NAME

       perlstyle - Perl style guide

DESCRIPTION

       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 use strict and warnings in all your code or know the reason
       why not to.  You may turn them off explicitly for particular portions of code via "no
       warnings" or "no strict", and this can be limited to the specific warnings or strict
       features you wish to disable.  The -w flag and $^W variable should not be used for this
       purpose since they can affect code you use but did not write, such as modules from core or
       CPAN.

       A concise way to arrange for this is to use the "use VERSION" syntax, requesting a version
       5.36 or above, which will enable both the "strict" and "warnings" pragmata (as well as
       several other useful named features).

           use v5.36;

       Regarding aesthetics of code layout, 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 aren't so strong:

       •   4-column indent.

       •   Opening curly on same line as keyword, if possible, otherwise line up.

       •   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 doesn't suffer.

       Larry has his reasons for each of these things, but he doesn't claim that everyone else's
       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 doesn't mean that you SHOULD do it
           that way.  Perl is designed to give you several ways to do anything, so consider
           picking the most readable one.  For instance

               open(my $fh, '<', $foo) || die "Can't open $foo: $!";

           is better than

               die "Can't open $foo: $!" unless open(my $fh, '<', $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 isn't whether the user typed -v or not.

           Similarly, just because an operator lets you assume default arguments doesn't 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 supplying the argument.

           Along the same lines, just because you CAN omit parentheses in many places doesn't
           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 aren't in doubt, consider the mental welfare of the person who has to
           maintain the code after you, and who will probably put parentheses in the wrong place.

       •   Don't 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:

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

       •   Don't be afraid to use loop labels--they're there to enhance readability as well as to
           allow multilevel loop breaks.  See the previous example.

       •   Avoid using grep() (or map()) or `backticks` in a void context, that is, when you just
           throw away their return values.  Those functions all have return values, so use them.
           Otherwise use a foreach() 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
           interrogate values determined by the Configure program when Perl was installed.

       •   Choose mnemonic identifiers.  If you can't remember what mnemonic means, you've got a
           problem.

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

           Package names are sometimes an exception to this rule.  Perl informally 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"  or "/xx" modifiers and
           put in some whitespace to make it look a little less like line noise.  Don't use slash
           as a delimiter when your regexp has slashes or backslashes.

       •   Use the "and" and "or" operators to avoid having to parenthesize list operators so
           much, and to reduce the incidence of punctuation 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 it'd 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 "can't mkdir $tmpdir: $!";
               chdir($tmpdir)      or die "can't chdir $tmpdir: $!";
               mkdir 'tmp',   0777 or die "can't 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 IMPORTANT) should contain the standard system error message
           for what went wrong.  Here's a simple but sufficient example:

               opendir(my $dh, $dir)        or die "can't opendir $dir: $!";

       •   Line up your transliterations when it makes sense:

               tr [abc]
                  [xyz];

       •   Think about reusability.  Why waste brainpower on a one-shot when you might want to do
           something like it again?  Consider generalizing your code.  Consider writing a module
           or object class.  Consider making your code run cleanly with "use strict" and "use
           warnings" 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 backslashes may be less readable, and better rendered with
               "C<>".

       •   Be consistent.

       •   Be nice.