Amiga Tools 5

home *** CD-ROM | disk | FTP | other *** search

/ Amiga Tools 5 / Amiga Tools 5.iso / tools / developer-tools / andere sprachen / perl5 / man / catp / perlsub.0 < prev next >

Wrap

Text File | 1996-03-02 | 68.5 KB | 1,123 lines

PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) NNNNAAAAMMMMEEEE perlsub - Perl subroutines SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS To declare subroutines: ssssuuuubbbb NNNNAAAAMMMMEEEE;;;; #### AAAA """"ffffoooorrrrwwwwaaaarrrrdddd"""" ddddeeeeccccllllaaaarrrraaaattttiiiioooonnnn.... ssssuuuubbbb NNNNAAAAMMMMEEEE((((PPPPRRRROOOOTTTTOOOO))));;;; #### ddddiiiittttttttoooo,,,, bbbbuuuutttt wwwwiiiitttthhhh pppprrrroooottttoooottttyyyyppppeeeessss ssssuuuubbbb NNNNAAAAMMMMEEEE BBBBLLLLOOOOCCCCKKKK #### AAAA ddddeeeeccccllllaaaarrrraaaattttiiiioooonnnn aaaannnndddd aaaa ddddeeeeffffiiiinnnniiiittttiiiioooonnnn.... ssssuuuubbbb NNNNAAAAMMMMEEEE((((PPPPRRRROOOOTTTTOOOO)))) BBBBLLLLOOOOCCCCKKKK #### ddddiiiittttttttoooo,,,, bbbbuuuutttt wwwwiiiitttthhhh pppprrrroooottttoooottttyyyyppppeeeessss To define an anonymous subroutine at runtime: $$$$ssssuuuubbbbrrrreeeeffff ==== ssssuuuubbbb BBBBLLLLOOOOCCCCKKKK;;;; To import subroutines: uuuusssseeee PPPPAAAACCCCKKKKAAAAGGGGEEEE qqqqwwww((((NNNNAAAAMMMMEEEE1111 NNNNAAAAMMMMEEEE2222 NNNNAAAAMMMMEEEE3333))));;;; To call subroutines: NNNNAAAAMMMMEEEE((((LLLLIIIISSSSTTTT))));;;; #### &&&& iiiissss ooooppppttttiiiioooonnnnaaaallll wwwwiiiitttthhhh ppppaaaarrrreeeennnnssss.... NNNNAAAAMMMMEEEE LLLLIIIISSSSTTTT;;;; #### PPPPaaaarrrreeeennnnssss ooooppppttttiiiioooonnnnaaaallll iiiiffff pppprrrreeeeddddeeeeccccllllaaaarrrreeeedddd////iiiimmmmppppoooorrrrtttteeeedddd.... &&&&NNNNAAAAMMMMEEEE;;;; #### PPPPaaaasssssssseeeessss ccccuuuurrrrrrrreeeennnntttt @@@@____ ttttoooo ssssuuuubbbbrrrroooouuuuttttiiiinnnneeee.... DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN Like many languages, Perl provides for user-defined subroutines. These may be located anywhere in the main program, loaded in from other files via the ddddoooo, rrrreeeeqqqquuuuiiiirrrreeee, or uuuusssseeee keywords, or even generated on the fly using eeeevvvvaaaallll or anonymous subroutines (closures). You can even call a function indirectly using a variable containing its name or a CODE reference to it, as in $$$$vvvvaaaarrrr ==== \\\\&&&&ffffuuuunnnnccccttttiiiioooonnnn. The Perl model for function call and return values is simple: all functions are passed as parameters one single flat list of scalars, and all functions likewise return to their caller one single flat list of scalars. Any arrays or hashes in these call and return lists will collapse, losing their identities--but you may always use pass-by- reference instead to avoid this. Both call and return lists may contain as many or as few scalar elements as you'd like. (Often a function without an explicit return statement is called a subroutine, but there's really no difference from the language's perspective.) Any arguments passed to the routine come in as the array @@@@____. Thus if you called a function with two arguments, those would be stored in $$$$____[[[[0000]]]] and $$$$____[[[[1111]]]]. The array @@@@____ is a local array, but its values are implicit references (predating the _p_e_r_l_r_e_f manpage) to the actual scalar parameters. The return value of the subroutine is the 30/Jan/96 perl 5.002 with 1 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) value of the last expression evaluated. Alternatively, a return statement may be used to specify the returned value and exit the subroutine. If you return one or more arrays and/or hashes, these will be flattened together into one large indistinguishable list. Perl does not have named formal parameters, but in practice all you do is assign to a _m_y_(_) list of these. Any variables you use in the function that aren't declared private are global variables. For the gory details on creating private variables, see the sections below on L<"Private Variables via my()"> and the section on _/_"_T_e_m_p_o_r_a_r_y _V_a_l_u_e_s _v_i_a _l_o_c_a_l_(_). To create protected environments for a set of functions in a separate package (and probably a separate file), see the section on _P_a_c_k_a_g_e_s in the _p_e_r_l_m_o_d manpage. Example: ssssuuuubbbb mmmmaaaaxxxx {{{{ mmmmyyyy $$$$mmmmaaaaxxxx ==== sssshhhhiiiifffftttt((((@@@@____))));;;; ffffoooorrrreeeeaaaacccchhhh $$$$ffffoooooooo ((((@@@@____)))) {{{{ $$$$mmmmaaaaxxxx ==== $$$$ffffoooooooo iiiiffff $$$$mmmmaaaaxxxx <<<< $$$$ffffoooooooo;;;; }}}} rrrreeeettttuuuurrrrnnnn $$$$mmmmaaaaxxxx;;;; }}}} $$$$bbbbeeeessssttttddddaaaayyyy ==== mmmmaaaaxxxx(((($$$$mmmmoooonnnn,,,,$$$$ttttuuuueeee,,,,$$$$wwwweeeedddd,,,,$$$$tttthhhhuuuu,,,,$$$$ffffrrrriiii))));;;; Example: #### ggggeeeetttt aaaa lllliiiinnnneeee,,,, ccccoooommmmbbbbiiiinnnniiiinnnngggg ccccoooonnnnttttiiiinnnnuuuuaaaattttiiiioooonnnn lllliiiinnnneeeessss #### tttthhhhaaaatttt ssssttttaaaarrrrtttt wwwwiiiitttthhhh wwwwhhhhiiiitttteeeessssppppaaaacccceeee ssssuuuubbbb ggggeeeetttt____lllliiiinnnneeee {{{{ $$$$tttthhhhiiiisssslllliiiinnnneeee ==== $$$$llllooooooookkkkaaaahhhheeeeaaaadddd;;;; #### GGGGLLLLOOOOBBBBAAAALLLL VVVVAAAARRRRIIIIAAAABBBBLLLLEEEESSSS!!!!!!!! LLLLIIIINNNNEEEE:::: wwwwhhhhiiiilllleeee (((($$$$llllooooooookkkkaaaahhhheeeeaaaadddd ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>)))) {{{{ iiiiffff (((($$$$llllooooooookkkkaaaahhhheeeeaaaadddd ====~~~~ ////^^^^[[[[ \\\\tttt]]]]////)))) {{{{ $$$$tttthhhhiiiisssslllliiiinnnneeee ....