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Text File | 1996-03-02 | 14.8 KB | 331 lines

PERLSTYLE(1) User Contributed Perl Documentation PERLSTYLE(1) NNNNAAAAMMMMEEEE perlstyle - Perl style guide DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN 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 ----wwww flag at all times. You may turn it off explicitly for particular portions of code via the $$$$^^^^WWWW variable if you must. You should also always run under uuuusssseeee ssssttttrrrriiiicccctttt or know the reason why not. The <use sigtrap> and even <use diagnostics> pragmas may also prove useful. Regarding aesthetics of code lay out, about the only thing Larry cares strongly about is that the closing curly brace of a multi-line BLOCK should line up with the keyword that started the construct. Beyond that, he has other preferences that aren't so strong: +o 4-column indent. +o Opening curly on same line as keyword, if possible, otherwise line up. +o Space before the opening curly of a multiline BLOCK. +o One-line BLOCK may be put on one line, including curlies. +o No space before the semicolon. +o Semicolon omitted in "short" one-line BLOCK. +o Space around most operators. +o Space around a "complex" subscript (inside brackets). +o Blank lines between chunks that do different things. +o Uncuddled elses. +o No space between function name and its opening paren. +o Space after each comma. +o Long lines broken after an operator (except "and" and "or"). +o Space after last paren matching on current line. 30/Jan/96 perl 5.002 with 1 PERLSTYLE(1) User Contributed Perl Documentation PERLSTYLE(1) +o Line up corresponding items vertically. +o Omit redundant punctuation as long as clarity doesn't suffer. Larry has his reasons for each of these things, but he doen't claim that everyone else's mind works the same as his does. Here are some other more substantive style issues to think about: +o Just because you _C_A_N do something a particular way doesn't mean that you _S_H_O_U_L_D do it that way. Perl is designed to give you several ways to do anything, so consider picking the most readable one. For instance ooooppppeeeennnn((((FFFFOOOOOOOO,,,,$$$$ffffoooooooo)))) |||||||| ddddiiiieeee """"CCCCaaaannnn''''tttt ooooppppeeeennnn $$$$ffffoooooooo:::: $$$$!!!!"""";;;; is better than ddddiiiieeee """"CCCCaaaannnn''''tttt ooooppppeeeennnn $$$$ffffoooooooo:::: $$$$!!!!"""" uuuunnnnlllleeeessssssss ooooppppeeeennnn((((FFFFOOOOOOOO,,,,$$$$ffffoooooooo))));;;; because the second way hides the main point of the statement in a modifier. On the other hand pppprrrriiiinnnntttt """"SSSSttttaaaarrrrttttiiiinnnngggg aaaannnnaaaallllyyyyssssiiiissss\\\\nnnn"""" iiiiffff $$$$vvvveeeerrrrbbbboooosssseeee;;;; is better than $$$$vvvveeeerrrrbbbboooosssseeee &&&&&&&& pppprrrriiiinnnntttt """"SSSSttttaaaarrrrttttiiiinnnngggg aaaannnnaaaallllyyyyssssiiiissss\\\\nnnn"""";;;; since the main point isn't whether the user typed ----vvvv or not. Similarly, just because an operator lets you assume default arguments doesn't mean that you have to make use of the defaults. The defaults are there for lazy systems programmers writing one-shot programs. If you want your program to be readable, consider supplying the argument. Along the same lines, just because you _C_A_N omit parentheses in