When a hash element is used within the diamond operator (<$hash{$key}>), it is a glob, causing my difficulties.

    This following sample works as expected. Sample 4:
    use Path::Class; my $filename = "data.txt"; my %hash = ( 'handle' => file($filename)->open('<:encoding(UTF-8)') ); while(readline($hash{'handle'})) { chomp($_); print $_,"\n"; } close($hash{'handle'});
    Sample 4 Output:
    1 2 3 4
Constant code
4 direct replies — Read more / Contribute
by philiprbrenan
on Jan 20, 2017 at 10:26

    When I try:

    #!/usr/bin/perl sub aa{2} sub bb{2} my ($a, $b) = (aa, bb); my ($s, $t) = ((2*aa+bb), (2*$a+$b)); say STDERR "$a==", aa; say STDERR "$b==", bb; say STDERR "$s==$t";

    I get:

    2==2 2==2 4==6

    Please tell me what I am doing wrong, as I expected $s and $t to be equal

    It can't be perl It must be me Yet what it is I cannot see

    Thanks!

PERL searching through a file
2 direct replies — Read more / Contribute
by ssimone
on Jan 20, 2017 at 08:33
    Hi, i have this PERL problem that i need to solve. I need to write a PERL script, which receives the name of a file as a command line attributeARGV0. Then, through the keyboard, it should receive parameters, one by one(array of charachters) that need to be searched in the text from the file. The script should create new files (the number of new files should be the same as the number of parameters received from a keyboard) with the same name as the original file, but it needs to have "_parameter" where(instead of "parameter" it should be the actual name of the parameter). In those files, the script writes down the sentences where the searching parameter shows in the original file. Every sentence i seperated from another one with "." and/or a new line \n.
Requring minimum perl version in a cpanfile
2 direct replies — Read more / Contribute
by Anonymous Monk
on Jan 19, 2017 at 17:12
    I am using cpanfile with my app to try to make it easier to install for non-perl users.

    I added a line in cpanfile specifying the minimum perl version, but I was expecting it to bail if the requirement wasn't met.

    Instead, it only prints a line after it tries to install everything, saying the perl version isn't in the specified range.

    I also added the requires line inside an

    on 'configure' => sub { }
    , but it behaves the same.

    Is there a way to make it bail on the perl version, before it wastes time trying to install a bunch of modules?

Strawberry CPAN
4 direct replies — Read more / Contribute
by LloydRice
on Jan 19, 2017 at 17:11
    With Strawberry Perl, what is the preferred way to load CPAN modules? Should I go with the standard CPAN thing, or does Str. have a better way?
Browser Fingerprint
No replies — Read more | Post response
by freedurt
on Jan 19, 2017 at 16:06
    Hi PerlMonks

    I am looking for a solution to do some browser fingerprinting that goes beyond an IP check. I want to validate if someone coming into a CGI script is from a device I have seen in the past with some reasonable accuracy that is not an IP or Cookie check. I understand this is not fool-proof and users can and will switch browsers but nonetheless I would like to do a browser digital fingerprint and then exclude.

    So the question is... any code or module someone can provide that gives a reasonable browser digital fingerprint algorithm?

    It needs sit in the middle of being restrictive but not too restrictive (i.e. you could not just check useragent and say you are disallowed because the same useragent has already been seen).

    Based on my reading it would seem a combo between user agent and browser plugin details would work but I am not sure perl CGI can get plugin details?

    User Agent (1 in 4,184)
    HTTP_ACCEPT Headers (1 in 14)
    Browser Plugin Details (1 in 1.8 million)
    Time Zone (1 in 24)
    Screen Size and Color Depth (1 in 1,700)
    System Fonts (1 in 11)
    Cookies Enabled? (1 in 1.3)
    Limited SuperCookie test (1 in 2)

    http://softwareengineering.stackexchange.com/questions/122372/is-browser-fingerprinting-a-viable-technique-for-identifying-anonymous-users

    Thanks in advance for the help!