==== $$$$llllooooooookkkkaaaahhhheeeeaaaadddd;;;; }}}} eeeellllsssseeee {{{{ llllaaaasssstttt LLLLIIIINNNNEEEE;;;; }}}} }}}} $$$$tttthhhhiiiisssslllliiiinnnneeee;;;; }}}} $$$$llllooooooookkkkaaaahhhheeeeaaaadddd ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; #### ggggeeeetttt ffffiiiirrrrsssstttt lllliiiinnnneeee wwwwhhhhiiiilllleeee (((($$$$____ ==== ggggeeeetttt____lllliiiinnnneeee(((()))))))) {{{{ ............ }}}} Use array assignment to a local list to name your formal arguments: 30/Jan/96 perl 5.002 with 2 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) ssssuuuubbbb mmmmaaaayyyybbbbeeeesssseeeetttt {{{{ mmmmyyyy(((($$$$kkkkeeeeyyyy,,,, $$$$vvvvaaaalllluuuueeee)))) ==== @@@@____;;;; $$$$FFFFoooooooo{{{{$$$$kkkkeeeeyyyy}}}} ==== $$$$vvvvaaaalllluuuueeee uuuunnnnlllleeeessssssss $$$$FFFFoooooooo{{{{$$$$kkkkeeeeyyyy}}}};;;; }}}} This also has the effect of turning call-by-reference into call-by-value, since the assignment copies the values. Otherwise a function is free to do in-place modifications of @@@@____ and change its callers values. uuuuppppccccaaaasssseeee____iiiinnnn(((($$$$vvvv1111,,,, $$$$vvvv2222))));;;; #### tttthhhhiiiissss cccchhhhaaaannnnggggeeeessss $$$$vvvv1111 aaaannnndddd $$$$vvvv2222 ssssuuuubbbb uuuuppppccccaaaasssseeee____iiiinnnn {{{{ ffffoooorrrr ((((@@@@____)))) {{{{ ttttrrrr////aaaa----zzzz////AAAA----ZZZZ//// }}}} }}}} You aren't allowed to modify constants in this way, of course. If an argument were actually literal and you tried to change it, you'd take a (presumably fatal) exception. For example, this won't work: uuuuppppccccaaaasssseeee____iiiinnnn((((""""ffffrrrreeeeddddeeeerrrriiiicccckkkk""""))));;;; It would be much safer if the _u_p_c_a_s_e___i_n_(_) function were written to return a copy of its parameters instead of changing them in place: (((($$$$vvvv3333,,,, $$$$vvvv4444)))) ==== uuuuppppccccaaaasssseeee(((($$$$vvvv1111,,,, $$$$vvvv2222))));;;; #### tttthhhhiiiissss ddddooooeeeessssnnnn''''tttt ssssuuuubbbb uuuuppppccccaaaasssseeee {{{{ mmmmyyyy @@@@ppppaaaarrrrmmmmssss ==== @@@@____;;;; ffffoooorrrr ((((@@@@ppppaaaarrrrmmmmssss)))) {{{{ ttttrrrr////aaaa----zzzz////AAAA----ZZZZ//// }}}} #### wwwwaaaannnnttttaaaarrrrrrrraaaayyyy cccchhhheeeecccckkkkssss iiiiffff wwwweeee wwwweeeerrrreeee ccccaaaalllllllleeeedddd iiiinnnn lllliiiisssstttt ccccoooonnnntttteeeexxxxtttt rrrreeeettttuuuurrrrnnnn wwwwaaaannnnttttaaaarrrrrrrraaaayyyy ???? @@@@ppppaaaarrrrmmmmssss :::: $$$$ppppaaaarrrrmmmmssss[[[[0000]]]];;;; }}}} Notice how this (unprototyped) function doesn't care whether it was passed real scalars or arrays. Perl will see everything as one big long flat @@@@____ parameter list. This is one of the ways where Perl's simple argument- passing style shines. The _u_p_c_a_s_e_(_) function would work perfectly well without changing the _u_p_c_a_s_e_(_) definition even if we fed it things like this: @@@@nnnneeeewwwwlllliiiisssstttt ==== uuuuppppccccaaaasssseeee((((@@@@lllliiiisssstttt1111,,,, @@@@lllliiiisssstttt2222))));;;; @@@@nnnneeeewwwwlllliiiisssstttt ==== uuuuppppccccaaaasssseeee(((( sssspppplllliiiitttt ////::::////,,,, $$$$vvvvaaaarrrr ))));;;; Do not, however, be tempted to do this: ((((@@@@aaaa,,,, @@@@bbbb)))) ==== uuuuppppccccaaaasssseeee((((@@@@lllliiiisssstttt1111,,,, @@@@lllliiiisssstttt2222))));;;; Because like its flat incoming parameter list, the return list is also flat. So all you have managed to do here is stored everything in @@@@aaaa and made @@@@bbbb an empty list. See the section on _/_"_P_a_s_s _b_y _R_e_f_e_r_e_n_c_e for alternatives. 