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perlstyle ()
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    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 run your programs under the
         -w flag at all times.  You may turn it off explicitly for
         particular portions of code via the `use 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
         useful.
    
         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 aren't so strong:
    
         o   4-column indent.
    
         o   Opening curly on same line as keyword, if possible,
             otherwise line up.
    
         o   Space before the opening curly of a multi-line BLOCK.
    
         o   One-line BLOCK may be put on one line, including
             curlies.
    
         o   No space before the semicolon.
    
         o   Semicolon omitted in "short" one-line BLOCK.
    
         o   Space around most operators.
    
         o   Space around a "complex" subscript (inside brackets).
    
         o   Blank lines between chunks that do different things.
    
         o   Uncuddled elses.
    
         o   No space between function name and its opening
             parenthesis.
    
         o   Space after each comma.
    
         o   Long lines broken after an operator (except "and" and
             "or").
    
         o   Space after last parenthesis matching on current line.
    
         o   Line up corresponding items vertically.
    
         o   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:
    
         o   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(FOO,$foo) || die "Can't open $foo: $!";
    
             is better than
    
                 die "Can't 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 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.
    
         o   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;
                     }
    
    
         o   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.
    
         o   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.
    
         o   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.
    
         o   Choose mnemonic identifiers.  If you can't remember what
             mnemonic means, you've got a problem.
    
         o   While short identifiers like $gotit are probably ok, use
             underscores to separate words.  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.
    
         o   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.
    
         o   If you have a really hairy regular expression, use the
             `/x' modifier 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.
    
         o   Use the new "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.
    
         o   Use here documents instead of repeated print()
             statements.
    
         o   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: $!";
    
    
         o   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(D, $dir)     or die "can't opendir $dir: $!";
    
    
         o   Line up your transliterations when it makes sense:
    
                 tr [abc]
                    [xyz];
    
    
         o   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'
             (or -w) in effect Consider giving away your code.
             Consider changing your whole world view.  Consider...
             oh, never mind.
    
         o   Be consistent.
    
         o   Be nice.
    
    
    
    


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