Gabor Szabo Perl trainer and developer

Gabor Szabo Perl trainer and developer http://szabgab.com Gabor Szabo about programming in Perl, automated testing, dynamic languages and everyting else en-us Copyright 2002-2012, Gabor Szabo szabgab@gmail.com 1901-01-01T00:00+00:00 1 hourly Perl Maven Cookbook http://szabgab.com/perl-maven-cookbook.html After a long period of yak shaving, yesterday I decided to go for the short-cut and set up a minimal system for the <a href="http://perlmaven.com/">Perl Maven</a> web site. For the full article visit <a href="http://szabgab.com/perl-maven-cookbook.html">Perl Maven Cookbook</a> Gabor Szabo 2012-05-03T10:04:27+00:00 Perl TODO for May 2012 http://szabgab.com/todo-2012-05.html In January I started to write <a href="http://szabgab.com/todo-2012.html">annual reports and TODOs</a>. In <a href="http://szabgab.com/todo-2012-02.html">February</a> and in <a href="http://szabgab.com/todo-2012-03.html">March</a> I published monthly updates. In March and April I was so busy with work at clients and holidays, that I could not even keep up with e-mail. Publishing the <a href="http://perlweekly.com/">Perl Weekly</a> was also hard. I could not even post my report at the beginning of April and there was not much point in any planning. I did not know how much time I'll be able to allocate. As the load now seem to lighten up, I try to collect what happened in the last 2 months and make some plans. For the full article visit <a href="http://szabgab.com/todo-2012-05.html">TODO for May 2012</a> Gabor Szabo 2012-05-01T10:22:09+00:00 Perl, TODO Facebook vs Google+ for Perl projects http://szabgab.com/facebook-vs-google-plus-for-perl-projects.html I guess the two dead-lines I have next week caused me to go in full procrastination mode and search for Perl based projects on Facebook and Google Plus. For the full article visit <a href="http://szabgab.com/facebook-vs-google-plus-for-perl-projects.html">Facebook vs Google+ for Perl projects</a> Gabor Szabo 2012-04-28T19:28:32+00:00 Perl, Facebook, Google Plus Splice to slice and dice arrays in Perl http://szabgab.com/splice-to-slice-and-dice-arrays-in-perl.html After learning about pop() and shift() students sometimes ask me how to remove an element from the middle of an array? I usually don't have time to explain it - there are other things to teach, that seem to be more important than splice() in the limited time we have, but I usually give them at least the direction. For the full article visit <a href="http://szabgab.com/splice-to-slice-and-dice-arrays-in-perl.html">Splice to slice and dice arrays in Perl</a> Gabor Szabo 2012-04-26T21:19:35+00:00 Perl, splice, array Perl Weekly two days later http://szabgab.com/perl-weekly-two-days-later.html Two days ago I wrote that the <a href="http://szabgab.com/perl-weekly-newsletter-at-3000.html">Perl Weekly reached 3000 subscribers</a>. The article was posted to <a href="http://news.ycombinator.com/item?id=3840406">Hacker News</a> and to <a href="http://www.reddit.com/r/perl/comments/s9b2o/the_perl_weekly_newsletter_reaches_3000/">Reddit</a>. I give some details on the numbers as I know you might be interested in this stuff. For the full article visit <a href="http://szabgab.com/perl-weekly-two-days-later.html">Perl Weekly two days later</a> Gabor Szabo 2012-04-15T20:19:30+00:00 Perl, Perl Weekly The Perl Weekly newsletter reaches 3000 subscribers http://szabgab.com/perl-weekly-newsletter-at-3000.html It is time for celebration. Yesterday the <a href="http://perlweekly.com/">Perl Weekly newsletter</a> reached 3000 subscribers! For the full article visit <a href="http://szabgab.com/perl-weekly-newsletter-at-3000.html">The Perl Weekly newsletter reaches 3000 subscribers</a> Gabor Szabo 2012-04-13T09:26:53+00:00 Perl Weekly, Perl Simple Database access using Perl DBI and SQL http://szabgab.com/simple-database-access-using-perl-dbi-and-sql.html While in most fields Perl adheres to the concept of TMTOWDI, in accessing relation databases Perl has a de-facto standard called DBI or Database independent interface for Perl. <h2>Architecture</h2> The Perl scripts use DBI which in turn uses the appropriate Database Driver (e.g. <a href="http://metacpan.org/release/DBD-Oracle">DBD::Oracle</a> for <a href="http://www.oracle.com/">Oracle</a>, <a href="http://metacpan.org/release/DBD-Pg">DBD::Pg</a> for <a href="http://www.postgresql.org/">PostgreSQL</a> and <a href="http://metacpan.org/release/DBD-SQLite">DBD::SQLite</a> to access <a href="http://sqlite.org/">SQLite</a>). Those drivers are compiled together with the C client libraries of the respective database engine. In case of SQLite, of course all the database engine gets embedded in the perl application. It is very hard to improve on the lovely ASCII-art that comes with the documentation of <a href="http://metacpan.org/release/DBI">DBI</a> so let me reproduce it here: <pre class="sh_perl"> |<- Scope of DBI ->| .