30/Jan/96 perl 5.002 with 3 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) A subroutine may be called using the "&" prefix. The "&" is optional in Perl 5, and so are the parens if the subroutine has been predeclared. (Note, however, that the "&" is _N_O_T optional when you're just naming the subroutine, such as when it's used as an argument to _d_e_f_i_n_e_d_(_) or _u_n_d_e_f_(_). Nor is it optional when you want to do an indirect subroutine call with a subroutine name or reference using the &&&&$$$$ssssuuuubbbbrrrreeeeffff(((()))) or &&&&{{{{$$$$ssssuuuubbbbrrrreeeeffff}}}}(((()))) constructs. See the _p_e_r_l_r_e_f manpage for more on that.) Subroutines may be called recursively. If a subroutine is called using the "&" form, the argument list is optional, and if omitted, no @@@@____ array is set up for the subroutine: the @@@@____ array at the time of the call is visible to subroutine instead. This is an efficiency mechanism that new users may wish to avoid. &&&&ffffoooooooo((((1111,,,,2222,,,,3333))));;;; #### ppppaaaassssssss tttthhhhrrrreeeeeeee aaaarrrrgggguuuummmmeeeennnnttttssss ffffoooooooo((((1111,,,,2222,,,,3333))));;;; #### tttthhhheeee ssssaaaammmmeeee ffffoooooooo(((())));;;; #### ppppaaaassssssss aaaa nnnnuuuullllllll lllliiiisssstttt &&&&ffffoooooooo(((())));;;; #### tttthhhheeee ssssaaaammmmeeee &&&&ffffoooooooo;;;; #### ffffoooooooo(((()))) ggggeeeetttt ccccuuuurrrrrrrreeeennnntttt aaaarrrrggggssss,,,, lllliiiikkkkeeee ffffoooooooo((((@@@@____)))) !!!!!!!! ffffoooooooo;;;; #### lllliiiikkkkeeee ffffoooooooo(((()))) IIIIFFFFFFFF ssssuuuubbbb ffffoooooooo pppprrrreeee----ddddeeeeccccllllaaaarrrreeeedddd,,,, eeeellllsssseeee """"ffffoooooooo"""" Not only does the "&" form make the argument list optional, but it also disables any prototype checking on the arguments you do provide. This is partly for historical reasons, and partly for having a convenient way to cheat if you know what you're doing. See the section on Prototypes below. PPPPrrrriiiivvvvaaaatttteeee VVVVaaaarrrriiiiaaaabbbblllleeeessss vvvviiiiaaaa _m_y_(_) Synopsis: mmmmyyyy $$$$ffffoooooooo;;;; #### ddddeeeeccccllllaaaarrrreeee $$$$ffffoooooooo lllleeeexxxxiiiiccccaaaallllllllyyyy llllooooccccaaaallll mmmmyyyy ((((@@@@wwwwiiiidddd,,,, %%%%ggggeeeetttt))));;;; #### ddddeeeeccccllllaaaarrrreeee lllliiiisssstttt ooooffff vvvvaaaarrrriiiiaaaabbbblllleeeessss llllooooccccaaaallll mmmmyyyy $$$$ffffoooooooo ==== """"fffflllluuuurrrrpppp"""";;;; #### ddddeeeeccccllllaaaarrrreeee $$$$ffffoooooooo lllleeeexxxxiiiiccccaaaallll,,,, aaaannnndddd iiiinnnniiiitttt iiiitttt mmmmyyyy @@@@ooooooooffff ==== @@@@bbbbaaaarrrr;;;; #### ddddeeeeccccllllaaaarrrreeee @@@@ooooooooffff lllleeeexxxxiiiiccccaaaallll,,,, aaaannnndddd iiiinnnniiiitttt iiiitttt A "my" declares the listed variables to be confined (lexically) to the enclosing block, subroutine, eeeevvvvaaaallll, or ddddoooo////rrrreeeeqqqquuuuiiiirrrreeee////uuuusssseeee'd file. If more than one value is listed, the list must be placed in parens. All listed elements must be legal lvalues. Only alphanumeric identifiers may be lexically scoped--magical builtins like $/ must currently be localized with "local" instead. Unlike dynamic variables created by the "local" statement, lexical variables declared with "my" are totally hidden from the outside world, including any called subroutines (even if it's the same subroutine called from itself or 30/Jan/96 perl 5.002 with 4 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) elsewhere--every call gets its own copy). (An _e_v_a_l_(_), however, can see the lexical variables of the scope it is being evaluated in so long as the names aren't hidden by declarations within the _e_v_a_l_(_) itself. See the _p_e_r_l_r_e_f manpage.) The parameter list to _m_y_(_) may be assigned to if desired, which allows you to initialize your variables. (If no initializer is given for a particular variable, it is created with the undefined value.) Commonly this is used to name the parameters to a subroutine. Examples: $$$$aaaarrrrgggg ==== """"ffffrrrreeeedddd"""";;;; #### """"gggglllloooobbbbaaaallll"""" vvvvaaaarrrriiiiaaaabbbblllleeee $$$$nnnn ==== ccccuuuubbbbeeee____rrrrooooooootttt((((22227777))));;;; pppprrrriiiinnnntttt """"$$$$aaaarrrrgggg tttthhhhiiiinnnnkkkkssss tttthhhheeee rrrrooooooootttt iiiissss $$$$nnnn\\\\nnnn"""";;;; ffffrrrreeeedddd tttthhhhiiiinnnnkkkkssss tttthhhheeee rrrrooooooootttt iiiissss 3333 ssssuuuubbbb ccccuuuubbbbeeee____rrrrooooooootttt {{{{ mmmmyyyy $$$$aaaarrrrgggg ==== sssshhhhiiiifffftttt;;;; #### nnnnaaaammmmeeee ddddooooeeeessssnnnn''''tttt mmmmaaaatttttttteeeerrrr $$$$aaaarrrrgggg ********==== 1111////3333;;;; rrrreeeettttuuuurrrrnnnn $$$$aaaarrrrgggg;;;; }}}} The "my" is simply a modifier on something you might assign to. So when you do assign to the variables in its argument list, the "my" doesn't change whether those variables is viewed as a scalar or an array. So mmmmyyyy (((($$$$ffffoooooooo)))) ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; mmmmyyyy @@@@FFFFOOOOOOOO ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; both supply a list context to the righthand side, while mmmmyyyy $$$$ffffoooooooo ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; supplies a scalar context. But the following only declares one variable: mmmmyyyy $$$$ffffoooooooo,,,, $$$$bbbbaaaarrrr ==== 1111;;;; That has the same effect as mmmmyyyy $$$$ffffoooooooo;;;; $$$$bbbbaaaarrrr ==== 1111;;;; The declared variable is not introduced (is not visible) until after the current statement. Thus, mmmmyyyy $$$$xxxx ==== $$$$xxxx;;;; can be used to initialize the new $$$$xxxx with the value of the old $$$$xxxx, and the expression 30/Jan/96 perl 5.002 with 5 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) mmmmyyyy $$$$xxxx ==== 111122223333 aaaannnndddd $$$$xxxx ======== 111122223333 is false unless the old $$$$xxxx happened to have the value 123. Some users may wish to encourage the use of lexically scoped variables. As an aid to catching implicit references to package variables, if you say uuuusssseeee ssssttttrrrriiiicccctttt ''''vvvvaaaarrrrssss'''';;;; then any variable reference from there to the end of the enclosing block must either refer to a lexical variable, or must be fully qualified with the package name. A compilation error results otherwise. An inner block may countermand this with "no strict 'vars'". A _m_y_(_) has both a compile-time and a run-time effect. At compile time, the compiler takes notice of it; the principle usefulness of this is to quiet uuuusssseeee ssssttttrrrriiiicccctttt ''''vvvvaaaarrrrssss''''. The actual initialization doesn't happen until run time, so gets executed every time through a loop. Variables declared with "my" are not part of any package and are therefore never fully qualified with the package name. In particular, you're not allowed to try to make a package variable (or other global) lexical: mmmmyyyy $$$$ppppaaaacccckkkk::::::::vvvvaaaarrrr;;;; #### EEEERRRRRRRROOOORRRR!!!! IIIIlllllllleeeeggggaaaallll ssssyyyynnnnttttaaaaxxxx mmmmyyyy $$$$____;;;; #### aaaallllssssoooo iiiilllllllleeeeggggaaaallll ((((ccccuuuurrrrrrrreeeennnnttttllllyyyy)))) In fact, a dynamic variable (also known as package or global variables) are still accessible using the fully qualified :: notation even while a lexical of the same name is also visible: ppppaaaacccckkkkaaaaggggeeee mmmmaaaaiiiinnnn;;;; llllooooccccaaaallll $$$$xxxx ==== 11110000;;;; mmmmyyyy $$$$xxxx ==== 22220000;;;; pppprrrriiiinnnntttt """"$$$$xxxx aaaannnndddd $$$$::::::::xxxx\\\\nnnn"""";;;; That will print out 20 and 10. You may declare "my" variables at the outer most scope of a file to totally hide any such identifiers from the outside world. This is similar to a C's static variables at the file level. To do this with a subroutine requires the use of a closure (anonymous function). If a block (such as an _e_v_a_l_(_), function, or ppppaaaacccckkkkaaaaggggeeee) wants to create a private subroutine that cannot be called from outside that block, it can declare a lexical variable containing an anonymous sub reference: 30/Jan/96 perl 5.002 with 6 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) mmmmyyyy $$$$sssseeeeccccrrrreeeetttt____vvvveeeerrrrssssiiiioooonnnn ==== ''''1111....000000001111----bbbbeeeettttaaaa'''';;;; mmmmyyyy $$$$sssseeeeccccrrrreeeetttt____ssssuuuubbbb ==== ssssuuuubbbb {{{{ pppprrrriiiinnnntttt $$$$sssseeeeccccrrrreeeetttt____vvvveeeerrrrssssiiiioooonnnn }}}};;;; &&&&$$$$sssseeeeccccrrrreeeetttt____ssssuuuubbbb(((())));;;; As long as the reference is never returned by any function within the module, no outside module can see the subroutine, since its name is not in any package's symbol table. Remember that it's not _R_E_A_L_L_Y called $$$$ssssoooommmmeeee____ppppaaaacccckkkk::::::::sssseeeeccccrrrreeeetttt____vvvveeeerrrrssssiiiioooonnnn or anything; it's just $$$$sssseeeeccccrrrreeeetttt____vvvveeeerrrrssssiiiioooonnnn, unqualified and unqualifiable. This does not work with object methods, however; all object methods have to be in the symbol table of some package to be found. Just because the lexical variable is lexically (also called statically) scoped doesn't mean that within a function it works like a C static. It normally works more like a C auto. But here's a mechanism for giving a function private variables with both lexical scoping and a static lifetime. If you do want to create something like C's static variables, just enclose the whole function in an extra block, and put the static variable outside the function but in the block. {{{{ mmmmyyyy $$$$sssseeeeccccrrrreeeetttt____vvvvaaaallll ==== 0000;;;; ssssuuuubbbb ggggiiiimmmmmmmmeeee____aaaannnnooootttthhhheeeerrrr {{{{ rrrreeeettttuuuurrrrnnnn ++++++++$$$$sssseeeeccccrrrreeeetttt____vvvvaaaallll;;;; }}}} }}}} #### $$$$sssseeeeccccrrrreeeetttt____vvvvaaaallll nnnnoooowwww bbbbeeeeccccoooommmmeeeessss uuuunnnnrrrreeeeaaaacccchhhhaaaabbbblllleeee bbbbyyyy tttthhhheeee oooouuuuttttssssiiiiddddeeee #### wwwwoooorrrrlllldddd,,,, bbbbuuuutttt rrrreeeettttaaaaiiiinnnnssss iiiittttssss vvvvaaaalllluuuueeee bbbbeeeettttwwwweeeeeeeennnn ccccaaaallllllllssss ttttoooo ggggiiiimmmmmmmmeeee____aaaannnnooootttthhhheeeerrrr If this function is being sourced in from a separate file via rrrreeeeqqqquuuuiiiirrrreeee or uuuusssseeee, then this is probably just fine. If it's all in the main program, you'll need to arrange for the _m_y_(_) to be executed early, either by putting the whole block above your pain program, or more likely, merely placing a BEGIN sub around it to make sure it gets executed before your program starts to run: ssssuuuubbbb BBBBEEEEGGGGIIIINNNN {{{{ mmmmyyyy $$$$sssseeeeccccrrrreeeetttt____vvvvaaaallll ==== 0000;;;; ssssuuuubbbb ggggiiiimmmmmmmmeeee____aaaannnnooootttthhhheeeerrrr {{{{ rrrreeeettttuuuurrrrnnnn ++++++++$$$$sssseeeeccccrrrreeeetttt____vvvvaaaallll;;;; }}}} }}}} See the _p_e_r_l_r_u_n manpage about the BEGIN function. 