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Man Page for PERLSTYLE

     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.

     Regarding aesthetics of code lay out, about the only thing
     Larry cares strongly about is that the closing curly brace
     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 multiline BLOCK.

     +   One-line BLOCK may be put on one line, including

     +   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 paren.

     +   Space after each comma.

     +   Long lines broken after an operator (except "and" and

     +   Space after last paren matching on current line.

     +   Line up corresponding items vertically.

     +   Omit redundant punctuation as long as clarity doesn't

     Larry has his reasons for each of these things, but he
     doen't claim that everyone else's mind works the same as his

     Here are some other more substantive style issues to think

     +   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";

         since the main point isn't whether the user typed -v or

         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

         Along the same lines, just because you CAN omit
         parentheses in many places doesn't mean that you ought

             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 parens 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:

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

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

     +   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

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

     +   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.

     +   Use the new "and" and "or" operators to avoid having to
         parenthesize list operators so much, and to reduce the
         incidence of punctuational operators like && and ||.
         Call your subroutines as if they were functions or list
         operators to avoid excessive ampersands and parens.

     +   Use here documents instead of repeated print()

     +   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: $!";

     +   Line up your translations 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 generalizing your code.  Consider
         writing a module or object class.  Consider making your
         code run cleanly with use strict and -w in effect.
         Consider giving away your code.  Consider changing your
         whole world view.  Consider... oh, never mind.

     +   Be consistent.

     +   Be nice.



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