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Computer Interview Questions Answers

Perl Interview Questions Answers

Question - 11 : - What are scalar data and scalar variables?

Answer - 11 : - Perl has a flexible concept of data types. Scalar means a single thing, like a number or string. So the Java concept of int, float, double and string equals to Perl\'s scalar in concept and the numbers and strings are exchangeable. Scalar variable is a Perl variable that is used to store scalar data. It uses a dollar sign $ and followed by one or more alphanumeric characters or underscores. It is case sensitive.

Question - 12 : - How do I debug my Perl programs?

Answer - 12 : - Before you do anything else, you can help yourself by ensuring that you let Perl tell you about problem areas in your code. By turning on warnings and strictures, you can head off many problems before they get too big. You can find out more about these in strict and warnings. #!/usr/bin/perl use strict; use warnings; Beyond that, the simplest debugger is the print function. Use it to look at values as you run your program: print STDERR "The value is [$value]\n"; The Data::Dumper module can pretty-print Perl data structures: use Data::Dumper qw( Dumper ); print STDERR "The hash is " . Dumper( \%hash ) . "\n"; Perl comes with an interactive debugger, which you can start with the -d switch. you have Tk, you can use ptkdb. It's on CPAN and available for free. If you need something much more sophisticated and controllable, Leon Brocard's Devel::ebug (which you can call with the -D switch as -Debug) gives you the programmatic hooks into everything you need to write your own (without too much pain and suffering). You can also use a commercial debugger such as Affrus (Mac OS X), Komodo from Activestate (Windows and Mac OS X), or EPIC (most platforms).

Question - 13 : - Is there a Perl shell?

Answer - 13 : - The psh (Perl sh) is currently at version 1.8. The Perl Shell is a shell that combines the interactive nature of a Unix shell with the power of Perl. The goal is a full featured shell that behaves as expected for normal shell activity and uses Perl syntax and functionality for control-flow statements and other things. You can get psh at http://sourceforge.net/projects/psh/ . Zoidberg is a similar project and provides a shell written in perl, configured in perl and operated in perl. It is intended as a login shell and development environment. It can be found at http://pardus-larus.student.utwente.nl/~pardus/projects/zoidberg/ or your local CPAN mirror. The Shell.pm module (distributed with Perl) makes Perl try commands which aren't part of the Perl language as shell commands. perlsh from the source distribution is simplistic and uninteresting, but may still be what you want.

Question - 14 : - What is the easiest way to download the contents of a URL with Perl?

Answer - 14 : - Once you have the libwww-perl library, LWP.pm installed, the code is this: #!/usr/bin/perl use LWP::Simple; $url = get 'http://www.websitename.com/';

Question - 15 : - What is PERL?

Answer - 15 : - Perl is a high-level programming language with an eclectic heritage written by Larry Wall and a cast of thousands. It derives from the ubiquitous C programming language and to a lesser extent from sed, awk, the Unix shell, and at least a dozen other tools and languages. Perl's process, file, and text manipulation facilities make it particularly well-suited for tasks involving quick prototyping, system utilities, software tools, system management tasks, database access, graphical programming, networking, and world wide web programming. These strengths make it especially popular with system administrators and CGI script authors, but mathematicians, geneticists, journalists, and even managers also use Perl. Maybe you should, too.

Question - 16 : - Why do you use Perl?

Answer - 16 : - Perl is a powerful free interpreter. Perl is portable, flexible and easy to learn.

Question - 17 : - How to turn on Perl warnings? Why is that important?

Answer - 17 : - Perl is very forgiving of strange and sometimes wrong code, which can mean hours spent searching for bugs and weird results. Turning on warnings helps uncover common mistakes and strange places and save a lot of debugging time in the long run. There are various ways of turning on Perl warnings: For Perl one-liner, use -w option on the command line. On Unix or Windows, use the -w option in the shebang line (The first # line in the script). Note: Windows Perl interpreter may not require it. For other systems, choose compiler warnings, or check compiler documentation.

Question - 18 : - What does `new $cur->{LINK}' do? (Assume the current package has no new() function of its own.)    

Answer - 18 : - $cur->new()->{LINK} The indirect object syntax only has a single token lookahead. That means if new() is a method, it only grabs the very next token, not the entire following expression. This is why `new $obj[23] arg' does't work, as well as why `print $fh[23] "stuff\n"' does't work. Mixing notations between the OO and IO notations is perilous. If you always use arrow syntax for method calls, and nothing else, you'll not be surprised.

Question - 19 : - What does Perl do if you try to exploit the execve(2) race involving setuid scripts?

Answer - 19 : - Sends mail to root and exits. It has been said that all programs advance to the point of being able to automatically read mail. While not quite at that point (well, without having a module loaded), Perl does at least automatically send it.

Question - 20 : - How many ways can we express string in Perl?  

Answer - 20 : - Many. For example 'this is a string' can be expressed in: "this is a string" qq/this is a string like double-quoted string/ qq^this is a string like double-quoted string^ q/this is a string/ q&this is a string& q(this is a string)

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Rajeev Katiyar
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