30/Jan/96 perl 5.002 with 7 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) TTTTeeeemmmmppppoooorrrraaaarrrryyyy VVVVaaaalllluuuueeeessss vvvviiiiaaaa _l_o_c_a_l_(_) NNNNOOOOTTTTEEEE: In general, you should be using "my" instead of "local", because it's faster and safer. Execeptions to this include the global punctuation variables, filehandles and formats, and direct manipulation of the Perl symbol table itself. Format variables often use "local" though, as do other variables whose current value must be visible to called subroutines. Synopsis: llllooooccccaaaallll $$$$ffffoooooooo;;;; #### ddddeeeeccccllllaaaarrrreeee $$$$ffffoooooooo ddddyyyynnnnaaaammmmiiiiccccaaaallllllllyyyy llllooooccccaaaallll llllooooccccaaaallll ((((@@@@wwwwiiiidddd,,,, %%%%ggggeeeetttt))));;;; #### ddddeeeeccccllllaaaarrrreeee lllliiiisssstttt ooooffff vvvvaaaarrrriiiiaaaabbbblllleeeessss llllooooccccaaaallll llllooooccccaaaallll $$$$ffffoooooooo ==== """"fffflllluuuurrrrpppp"""";;;; #### ddddeeeeccccllllaaaarrrreeee $$$$ffffoooooooo ddddyyyynnnnaaaammmmiiiicccc,,,, aaaannnndddd iiiinnnniiiitttt iiiitttt llllooooccccaaaallll @@@@ooooooooffff ==== @@@@bbbbaaaarrrr;;;; #### ddddeeeeccccllllaaaarrrreeee @@@@ooooooooffff ddddyyyynnnnaaaammmmiiiicccc,,,, aaaannnndddd iiiinnnniiiitttt iiiitttt llllooooccccaaaallll ****FFFFHHHH;;;; #### llllooooccccaaaalllliiiizzzzeeee $$$$FFFFHHHH,,,, @@@@FFFFHHHH,,,, %%%%FFFFHHHH,,,, &&&&FFFFHHHH ............ llllooooccccaaaallll ****mmmmeeeerrrrllllyyyynnnn ==== ****rrrraaaannnnddddaaaallll;;;; #### nnnnoooowwww $$$$mmmmeeeerrrrllllyyyynnnn iiiissss rrrreeeeaaaallllllllyyyy $$$$rrrraaaannnnddddaaaallll,,,, pppplllluuuussss #### @@@@mmmmeeeerrrrllllyyyynnnn iiiissss rrrreeeeaaaallllllllyyyy @@@@rrrraaaannnnddddaaaallll,,,, eeeettttcccc llllooooccccaaaallll ****mmmmeeeerrrrllllyyyynnnn ==== ''''rrrraaaannnnddddaaaallll'''';;;; #### SSSSAAAAMMMMEEEE TTTTHHHHIIIINNNNGGGG:::: pppprrrroooommmmooootttteeee ''''rrrraaaannnnddddaaaallll'''' ttttoooo ****rrrraaaannnnddddaaaallll llllooooccccaaaallll ****mmmmeeeerrrrllllyyyynnnn ==== \\\\$$$$rrrraaaannnnddddaaaallll;;;; #### jjjjuuuusssstttt aaaalllliiiiaaaassss $$$$mmmmeeeerrrrllllyyyynnnn,,,, nnnnooootttt @@@@mmmmeeeerrrrllllyyyynnnn eeeettttcccc A _l_o_c_a_l_(_) modifies its listed variables to be local to the enclosing block, (or subroutine, eeeevvvvaaaallll{{{{}}}} or ddddoooo) and _t_h_e _a_n_y _c_a_l_l_e_d _f_r_o_m _w_i_t_h_i_n _t_h_a_t _b_l_o_c_k. A _l_o_c_a_l_(_) just gives temporary values to global (meaning package) variables. This is known as dynamic scoping. Lexical scoping is done with "my", which works more like C's auto declarations. If more than one variable is given to _l_o_c_a_l_(_), they must be placed in parens. All listed elements must be legal lvalues. This operator works by saving the current values of those variables in its argument list on a hidden stack and restoring them upon exiting the block, subroutine or eval. This means that called subroutines can also reference the local variable, but not the global one. The argument list may be assigned to if desired, which allows you to initialize your local variables. (If no initializer is given for a particular variable, it is created with an undefined value.) Commonly this is used to name the parameters to a subroutine. Examples: ffffoooorrrr $$$$iiii (((( 0000 ........ 9999 )))) {{{{ $$$$ddddiiiiggggiiiittttssss{{{{$$$$iiii}}}} ==== $$$$iiii;;;; }}}} #### aaaassssssssuuuummmmeeee tttthhhhiiiissss ffffuuuunnnnccccttttiiiioooonnnn uuuusssseeeessss gggglllloooobbbbaaaallll %%%%ddddiiiiggggiiiittttssss hhhhaaaasssshhhh ppppaaaarrrrsssseeee____nnnnuuuummmm(((())));;;; 30/Jan/96 perl 5.002 with 8 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) #### nnnnoooowwww tttteeeemmmmppppoooorrrraaaarrrriiiillllyyyy aaaadddddddd ttttoooo %%%%ddddiiiiggggiiiittttssss hhhhaaaasssshhhh iiiiffff (((($$$$bbbbaaaasssseeee11112222)))) {{{{ #### ((((NNNNOOOOTTTTEEEE:::: nnnnooootttt ccccllllaaaaiiiimmmmiiiinnnngggg tttthhhhiiiissss iiiissss eeeeffffffffiiiicccciiiieeeennnntttt!!!!)))) llllooooccccaaaallll %%%%ddddiiiiggggiiiittttssss ==== ((((%%%%ddddiiiiggggiiiittttssss,,,, ''''tttt'''' ====>>>> 11110000,,,, ''''eeee'''' ====>>>> 11111111))));;;; ppppaaaarrrrsssseeee____nnnnuuuummmm(((())));;;; #### ppppaaaarrrrsssseeee____nnnnuuuummmm ggggeeeettttssss tttthhhhiiiissss