perlstyle - Perl style guide |
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 use warnings
pragma or the $^W
variable
if you must. You should
also always run under use strict
or know the reason why not.
The use sigtrap
and even use diagnostics
pragmas may also prove
useful.
Regarding aesthetics of code lay out, about the only thing Larry cares strongly about is that the closing curly bracket of a multi-line BLOCK should line up with the keyword that started the construct. Beyond that, he has other preferences that aren't so strong:
Larry has his reasons for each of these things, but he doesn't claim that everyone else's mind works the same as his does.
Here are some other more substantive style issues to think about:
open(FOO,$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.
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; }
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.
$]
($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.
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.
$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.
/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.
&&
and ||
. Call your subroutines as if they were
functions or list operators to avoid excessive ampersands and parentheses.
print()
statements.
$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: $!";
opendir(D, $dir) or die "can't opendir $dir: $!";
tr [abc] [xyz];
use strict
and use warnings
(or -w) in effect
Consider giving away
your code. Consider changing your whole world view. Consider... oh,
never mind.
perlstyle - Perl style guide |