many places doesn't mean that you ought to: rrrreeeettttuuuurrrrnnnn pppprrrriiiinnnntttt rrrreeeevvvveeeerrrrsssseeee ssssoooorrrrtttt nnnnuuuummmm vvvvaaaalllluuuueeeessss %%%%aaaarrrrrrrraaaayyyy;;;; rrrreeeettttuuuurrrrnnnn pppprrrriiiinnnntttt((((rrrreeeevvvveeeerrrrsssseeee((((ssssoooorrrrtttt nnnnuuuummmm ((((vvvvaaaalllluuuueeeessss((((%%%%aaaarrrrrrrraaaayyyy))))))))))))))));;;; When in doubt, parenthesize. At the very least it will let some poor schmuck bounce on the % key in vvvviiii. Even if you aren't in doubt, consider the mental welfare of the person who has to maintain the code 30/Jan/96 perl 5.002 with 2 PERLSTYLE(1) User Contributed Perl Documentation PERLSTYLE(1) after you, and who will probably put parens in the wrong place. +o Don't go through silly contortions to exit a loop at the top or the bottom, when Perl provides the llllaaaasssstttt operator so you can exit in the middle. Just "outdent" it a little to make it more visible: LLLLIIIINNNNEEEE:::: ffffoooorrrr ((((;;;;;;;;)))) {{{{ ssssttttaaaatttteeeemmmmeeeennnnttttssss;;;; llllaaaasssstttt LLLLIIIINNNNEEEE iiiiffff $$$$ffffoooooooo;;;; nnnneeeexxxxtttt LLLLIIIINNNNEEEE iiiiffff ////^^^^####////;;;; ssssttttaaaatttteeeemmmmeeeennnnttttssss;;;; }}}} +o Don't be afraid to use loop labels--they're there to enhance readability as well as to allow multi-level loop breaks. See the previous example. +o Avoid using _g_r_e_p_(_) (or _m_a_p_(_)) or `backticks` in a void context, that is, when you just throw away their return values. Those functions all have return values, so use them. Otherwise use a _f_o_r_e_a_c_h_(_) loop or the _s_y_s_t_e_m_(_) function instead. +o For portability, when using features that may not be implemented on every machine, test the construct in an eval to see if it fails. If you know what version or patchlevel a particular feature was implemented, you can test $$$$]]]] ($PERL_VERSION in EEEEnnnngggglllliiiisssshhhh) to see if it will be there. The CCCCoooonnnnffffiiiigggg module will also let you interrogate values determined by the CCCCoooonnnnffffiiiigggguuuurrrreeee program when Perl was installed. +o Choose mnemonic identifiers. If you can't remember what mnemonic means, you've got a problem. +o While short identifiers like $$$$ggggoooottttiiiitttt are probably ok, use underscores to separate words. It is generally easier to read $$$$vvvvaaaarrrr____nnnnaaaammmmeeeessss____lllliiiikkkkeeee____tttthhhhiiiissss than $$$$VVVVaaaarrrrNNNNaaaammmmeeeessssLLLLiiiikkkkeeeeTTTThhhhiiiissss, especially for non-native speakers of English. It's also a simple rule that works consistently with VAR_NAMES_LIKE_THIS. Package names are sometimes an exception to this rule. Perl informally reserves lowercase module names for "pragma" modules like iiiinnnntttteeeeggggeeeerrrr and ssssttttrrrriiiicccctttt. Other modules should begin with a capital letter and use mixed case, but probably without underscores due to limitations in primitive filesystems' representations of module names as files that must fit into a few sparse bites. 