nnnneeeewwww %%%%ddddiiiiggggiiiittttssss!!!! }}}} #### oooolllldddd %%%%ddddiiiiggggiiiittttssss rrrreeeessssttttoooorrrreeeedddd hhhheeeerrrreeee Because _l_o_c_a_l_(_) is a run-time command, and so gets executed every time through a loop. In releases of Perl previous to 5.0, this used more stack storage each time until the loop was exited. Perl now reclaims the space each time through, but it's still more efficient to declare your variables outside the loop. A local is simply a modifier on an lvalue expression. When you assign to a localized variable, the local doesn't change whether its list is viewed as a scalar or an array. So llllooooccccaaaallll(((($$$$ffffoooooooo)))) ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; llllooooccccaaaallll @@@@FFFFOOOOOOOO ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; both supply a list context to the righthand side, while llllooooccccaaaallll $$$$ffffoooooooo ==== <<<<SSSSTTTTDDDDIIIINNNN>>>>;;;; supplies a scalar context. PPPPaaaassssssssiiiinnnngggg SSSSyyyymmmmbbbboooollll TTTTaaaabbbblllleeee EEEEnnnnttttrrrriiiieeeessss ((((ttttyyyyppppeeeegggglllloooobbbbssss)))) [Note: The mechanism described in this section was originally the only way to simulate pass-by-reference in older versions of Perl. While it still works fine in modern versions, the new reference mechanism is generally easier to work with. See below.] Sometimes you don't want to pass the value of an array to a subroutine but rather the name of it, so that the subroutine can modify the global copy of it rather than working with a local copy. In perl you can refer to all objects of a particular name by prefixing the name with a star: ****ffffoooooooo. This is often known as a "type glob", since the star on the front can be thought of as a wildcard match for all the funny prefix characters on variables and subroutines and such. When evaluated, the type glob produces a scalar value that represents all the objects of that name, including any filehandle, format or subroutine. When assigned to, it causes the name mentioned to refer to whatever "*" value was assigned to it. Example: 30/Jan/96 perl 5.002 with 9 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) ssssuuuubbbb ddddoooouuuubbbblllleeeeaaaarrrryyyy {{{{ llllooooccccaaaallll((((****ssssoooommmmeeeeaaaarrrryyyy)))) ==== @@@@____;;;; ffffoooorrrreeeeaaaacccchhhh $$$$eeeelllleeeemmmm ((((@@@@ssssoooommmmeeeeaaaarrrryyyy)))) {{{{ $$$$eeeelllleeeemmmm ****==== 2222;;;; }}}} }}}} ddddoooouuuubbbblllleeeeaaaarrrryyyy((((****ffffoooooooo))));;;; ddddoooouuuubbbblllleeeeaaaarrrryyyy((((****bbbbaaaarrrr))));;;; Note that scalars are already passed by reference, so you can modify scalar arguments without using this mechanism by referring explicitly to $$$$____[0] etc. You can modify all the elements of an array by passing all the elements as scalars, but you have to use the * mechanism (or the equivalent reference mechanism) to push, pop or change the size of an array. It will certainly be faster to pass the typeglob (or reference). Even if you don't want to modify an array, this mechanism is useful for passing multiple arrays in a single LIST, since normally the LIST mechanism will merge all the array values so that you can't extract out the individual arrays. For more on typeglobs, see the section on _T_y_p_e_g_l_o_b_s in the _p_e_r_l_d_a_t_a manpage. PPPPaaaassssssss bbbbyyyy RRRReeeeffffeeeerrrreeeennnncccceeee If you want to pass more than one array or hash into a function--or return them from it--and have them maintain their integrity, then you're going to have to use an explicit pass-by-reference. Before you do that, you need to understand references as detailed in the _p_e_r_l_r_e_f manpage. This section may not make much sense to you otherwise. Here are a few simple examples. First, let's pass in several arrays to a function and have it pop all of then, return a new list of all their former last elements: @@@@ttttaaaaiiiilllliiiinnnnggggssss ==== ppppooooppppmmmmaaaannnnyyyy (((( \\\\@@@@aaaa,,,, \\\\@@@@bbbb,,,, \\\\@@@@cccc,,,, \\\\@@@@dddd ))));;;; ssssuuuubbbb ppppooooppppmmmmaaaannnnyyyy {{{{ mmmmyyyy $$$$aaaarrrreeeeffff;;;; mmmmyyyy @@@@rrrreeeettttlllliiiisssstttt ==== (((())));;;; ffffoooorrrreeeeaaaacccchhhh $$$$aaaarrrreeeeffff (((( @@@@____ )))) {{{{ ppppuuuusssshhhh @@@@rrrreeeettttlllliiiisssstttt,,,, ppppoooopppp @@@@$$$$aaaarrrreeeeffff;;;; }}}} rrrreeeettttuuuurrrrnnnn @@@@rrrreeeettttlllliiiisssstttt;;;; }}}} Here's how you might write a function that returns a list of keys occurring in all the hashes passed to it: 30/Jan/96 perl 5.002 with 10 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) @@@@ccccoooommmmmmmmoooonnnn ==== iiiinnnntttteeeerrrr(((( \\\\%%%%ffffoooooooo,,,, \\\\%%%%bbbbaaaarrrr,,,, \\\\%%%%jjjjooooeeee ))));;;; ssssuuuubbbb iiiinnnntttteeeerrrr {{{{ mmmmyyyy (((($$$$kkkk,,,, $$$$hhhhrrrreeeeffff,,,, %%%%sssseeeeeeeennnn))));;;; #### llllooooccccaaaallllssss ffffoooorrrreeeeaaaacccchhhh $$$$hhhhrrrreeeeffff ((((@@@@____)))) {{{{ wwwwhhhhiiiilllleeee (((( $$$$kkkk ==== eeeeaaaacccchhhh %%%%$$$$hhhhrrrreeeeffff )))) {{{{ $$$$sssseeeeeeeennnn{{{{$$$$kkkk}}}}++++++++;;;; }}}} }}}} rrrreeeettttuuuurrrrnnnn ggggrrrreeeepppp {{{{ $$$$sssseeeeeeeennnn{{{{$$$$____}}}} ======== @@@@____ }}}} kkkkeeeeyyyyssss %%%%sssseeeeeeeennnn;;;; }}}} So far, we're just using the normal list return mechanism. What happens if you want to pass or return a hash? Well, if you're only using one of them, or you don't mind them concatenating, then the normal calling convention is ok, although a little expensive. Where people get into trouble is here: ((((@@@@aaaa,,,, @@@@bbbb)))) ==== ffffuuuunnnncccc((((@@@@cccc,,,, @@@@dddd))));;;; oooorrrr ((((%%%%aaaa,,,, %%%%bbbb)))) ==== ffffuuuunnnncccc((((%%%%cccc,,,, %%%%dddd))));;;; That syntax simply won't work. It just sets @@@@aaaa or %%%%aaaa and clears the @@@@bbbb or %%%%bbbb. Plus the function didn't get passed into two separate arrays or hashes: it got one long list in @@@@____, as always. If you can arrange for everyone to deal with this through references, it's cleaner code, although not so nice to look at. Here's a function that takes two array references as arguments, returning the two array elements in order of how many elements they have in them: (((($$$$aaaarrrreeeeffff,,,, $$$$bbbbrrrreeeeffff)))) ==== ffffuuuunnnncccc((((\\\\@@@@cccc,,,, \\\\@@@@dddd))));;;; pppprrrriiiinnnntttt """"@@@@$$$$aaaarrrreeeeffff hhhhaaaassss mmmmoooorrrreeee tttthhhhaaaannnn @@@@$$$$bbbbrrrreeeeffff\\\\nnnn"""";;;; ssssuuuubbbb ffffuuuunnnncccc {{{{ mmmmyyyy (((($$$$ccccrrrreeeeffff,,,, $$$$ddddrrrreeeeffff)))) ==== @@@@____;;;; iiiiffff ((((@@@@$$$$ccccrrrreeeeffff >>>> @@@@$$$$ddddrrrreeeeffff)))) {{{{ rrrreeeettttuuuurrrrnnnn (((($$$$ccccrrrreeeeffff,,,, $$$$ddddrrrreeeeffff))));;;; }}}} eeeellllsssseeee {{{{ rrrreeeettttuuuurrrrnnnn (((($$$$ddddrrrreeeeffff,,,, $$$$ccccrrrreeeeffff))));;;; }}}} }}}} It turns out that you can actually do this also: 30/Jan/96 perl 5.002 with 11 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) ((((****aaaa,,,, ****bbbb)))) ==== ffffuuuunnnncccc((((\\\\@@@@cccc,,,, \\\\@@@@dddd))));;;; pppprrrriiiinnnntttt """"@@@@aaaa hhhhaaaassss mmmmoooorrrreeee tttthhhhaaaannnn @@@@bbbb\\\\nnnn"""";;;; ssssuuuubbbb ffffuuuunnnncccc {{{{ llllooooccccaaaallll ((((****cccc,,,, ****dddd)))) ==== @@@@____;;;; iiiiffff ((((@@@@cccc >>>> @@@@dddd)))) {{{{ rrrreeeettttuuuurrrrnnnn ((((\\\\@@@@cccc,,,, \\\\@@@@dddd))));;;; }}}} eeeellllsssseeee {{{{ rrrreeeettttuuuurrrrnnnn ((((\\\\@@@@dddd,,,, \\\\@@@@cccc))));;;; }}}} }}}} Here we're using the typeglobs to do symbol table aliasing. It's a tad subtle, though, and also won't work if you're using _m_y_(_) variables, since only globals (well, and _l_o_c_a_l_(_)s) are in the symbol table. If you're passing around filehandles, you could usually just use the bare typeglob, like *STDOUT, but typeglobs references would be better because they'll still work properly under uuuusssseeee ssssttttrrrriiiicccctttt ''''rrrreeeeffffssss''''. For example: sssspppplllluuuutttttttteeeerrrr((((\\\\****SSSSTTTTDDDDOOOOUUUUTTTT))));;;; ssssuuuubbbb sssspppplllluuuutttttttteeeerrrr {{{{ mmmmyyyy $$$$ffffhhhh ==== sssshhhhiiiifffftttt;;;; pppprrrriiiinnnntttt $$$$ffffhhhh """"hhhheeeerrrr uuuummmm wwwweeeellllllll aaaa hhhhmmmmmmmmmmmm\\\\nnnn"""";;;; }}}} $$$$rrrreeeecccc ==== ggggeeeetttt____rrrreeeecccc((((\\\\****SSSSTTTTDDDDIIIINNNN))));;;; ssssuuuubbbb ggggeeeetttt____rrrreeeecccc {{{{ mmmmyyyy $$$$ffffhhhh ==== sssshhhhiiiifffftttt;;;; rrrreeeettttuuuurrrrnnnn ssssccccaaaallllaaaarrrr <<<<$$$$ffffhhhh>>>>;;;; }}}} If you're planning on generating new filehandles, you could do this: ssssuuuubbbb ooooppppeeeennnniiiitttt {{{{ mmmmyyyy $$$$nnnnaaaammmmeeee ==== sssshhhhiiiifffftttt;;;; llllooooccccaaaallll ****FFFFHHHH;;;; rrrreeeettttuuuurrrrnnnn ooooppppeeeennnn ((((FFFFHHHH,,,, $$$$ppppaaaatttthhhh)))) ???? \\\\****FFFFHHHH :::: uuuunnnnddddeeeeffff;;;; }}}} Although that will actually produce a small memory leak. See the bottom of the ooooppppeeeennnn(((()))) entry in the _p_e_r_l_f_u_n_c manpage for a somewhat cleaner way using the FileHandle functions supplied with the POSIX package. PPPPrrrroooottttoooottttyyyyppppeeeessss As of the 5.002 release of perl, if you declare ssssuuuubbbb mmmmyyyyppppuuuusssshhhh ((((\\\\@@@@@@@@)))) then _m_y_p_u_s_h_(_) takes arguments exactly like _p_u_s_h_(_) does. 30/Jan/96 perl 5.002 with 12 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) The declaration of the function to be called must be visible at compile time. The prototype only affects the interpretation of new-style calls to the function, where new-style is defined as not using the &&&& character. In other words, if you call