PERLSTYLE(1)PERLSTYLE(1)NAMEperlstyle - Perl style guide
DESCRIPTION
Style
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 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 paren.
· Space after each comma.
· Long lines broken after an operator (except "and" and "or").
· Space after last paren 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 doen'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(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 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 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:
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 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 installed.
· 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() 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: $!";
· Line up your translations 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 -w in
effect. Consider giving away your code. Consider changing your
whole world view. Consider... oh, never mind.
· Be consistent.
· Be nice.
3rd Berkeley DistributionPERLSTYLE(1)