-. .--------------. .-------------. .-------. | |---| XYZ Driver |---| XYZ Engine | | Perl | | | `--------------' `-------------' | script| |A| |D| .--------------. .-------------. | using |--|P|--|B|---|Oracle Driver |---|Oracle Engine| | DBI | |I| |I| `--------------' `-------------' | API | | |... |methods| | |... Other drivers `-------' | |... `-' </pre> <h2>Simple example</h2> I'll use SQLite to demonstrate the examples. That will make it very easy for you to try them on your computer. (e.g All versions of <a href="http://dwimperl.com/">DWIM Perl</a> already come with the necessary modules.) <pre class="sh_perl"> #!/usr/bin/perl use strict; use warnings; use DBI; my $dbfile = "sample.db"; my $dsn = "dbi:SQLite:dbname=$dbfile"; my $user = ""; my $password = ""; my $dbh = DBI->connect($dsn, $user, $password, { PrintError => 0, RaiseError => 1, AutoCommit => 1, FetchHashKeyName => 'NAME_lc', }); $dbh->disconnect; </pre> We load DBI but we do not explicitly load the database driver. That will be done by DBI. The DSN (Data Source Name) is very straight forward. It contains the type of the database. That will be the clue to DBI which DBD to load. In case of SQLite, the only thing we really need is the path to the database file. The username and password fields were left empty. I think they are not relevant at all for SQLite. The last parameter of the connect call is a reference to a hash containing some attributes I like to set. The DBI->connect call returns a database handle object that usually we store in a variable called $dbh. The call to disconnect from the database is optional as it will automatically be called when the variable $dbh goes out of scope but it having it might be a clear indication that you are done with the database. <h2>CREATE TABLE</h2> Of course having a connection is not enough. We need to be able to fetch data from the database or insert data into the database but for our example to work first we actually need to create the tables of the database. In this case we can do this with a single command: <pre class="sh_perl"> my $sql = <<'END_SQL'; CREATE TABLE people ( id INTEGER PRIMARY KEY, fname VARCHAR(100), lname VARCHAR(100), email VARCHAR(100) UNIQUE NOT NULL, password VARCHAR(20) ) END_SQL $dbh->do($sql); </pre> The first one is just a here document of an SQL statement to CREATE TABLE. Then we call the do method of the database handle which will send the SQL statement to the database. <h2>INSERT</h2> Now let's see the real thing, inserting data: <pre class="sh_perl"> my $fname = 'Foo'; my $lname = 'Bar', my $email = 'foo@bar.com'; $dbh->do('INSERT INTO people (fname, lname, email) VALUES (?, ?, ?)', undef, $fname, $lname, $email); </pre> To insert a row we call the $dbh->do method again but instead of passing the actual data, we put question-marks ? as place-holders. The SQL statement is followed by the word undef. That's actually the place of a hash-reference providing parameters to this specific call, similar to the attributes passed to the connect method but I think it is rarely used. That is followed by the actual values that go in place of the the place-holders. As you can see we did not have to put the place-holders in any kind of quotes nor did we have to somehow convert the values. DBI did it for us. This helps us avoid <a href="http://en.wikipedia.org/wiki/Sql_injection">SQL injection</a> attacks. Even if you meet someone called <a href="http://xkcd.com/327/">Bobby Tables</a>. <h2>UPDATE</h2> For updating some data in the database we also use the do method. <pre class="sh_perl"> my $password = 'hush hush'; my $id = 1; $dbh->do('UPDATE people SET password = ? WHERE id = ?', undef, $password, $id); </pre> Nothing special here. An SQL statement with some place-holders. undef instead of the extra attributes and the parameters to be used in place of the place-holders. <h2>SELECT</h2> This is by far the most interesting part of the database access. As the SELECT statement can return a lot of rows and a lot of values in each row we cannot use a simple call to the do method. Instead, there are several ways to fetch the data. I'll show here two. For both we have 3 steps: prepare the SQL statement. execute the statement with specific data and fetch the rows. From these, the prepare statement can be shared by - assuming the queries only differ in the data we pass to them. We create an SQL statement using question marks (?) as place-holders instead of actual values. This call returns a statement handle object that we usually save in a variable called $sth. Then we call the execute method of the statement handle passing to it values that should be placed instead of the place-holders. The third step is the really interesting one. In a while loop we fetch the results, row-by row. For this we can use several methods: The fetchrow_array method will return the values of the next row in the result set as a list, that we can assign to an array. The order of the elements is as the order of the fields in the query. (fname, lname in our case). The fetchrow_hashref method will return a reference to a hash. In the hash the keys will be the names of the fields in the database. As different databases might return these names of the fields in different cases we configured our database handler to make sure they - the names of the fields - will always converted to lower case. (That's what the FetchHashKeyName parameter did, when connecting to the database.) <pre class="sh_perl"> my $sql = 'SELECT fname, lname FROM people WHERE id > ? AND id < ?'; my $sth = $dbh->prepare($sql); $sth->execute(1, 10); while (my @row = $sth->fetchrow_array) { print "fname: $row[0] lname: $row[1]\n"; } $sth->execute(12, 17); while (my $row = $sth->fetchrow_hashref) { print "fname: $row->{fname} lname: $row->{lname}\n"; } </pre> <h2>Exercise</h2> Take the above snippets of code. Use the first one to set up the database and create a table. Then use the second one to insert a few people in the table. Finally use the last example to extract some data from the database and print it out. If you have any question, feel free to ask below. <h2>Thanks</h2> to sigzero for correcting a bug in the examples! <h2>Subscribe to my mailing list</h2> If you are interested getting updates when I post new articles, please subscribe to my newsletter: <div class="subscriberbox">   <form class="subscribe" action="http://szabgab.com/subscribe.html" method="POST" style="display:inline"> Enter your e-mail here: <input name="email" /> and click here: <input type="hidden" name="list" value ="update" /> <input type="submit" value="Sign Me Up!" /> </form> </div> Gabor Szabo 2012-04-05T22:12:40+00:00 Perl, SQL, DBI Perl Test Automation Training in Madison, Wisconsin and in Kiev, Ukraine http://szabgab.com/perl-test-automation-training-in-madison-wisconsin-and-kiev-ukraine.html I have two public Test Automation Training courses scheduled: The first one is planned to be on 10-11 May, the two days before <a href="http://event.perlrussia.org/yr2012/">Perl Mova and YAPC::Russia</a> in Kiev, Ukraine. If you are interested in this training, make sure you <a href="http://szabgab.com/contact.html">contact me</a> ASAP. The second one is <a href="http://yapcna.org/conference/testing-workshop">Testing Workshop</a> 11-12 June 2012 in Madison, Wisconsin, USA, just before <a href="http://yapcna.org/">YAPC::NA</a>. You can register on the web site. For the full article visit <a href="http://szabgab.com/perl-test-automation-training-in-madison-wisconsin-and-kiev-ukraine.html">Perl Test Automation Training in Madison, Wisconsin and in Kiev, Ukraine</a> Gabor Szabo 2012-04-02T09:16:58+00:00 Perl, testing, course Scalable Vector Graphics with Perl http://szabgab.com/scalable-vector-graphics-with-perl.html Scalable Vector Graphics allows you to create images that can scale up and down without loss of quality. I have already hear Tamir Lousky give two presentation on how to create SVG images using Perl, so I thought I should give it a try. For the full article visit <a href="http://szabgab.com/scalable-vector-graphics-with-perl.html">Scalable Vector Graphics with Perl</a> Gabor Szabo 2012-03-31T12:47:01+00:00 Perl, SVG How to create a Perl Module for code reuse? http://szabgab.com/how-to-create-a-perl-module-for-code-reuse.html In your system you are creating more and more scripts that need to use the same function. You know lots of Perl modules that allow you to use their functions and you also want it. You just don't know how to create such module. For the full article visit <a href="http://szabgab.com/how-to-create-a-perl-module-for-code-reuse.html">How to create a Perl Module for code reuse?</a> Gabor Szabo 2012-03-28T10:57:35+00:00 Perl