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PERLSTYLE(1)	       Perl Programmers Reference Guide 	  PERLSTYLE(1)

       perlstyle - Perl style guide

       Each programmer will, of course, have his or her own preferences in
       regards to formatting, but there are some general guidelines that will
       make your programs easier to read, understand, and maintain.

       The most important thing is to run your programs under the -w flag at
       all times.  You may turn it off explicitly for particular portions of
       code via the "no warnings" pragma or the $^W variable if you must.  You
       should also always run under "use strict" or know the reason why not.
       The "use sigtrap" and even "use diagnostics" pragmas may also prove

       Regarding aesthetics of code lay out, about the only thing Larry cares
       strongly about is that the closing curly bracket of a multi-line BLOCK
       should line up with the keyword that started the construct.  Beyond
       that, he has other preferences that arent so strong:

	  4-column indent.

	  Opening curly on same line as keyword, if possible, otherwise line

	  Space before the opening curly of a multi-line BLOCK.

	  One-line BLOCK may be put on one line, including curlies.

	  No space before the semicolon.

	  Semicolon omitted in "short" one-line BLOCK.

	  Space around most operators.

	  Space around a "complex" subscript (inside brackets).

	  Blank lines between chunks that do different things.

	  Uncuddled elses.

	  No space between function name and its opening parenthesis.

	  Space after each comma.

	  Long lines broken after an operator (except "and" and "or").

	  Space after last parenthesis matching on current line.

	  Line up corresponding items vertically.

	  Omit redundant punctuation as long as clarity doesnt suffer.

       Larry has his reasons for each of these things, but he doesnt claim
       that everyone elses mind works the same as his does.

       Here are some other more substantive style issues to think about:

	  Just because you CAN do something a particular way doesnt mean
	   that you SHOULD do it that way.  Perl is designed to give you sev
	   eral ways to do anything, so consider picking the most readable
	   one.  For instance

	       open(FOO,$foo) || die "Cant open $foo: $!";

	   is better than

	       die "Cant open $foo: $!" unless open(FOO,$foo);

	   because the second way hides the main point of the statement in a
	   modifier.  On the other hand

	       print "Starting analysis\n" if $verbose;

	   is better than

	       $verbose && print "Starting analysis\n";

	   because the main point isnt whether the user typed -v or not.

	   Similarly, just because an operator lets you assume default argu
	   ments doesnt mean that you have to make use of the defaults.  The
	   defaults are there for lazy systems programmers writing one-shot
	   programs.  If you want your program to be readable, consider sup
	   plying the argument.

	   Along the same lines, just because you CAN omit parentheses in many
	   places doesnt mean that you ought to:

	       return print reverse sort num values %array;
	       return print(reverse(sort num (values(%array))));

	   When in doubt, parenthesize.  At the very least it will let some
	   poor schmuck bounce on the % key in vi.

	   Even if you arent in doubt, consider the mental welfare of the
	   person who has to maintain the code after you, and who will proba
	   bly put parentheses in the wrong place.

	  Dont go through silly contortions to exit a loop at the top or the
	   bottom, when Perl provides the "last" operator so you can exit in
	   the middle.	Just "outdent" it a little to make it more visible:

		   for (;;) {
		     last LINE if $foo;
		       next LINE if /^#/;

	  Dont be afraid to use loop labels--theyre there to enhance read
	   ability as well as to allow multilevel loop breaks.	See the previ
	   ous example.

	  Avoid using "grep()" (or "map()") or backticks in a void context,
	   that is, when you just throw away their return values.  Those func
	   tions all have return values, so use them.  Otherwise use a "fore
	   ach()" loop or the "system()" function instead.

	  For portability, when using features that may not be implemented on
	   every machine, test the construct in an eval to see if it fails.
	   If you know what version or patchlevel a particular feature was
	   implemented, you can test $] ($PERL_VERSION in "English") to see if
	   it will be there.  The "Config" module will also let you interro
	   gate values determined by the Configure program when Perl was

	  Choose mnemonic identifiers.	If you cant remember what mnemonic
	   means, youve got a problem.