30/Jan/96 perl 5.002 with 3 PERLSTYLE(1) User Contributed Perl Documentation PERLSTYLE(1) +o You may find it helpful to use letter case to indicate the scope or nature of a variable. For example: $$$$AAAALLLLLLLL____CCCCAAAAPPPPSSSS____HHHHEEEERRRREEEE ccccoooonnnnssssttttaaaannnnttttssss oooonnnnllllyyyy ((((bbbbeeeewwwwaaaarrrreeee ccccllllaaaasssshhhheeeessss wwwwiiiitttthhhh ppppeeeerrrrllll vvvvaaaarrrrssss!!!!)))) $$$$SSSSoooommmmeeee____CCCCaaaappppssss____HHHHeeeerrrreeee ppppaaaacccckkkkaaaaggggeeee----wwwwiiiiddddeeee gggglllloooobbbbaaaallll////ssssttttaaaattttiiiicccc $$$$nnnnoooo____ccccaaaappppssss____hhhheeeerrrreeee ffffuuuunnnnccccttttiiiioooonnnn ssssccccooooppppeeee mmmmyyyy(((()))) oooorrrr llllooooccccaaaallll(((()))) vvvvaaaarrrriiiiaaaabbbblllleeeessss Function and method names seem to work best as all lowercase. E.g., $$$$oooobbbbjjjj->_a_s___s_t_r_i_n_g_(_). You can use a leading underscore to indicate that a variable or function should not be used outside the package that defined it. +o If you have a really hairy regular expression, use the ////xxxx modifier and put in some whitespace to make it look a little less like line noise. Don't use slash as a delimiter when your regexp has slashes or backslashes. +o Use the new "and" and "or" operators to avoid having to parenthesize list operators so much, and to reduce the incidence of punctuational operators like &&&&&&&& and ||||||||. Call your subroutines as if they were functions or list operators to avoid excessive ampersands and parens. +o Use here documents instead of repeated _p_r_i_n_t_(_) statements. +o Line up corresponding things vertically, especially if it'd be too long to fit on one line anyway. $$$$IIIIDDDDXXXX ==== $$$$SSSSTTTT____MMMMTTTTIIIIMMMMEEEE;;;; $$$$IIIIDDDDXXXX ==== $$$$SSSSTTTT____AAAATTTTIIIIMMMMEEEE iiiiffff $$$$oooopppptttt____uuuu;;;; $$$$IIIIDDDDXXXX ==== $$$$SSSSTTTT____CCCCTTTTIIIIMMMMEEEE iiiiffff $$$$oooopppptttt____cccc;;;; $$$$IIIIDDDDXXXX ==== $$$$SSSSTTTT____SSSSIIIIZZZZEEEE iiiiffff $$$$oooopppptttt____ssss;;;; mmmmkkkkddddiiiirrrr $$$$ttttmmmmppppddddiiiirrrr,,,, 0000777700000000 oooorrrr ddddiiiieeee """"ccccaaaannnn''''tttt mmmmkkkkddddiiiirrrr $$$$ttttmmmmppppddddiiiirrrr:::: $$$$!!!!"""";;;; cccchhhhddddiiiirrrr(((($$$$ttttmmmmppppddddiiiirrrr)))) oooorrrr ddddiiiieeee """"ccccaaaannnn''''tttt cccchhhhddddiiiirrrr $$$$ttttmmmmppppddddiiiirrrr:::: $$$$!!!!"""";;;; mmmmkkkkddddiiiirrrr ''''ttttmmmmpppp'''',,,, 0000777777777777 oooorrrr ddddiiiieeee """"ccccaaaannnn''''tttt mmmmkkkkddddiiiirrrr $$$$ttttmmmmppppddddiiiirrrr////ttttmmmmpppp:::: $$$$!!!!"""";;;; +o Always check the return codes of system calls. Good error messages should go to STDERR, include which program caused the problem, what the failed system call and arguments were, and VERY IMPORTANT) should contain the standard system error message for what went wrong. Here's a simple but sufficient example: ooooppppeeeennnnddddiiiirrrr((((DDDD,,,, $$$$ddddiiiirrrr)))) oooorrrr ddddiiiieeee """"ccccaaaannnn''''tttt ooooppppeeeennnnddddiiiirrrr $$$$ddddiiiirrrr:::: $$$$!!!!"""";;;; +o Line up your translations when it makes sense: 30/Jan/96 perl 5.002 with 4 PERLSTYLE(1) User Contributed Perl Documentation PERLSTYLE(1) ttttrrrr [[[[aaaabbbbcccc]]]] [[[[xxxxyyyyzzzz]]]];;;; +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 uuuusssseeee ssssttttrrrriiiicccctttt and ----wwww in effect. Consider giving away your code. Consider changing your whole world view. Consider... oh, never mind. +o Be consistent. +o Be nice. 30/Jan/96 perl 5.002 with 5