University:
Boston University
Course:
MET CS 201 | Introduction to Programming
Academic year:

2022
Views:

154

Pages:

20
Author:

impactwear3kz5

Swiss Army Chainsaw or Duct Tape of Internet? Perl gained its nickname of ‘Swiss army chainsaw’ for its flexibility and power; its ‘Duct Tape of Internet’ for its ability and often ‘ugly’, quick, easy fixes for solutions to various problems. Commonly referred applications: • • • • • Powerful text processing without data length limitation Regular expression and string parsing capability CGI (duct tape, glue language for Internet) DBI BioPerl Major versions • Perl 5 – almost rewrite of Perl interpreter, adding object-oriented (OO) feature, complex data structure, module and CGI support. Among them, module support plays critical role to CPAN’s establishment, and nowadays a great resource and strength for Perl community • Perl 6 – fundamentally different from Perl 5, dedicated to Larry’s birthday, goal is to fix all the warts in Perl 5; it’s said to be good at all that Perl 5 is good at, and a lot more. Language Scope • Perl is highly extensive language • Open source framework – CPAN model • CPAN and Perl Module • 191,032 available modules • 35, 637 distributions • written by 13,218 authors • mirrored on 250 servers Language Elements • Data Types – scalar, array, hash, reference • Control Structures – for, while, if, next, last, goto (yes, there is a Goto) • Regular Expressions • User Defined Extensions (Subroutines and functions) • Objects/modules/packages Advantage Over C • Perl runs on all platforms and is far more portable than C. • Perl and a huge collection of Perl Modules are free software (either GNU General Public License or Artistic License). • Perl is very efficient in TEXT and STRING manipulation i.e. REGEXP. • It is a language that combines the best features from many other languages and is very easy to learn. • Dynamic memory allocation is very easy in PERL, at any point of time we can increase or decrease the size of the array (i.e. splice(), push()) Disadvantage Over C • You cannot easily create a binary image ("exe") from a Perl file. It's not a serious problem on Unix, but it might be a problem on Windows. • Moreover, if you write a script which uses modules from CPAN, and want to run it on another computer, you need to install all the modules on that other computer, which can be a drag. • Perl is an interpretative language, so its comparatively slower to other compiling language like C. So, it’s not feasible to use in Real time environment like in flight simulation system. Some famous applications • Web CGI (EBay, Craigslist, BBC, Amazon, …) • 1000 Genome Project • Financial analysis (ease of use, speed for integration, rapid prototyping) - BarclaysCapital • Summarizing system logs/deal with Windows registry or Unix Passwd or groups file Get To Know Environment Connecting to SCC • Option 1: You are able to keep everything you generate Use your Shared Computing Cluster account if you have one. • Option 2: all that you do in the tutorial may be wiped out after tutorial ends unless you move the contents to somewhere belong to you. Tutorial accounts if you need one (will be offered in class). • Username: TBD • Password: TBD Exercise 1 - Where is My Perl Two commands to use: and ‘which perl’ ‘perl -v’ Do the experiment on next page to help understand the concept and discover more Exercise 1a - Where is My Perl Type ‘which perl’ in terminal Now type ‘perl -v’ Exercise 1b - Where is My Perl Type ‘module load perl’, then type ‘which perl’ in terminal Now type ‘perl -v’ Exercise 1 - Observation What’s the difference between Exercise 1a and 1b? What do we learn from Exercise 1 • Perl is an environment – means it can be changed by pointing to different installations. Exercise 2 – Perl Program Structure Open code examples in gedit and browse the content: codeEx_simplest.pl and codeEx_simplest.pl.nofirst Try to run the following commands: ./codeEx_simplest.pl ./codeEx_simplest.pl.nofirst What happened? Exercise 2 – Perl Program Structure (2) Here is what would be: Now try to run the following command: perl ./codeEx_simplest.pl.nofirst What happened? Exercise 2 – Perl Program Structure (3) Here is what would be this time: So why? Why is ‘perl’ in the command so critical to the 2nd code example? Topic: Perl program and OS Exercise 2 – Check Source Code Comments on Exercise 2 Comment#1: file name doesn’t matter (.pl is just a convention) Comment#2: file permission doesn’t matter (the file can be in plain readable text permission) Reason: in the first command, ./codeEx_simplest.pl, the file functions as an executable (in this case, the executable permission is a must), and inside the script, it must contains the location for the perl interpreter (which is what the first line of the code does) But in the second form with perl leading the command: the file functions as mere an input parameter to feed ‘perl’ command. The true executable from OS point is ‘perl’ program itself. What do we learn from Exercise 2 • Importance of the first line of almost every Perl script (Perl Interpreter is mandatory to be present) • This is why the path has to be specified in each Perl script to let the system know where to start (this is called ‘Entry Point’)