	  While short identifiers like $gotit are probably ok, use under
	   scores to separate words in longer identifiers.  It is generally
	   easier to read $var_names_like_this than $VarNamesLikeThis, espe
	   cially for non-native speakers of English. Its also a simple rule
	   that works consistently with "VAR_NAMES_LIKE_THIS".

	   Package names are sometimes an exception to this rule.  Perl infor
	   mally reserves lowercase module names for "pragma" modules like
	   "integer" and "strict".  Other modules should begin with a capital
	   letter and use mixed case, but probably without underscores due to
	   limitations in primitive file systems representations of module
	   names as files that must fit into a few sparse bytes.

	  You may find it helpful to use letter case to indicate the scope or
	   nature of a variable. For example:

	       $ALL_CAPS_HERE	constants only (beware clashes with perl vars!)
	       $Some_Caps_Here	package-wide global/static
	       $no_caps_here	function scope my() or local() variables

	   Function and method names seem to work best as all lowercase.
	   E.g., "$obj->as_string()".

	   You can use a leading underscore to indicate that a variable or
	   function should not be used outside the package that defined it.

	  If you have a really hairy regular expression, use the "/x" modi
	   fier and put in some whitespace to make it look a little less like
	   line noise.	Dont use slash as a delimiter when your regexp has
	   slashes or backslashes.

	  Use the new "and" and "or" operators to avoid having to parenthe
	   size list operators so much, and to reduce the incidence of punctu
	   ation operators like "&&" and "||".	Call your subroutines as if
	   they were functions or list operators to avoid excessive ampersands
	   and parentheses.

	  Use here documents instead of repeated "print()" statements.

	  Line up corresponding things vertically, especially if itd be too
	   long to fit on one line anyway.

	       $IDX = $ST_MTIME;
	       $IDX = $ST_ATIME       if $opt_u;
	       $IDX = $ST_CTIME       if $opt_c;
	       $IDX = $ST_SIZE	      if $opt_s;

	       mkdir $tmpdir, 0700 or die "cant mkdir $tmpdir: $!";
	       chdir($tmpdir)	   or die "cant chdir $tmpdir: $!";
	       mkdir tmp,   0777 or die "cant mkdir $tmpdir/tmp: $!";

	  Always check the return codes of system calls.  Good error messages
	   should go to "STDERR", include which program caused the problem,
	   what the failed system call and arguments were, and (VERY IMPOR
	   TANT) should contain the standard system error message for what
	   went wrong.	Heres a simple but sufficient example:

	       opendir(D, $dir)     or die "cant opendir $dir: $!";

	  Line up your transliterations when it makes sense:

	       tr [abc]

	  Think about reusability.  Why waste brainpower on a one-shot when
	   you might want to do something like it again?  Consider generaliz
	   ing your code.  Consider writing a module or object class.  Con
	   sider making your code run cleanly with "use strict" and "use warn
	   ings" (or -w) in effect.  Consider giving away your code.  Consider
	   changing your whole world view.  Consider... oh, never mind.

	  Try to document your code and use Pod formatting in a consistent
	   way. Here are commonly expected conventions:

	      use "C<>" for function, variable and module names (and more
	       generally anything that can be considered part of code, like
	       filehandles or specific values). Note that function names are
	       considered more readable with parentheses after their name,
	       that is "function()".

	      use "B<>" for commands names like cat or grep.

	      use "F<>" or "C<>" for file names. "F<>" should be the only Pod
	       code for file names, but as most Pod formatters render it as
	       italic, Unix and Windows paths with their slashes and back
	       slashes may be less readable, and better rendered with "C<>".

	  Be consistent.

	  Be nice.

perl v5.8.8			  2008-04-25			  PERLSTYLE(1)

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