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Diffstat (limited to 'tutorial.html')
| -rw-r--r-- | tutorial.html | 141 |
1 files changed, 121 insertions, 20 deletions
diff --git a/tutorial.html b/tutorial.html index 841472f..3db5d42 100644 --- a/tutorial.html +++ b/tutorial.html @@ -45,9 +45,9 @@ <p>Thanks to <tt>perl-MDK-Common</tt>'s own documentation, an easy way to directly access information about the provided - functions, you can use <tt>perldoc</tt>, for example - <tt>perldoc MDK::Common::Func</tt> will explain the functions - of the Func module. Use <tt>perldoc MDK::Common</tt> to view + functions is to use <tt>perldoc</tt>. For example, + <tt>perldoc MDK::Common::Func</tt> will list the functions + of the Func sub-module. Use <tt>perldoc MDK::Common</tt> to view information on all the available functions.</p> <p>Additionally, <tt>perl-MDK-Common</tt> provides a binary @@ -64,7 +64,7 @@ <p>Of course, a first look at the Perl language will be necessary for the reader. The following can be a good Perl - Tutorial (though there are many of them on the web): <a + Tutorial (although there are many others on the web): <a href="http://www.comp.leeds.ac.uk/Perl/">http://www.comp.leeds.ac.uk/Perl/</a>.</p> <p>Programming with <tt>perl-MDK-Common</tt> also emphasizes @@ -84,7 +84,7 @@ common technique among programmers, and maybe it's even worse with Perl programmers; but functional-style programs are often clearer, more expressive, more reusable, and more - maintainable</li> + maintainable, than traditional programs</li> <br> <li><b>strict code style:</b> Perl is known to be a language @@ -125,13 +125,13 @@ <p><b>Note:</b> many functions' name, extending capabilities of existing functions, or being their functional counterpart, are suffixed with the underscore character (<tt>_</tt>); for - example, <tt>chomp_</tt> is the equivalent of <tt>chomp</tt>, - but returns the chomp'ed results instead of modifying its - argument.</p> + example, <tt>chomp_</tt> is the semantical equivalent of + <tt>chomp</tt>, but returns the chomp'ed results instead of + modifying its argument.</p> <ul> <li> - <b>cat_</b>(FILENAME): returns the file contents: in scalar + <b>cat_</b>(FILENAME): returns the file contents; in scalar context it returns a single string, in array context it returns the lines. If the file doesn't exist, it returns <tt>undef</tt>. @@ -156,14 +156,12 @@ <b>output</b>(FILENAME, LIST): creates a file and outputs the list (if the file exists, it is clobbered) - <p>Counterpart of <tt>cat_</tt>. Build the contents of the file - in your program, and when you're happy with it, write it on - disk:</p> + <p>Counterpart of <tt>cat_</tt>:</p> <pre class="SCREEN"> - my @resolv_conf = qw(search mandrakesoft.com); - push @resolv_conf, "nameserver $_" foreach @name_servers; - output('/etc/resolv.conf', @resolv_conf); + output('/tmp/resolv.conf', + "search $domain\n", + map { "nameserver $_\n" } @name_servers); </pre> </li> @@ -276,7 +274,7 @@ # equivalent (but much more elegant!) to: - my @md_devices = map { /^(md\d+)/; $1 } grep { /^md\d+/ } cat_('/proc/mdstat'); + my @md_devices = map { /^(md\d+)/ } grep { /^md\d+/ } cat_('/proc/mdstat'); </pre> </li> @@ -294,8 +292,9 @@ <li> - <b>each_index</b> { CODE } LIST: just like <tt>each</tt>, but - sets $::i + <b>each_index</b> { CODE } LIST: iterate on a list to execute + some code needing the index of the list element (available in + <tt>$::i</tt>) <p>Useful when you need to perform an action on each element of a list, but you also need the index of each element:</p> @@ -313,13 +312,115 @@ <h2>perl_checker</h2> - <p></p> + <p>Let's examine now the code-style perl_checker wants you to + adopt. Let's consider the following naive code example:</p> + <pre class="SCREEN"> + 1: sub calc { + 2: my ($x,$y) = @_; + 3: $_ = $y; + 4: ($x==0 && $y==0) and return -1; + 5: my @tab = (1, 2, 3); + 6: + 7: /sysconfig\/i18n/ and return 1; + 8: } + </pre> + + <p> + The following problems are reported: + </p> + + <ul> + <li><pre class="SCREEN"> +line 2, character 12-12 +you should have a space here</pre> + + <p> + Good: <tt>my ($x, $y) = @_;</tt> + <br> + Why: you should put a space after the comma when specifying a list. + </p> + + <li><pre class="SCREEN"> +line 3, character 5-7 +undeclared variable $_</pre> + + <p> + Good: <tt>local $_ = $y;</tt> + <br> + Why: you should always localize <tt>$_</tt> when you set it, because it's a global variable. + </p> + + <li><pre class="SCREEN"> +line 4, character 8-8 +you should have a space here</pre> + + <p> + Good: <tt>($x == 0 && $y == 0) and return -1;</tt> + <br> + Why: you should put spaces before and after operators. + </p> + + <li><pre class="SCREEN"> +line 4, character 5-21 +unneeded parentheses</pre> + + <p> + Good: <tt>$x == 0 && $y == 0 and return -1;</tt> + <br> + Why: because of operators precedence, the parentheses are unneeded (if unsure about precedence, see <tt>perlop(1)</tt>) + </p> + + <li><pre class="SCREEN"> +line 5, character 8-12 +unused variable @tab</pre> + + <p> + Why: Assigning to unused variables is (typically) useless. If you really need to assign to an unused variable, prefix its name with `_' and perl_checker will stop boring you (for example, <tt>@_tab</tt>). + </p> + + <li><pre class="SCREEN"> +line 7, character 20-21 +change the delimit character / to get rid of this escape</pre> + + <p> + Good: <tt>m|sysconfig/i18n|</tt> + <br> + Why: <tt>/</tt> is not the only regexp delimiter! if you want to specify a slash in your regexp, use another delimiter so that your regexp will be more readable. + </p> + + </ul> + + <p>Finally, the correct code looks like:</p> + + <pre class="SCREEN"> + sub calc { + my ($x, $y) = @_; + local $_ = $y; + $x == 0 && $y == 0 and return -1; + my @_tab = (1, 2, 3); + + m|sysconfig/i18n| and return 1; + } + </pre> + + <p>Under Emacs, you might want to add the following to your + <tt>.emacs</tt> and then be able to validate your code with <tt>C-Enter</tt>:</p> + </p> + + <pre class="SCREEN"> + (defmacro ilam (&rest body) `(lambda () (interactive) ,@body)) + (add-hook 'cperl-mode-hook + '(lambda () + (local-set-key [(control return)] + (ilam (save-some-buffers 1) (compile (concat "perl_checker --restrict-to-files " (buffer-file-name (current-buffer)))))) + )) + </pre> <hr /> <p> - Last update: Fri Apr 18 22:08:06 2003 + Last update: Wed Apr 30 18:05:40 2003 </p> </body> |