Unknown charnames when building Encode
2 direct replies — Read more / Contribute
by yulivee07
on Jan 19, 2017 at 03:23
    Hello fellow Perlmonks, I am trying to build Encode 2.88-3 from CPAN on AIX 7.2. During the make test phase I receive various errors about unknown characters:
    Use of uninitialized value $txt in pattern match (m//) at /usr/opt/per +l5/lib/5.20.1/_charnames.pm line 499. Unknown charname 'alpha' at t/Encode.t line 44, within string BEGIN not safe after errors--compilation aborted at t/Encode.t line 14 +8. t/Encode.t ................. t/encoding-locale.t ........ ok Use of uninitialized value $txt in pattern match (m//) at /usr/opt/per +l5/lib/5.20.1/_charnames.pm line 459. Unknown charname 'LATIN SMALL LETTER SHARP S' at t/encoding.t line 77, + within string BEGIN not safe after errors--compilation aborted at t/encoding.t line +165. Use of uninitialized value $txt in pattern match (m//) at /usr/opt/per +l5/lib/5.20.1/_charnames.pm line 459. Unknown charname 'POUND SIGN' at t/mime-header.t line 166, within stri +ng Execution of t/mime-header.t aborted due to compilation errors. # Looks like your test exited with 2 just after 1. t/mime-header.t ............
    To test whether this is an AIX problem or a perl problem, I tried to build the same version on my linux system, where Encode installs just fine.
    To pick the first error:
    is "\N{alpha}",substr($uni,0,1),"alpha does not map to symbol 'a'";
    It seems AIX perl is unable to find the \N{alpha} character. I am a bit lost here - where does perl usually search for characters like this?
    I need a hint into the direction I have to search for with this problem. Can someone provide some debugging tips?
    Updates:
    perl -E 'use charnames (); say $charnames::VERSION' 1.40 perl -C -E 'say "\x{3b1} - \x{df} - \x{a3}"' Wide character in say at -e line 1. &#945; - - perl -E 'use Unicode::UCD; say $Unicode::UCD::VERSION' 0.58 perl -MUnicode::UCD=charprops_all -E 'say charprops_all("U+$_")->{Age} + for qw{3b1 df a3}' "charprops_all" is not exported by the Unicode::UCD module Can't continue after import errors at -e line 0. perl -C -E 'say "\N{greek:alpha}"' Use of uninitialized value $txt in pattern match (m//) at /usr/opt/per +l5/lib/5.20.1/_charnames.pm line 459. Use of uninitialized value $txt in pattern match (m//) at /usr/opt/per +l5/lib/5.20.1/_charnames.pm line 499. Unknown charname 'greek:alpha' at -e line 1, within string Execution of -e aborted due to compilation errors.
    The build process is using CPAN (perl -MCPAN -eshell) to install modules. We use local::lib to install to a specific directory, rather than the system perl path. The perl we are using is the one coming with AIX 7.2, so we did not build perl ourself.
    perl -V Summary of my perl5 (revision 5 version 20 subversion 1) configuration +: Platform: osname=aix, osvers=6.1.0.0, archname=aix-thread-multi uname='aix blade08 1 6 00003c3ad100 ' config_args='-d -Dprefix=/usr/opt/perl5 -Dcc=xlc_r -Duseshrplib -D +usethreads' hint=recommended, useposix=true, d_sigaction=define useithreads=define, usemultiplicity=define use64bitint=undef, use64bitall=undef, uselongdouble=undef usemymalloc=n, bincompat5005=undef Compiler: cc='xlc_r -q32', ccflags ='-D_ALL_SOURCE -D_ANSI_C_SOURCE -D_POSIX +_SOURCE -qmaxmem=-1 -qnoansialias -qlanglvl=extc99 -DUSE_NATIVE_DLOPE +N -DNEED_PTHREAD_INIT -q32 -D_LARGE_FILES', optimize='-O', cppflags='-D_ALL_SOURCE -D_ANSI_C_SOURCE -D_POSIX_SOURCE -qmaxmem= +-1 -qnoansialias -qlanglvl=extc99 -DUSE_NATIVE_DLOPEN -DNEED_PTHREAD_ +INIT' ccversion='12.1.0.9', gccversion='', gccosandvers='' intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=4321 d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=8 ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', + lseeksize=8 alignbytes=8, prototype=define Linker and Libraries: ld='ld', ldflags =' -brtl -bdynamic -b32' libpth=/lib /usr/lib /usr/ccs/lib libs=-lbind -lnsl -ldbm -ldl -lld -lm -lcrypt -lpthreads -lc perllibs=-lbind -lnsl -ldl -lld -lm -lcrypt -lpthreads -lc libc=, so=a, useshrplib=true, libperl=libperl.a gnulibc_version='' Dynamic Linking: dlsrc=dl_aix.xs, dlext=so, d_dlsymun=undef, ccdlflags=' -bE:/usr/ +opt/perl5/lib/5.20.1/aix-thread-multi/CORE/perl.exp' cccdlflags=' ', lddlflags='-bhalt:4 -G -bI:$(PERL_INC)/perl.exp -b +E:$(BASEEXT).exp -bnoentry -lpthreads -lc -lm' Characteristics of this binary (from libperl): Compile-time options: HAS_TIMES MULTIPLICITY PERLIO_LAYERS PERL_DONT_CREATE_GVSV PERL_HASH_FUNC_ONE_AT_A_TIME_HARD PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP PERL_NEW_COPY_ON_WRITE PERL_PRESERVE_IVUV USE_ITHREADS USE_LARGE_FILES USE_LOCALE USE_LOCALE_COLLATE USE_LOCALE_CTYPE USE_LOCALE_NUMERIC USE_PERLIO USE_PERL_ATOF USE_REENTRANT_API Built under aix Compiled at Feb 6 2015 14:54:29 %ENV: PERL5LIB="/home/perl_ss/perl5/lib/perl5/aix-thread-multi:/home/per +l_ss/perl5/lib/perl5:/usr/local/lib/site_perl/5.8.8:/usr/local/site_p +erl/common" PERL5OPT="" PERL5_CPANPLUS_IS_RUNNING="9961732" PERL5_CPAN_IS_RUNNING="9961732" PERL_LOCAL_LIB_ROOT="/home/perl_ss/perl5" PERL_MB_OPT="--install_base /home/perl_ss/perl5" PERL_MM_OPT="INSTALL_BASE=/home/perl_ss/perl5" @INC: /home/perl_ss/perl5/lib/perl5/aix-thread-multi /home/perl_ss/perl5/lib/perl5/aix-thread-multi /home/perl_ss/perl5/lib/perl5 /usr/local/lib/site_perl/5.8.8/aix-thread-multi /usr/local/lib/site_perl/5.8.8 /usr/local/site_perl/common /usr/opt/perl5/lib/site_perl/5.20.1/aix-thread-multi /usr/opt/perl5/lib/site_perl/5.20.1 /usr/opt/perl5/lib/5.20.1/aix-thread-multi /usr/opt/perl5/lib/5.20.1 /usr/opt/perl5/lib/site_perl/5.8.8 /usr/opt/perl5/lib/site_perl

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