it like a builtin function, then it behaves like a builtin function. If you call it like an old-fashioned subroutine, then it behaves like an old- fashioned subroutine. It naturally falls out from this rule that prototypes have no influence on subroutine references like \\\\&&&&ffffoooooooo or on indirect subroutine calls like &&&&{{{{$$$$ssssuuuubbbbrrrreeeeffff}}}}. Method calls are not influenced by prototypes either, because the function to be called is indeterminate at compile time, since it depends on inheritance. Since the intent is primarily to let you define subroutines that work like builtin commands, here are the prototypes for some other functions that parse almost exactly like the corresponding builtins. DDDDeeeeccccllllaaaarrrreeeedddd aaaassss CCCCaaaalllllllleeeedddd aaaassss ssssuuuubbbb mmmmyyyylllliiiinnnnkkkk (((($$$$$$$$)))) mmmmyyyylllliiiinnnnkkkk $$$$oooolllldddd,,,, $$$$nnnneeeewwww ssssuuuubbbb mmmmyyyyvvvveeeecccc (((($$$$$$$$$$$$)))) mmmmyyyyvvvveeeecccc $$$$vvvvaaaarrrr,,,, $$$$ooooffffffffsssseeeetttt,,,, 1111 ssssuuuubbbb mmmmyyyyiiiinnnnddddeeeexxxx (((($$$$$$$$;;;;$$$$)))) mmmmyyyyiiiinnnnddddeeeexxxx &&&&ggggeeeettttssssttttrrrriiiinnnngggg,,,, """"ssssuuuubbbbssssttttrrrr"""" ssssuuuubbbb mmmmyyyyssssyyyysssswwwwrrrriiiitttteeee (((($$$$$$$$$$$$;;;;$$$$)))) mmmmyyyyssssyyyysssswwwwrrrriiiitttteeee $$$$bbbbuuuuffff,,,, 0000,,,, lllleeeennnnggggtttthhhh(((($$$$bbbbuuuuffff)))) ---- $$$$ooooffffffff,,,, $$$$ooooffffffff ssssuuuubbbb mmmmyyyyrrrreeeevvvveeeerrrrsssseeee ((((@@@@)))) mmmmyyyyrrrreeeevvvveeeerrrrsssseeee $$$$aaaa,,,,$$$$bbbb,,,,$$$$cccc ssssuuuubbbb mmmmyyyyjjjjooooiiiinnnn (((($$$$@@@@)))) mmmmyyyyjjjjooooiiiinnnn """"::::"""",,,,$$$$aaaa,,,,$$$$bbbb,,,,$$$$cccc ssssuuuubbbb mmmmyyyyppppoooopppp ((((\\\\@@@@)))) mmmmyyyyppppoooopppp @@@@aaaarrrrrrrraaaayyyy ssssuuuubbbb mmmmyyyysssspppplllliiiicccceeee ((((\\\\@@@@$$$$$$$$@@@@)))) mmmmyyyysssspppplllliiiicccceeee @@@@aaaarrrrrrrraaaayyyy,,,,@@@@aaaarrrrrrrraaaayyyy,,,,0000,,,,@@@@ppppuuuusssshhhhmmmmeeee ssssuuuubbbb mmmmyyyykkkkeeeeyyyyssss ((((\\\\%%%%)))) mmmmyyyykkkkeeeeyyyyssss %%%%{{{{$$$$hhhhaaaasssshhhhrrrreeeeffff}}}} ssssuuuubbbb mmmmyyyyooooppppeeeennnn ((((****;;;;$$$$)))) mmmmyyyyooooppppeeeennnn HHHHAAAANNNNDDDDLLLLEEEE,,,, $$$$nnnnaaaammmmeeee ssssuuuubbbb mmmmyyyyppppiiiippppeeee ((((********)))) mmmmyyyyppppiiiippppeeee RRRREEEEAAAADDDDHHHHAAAANNNNDDDDLLLLEEEE,,,, WWWWRRRRIIIITTTTEEEEHHHHAAAANNNNDDDDLLLLEEEE ssssuuuubbbb mmmmyyyyggggrrrreeeepppp ((((&&&&@@@@)))) mmmmyyyyggggrrrreeeepppp {{{{ ////ffffoooooooo//// }}}} $$$$aaaa,,,,$$$$bbbb,,,,$$$$cccc ssssuuuubbbb mmmmyyyyrrrraaaannnndddd (((($$$$)))) mmmmyyyyrrrraaaannnndddd 44442222 ssssuuuubbbb mmmmyyyyttttiiiimmmmeeee (((()))) mmmmyyyyttttiiiimmmmeeee Any backslashed prototype character represents an actual argument that absolutely must start with that character. Unbackslashed prototype characters have special meanings. Any unbackslashed @ or % eats all the rest of the arguments, and forces list context. An argument represented by $ forces scalar context. An & requires an anonymous subroutine, which, if passed as the first argument, does not require the "sub" keyword or a subsequent comma. A * does whatever it has to do to turn the argument into a reference to a symbol table entry. A semicolon separates mandatory arguments from optional arguments. (It is redundant before @ or %.) Note how the last three examples above are treated 30/Jan/96 perl 5.002 with 13 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) specially by the parser. _m_y_g_r_e_p_(_) is parsed as a true list operator, _m_y_r_a_n_d_(_) is parsed as a true unary operator with unary precedence the same as _r_a_n_d_(_), and _m_y_t_i_m_e_(_) is truly argumentless, just like _t_i_m_e_(_). That is, if you say mmmmyyyyttttiiiimmmmeeee ++++2222;;;; you'll get _m_y_t_i_m_e_(_) + 2, not _m_y_t_i_m_e(2), which is how it would be parsed without the prototype. The interesting thing about & is that you can generate new syntax with it: ssssuuuubbbb ttttrrrryyyy ((((&&&&$$$$)))) {{{{ mmmmyyyy(((($$$$ttttrrrryyyy,,,,$$$$ccccaaaattttcccchhhh)))) ==== @@@@____;;;; eeeevvvvaaaallll {{{{ &&&&$$$$ttttrrrryyyy }}}};;;; iiiiffff (((($$$$@@@@)))) {{{{ llllooooccccaaaallll $$$$____ ==== $$$$@@@@;;;; &&&&$$$$ccccaaaattttcccchhhh;;;; }}}} }}}} ssssuuuubbbb ccccaaaattttcccchhhh ((((&&&&)))) {{{{ @@@@____ }}}} ttttrrrryyyy {{{{ ddddiiiieeee """"pppphhhhooooooooeeeeyyyy"""";;;; }}}} ccccaaaattttcccchhhh {{{{ ////pppphhhhooooooooeeeeyyyy//// aaaannnndddd pppprrrriiiinnnntttt """"uuuunnnnpppphhhhooooooooeeeeyyyy\\\\nnnn"""";;;; }}}};;;; That prints "unphooey". (Yes, there are still unresolved issues having to do with the visibility of @@@@____. I'm ignoring that question for the moment. (But note that if we make @@@@____ lexically scoped, those anonymous subroutines can act like closures... (Gee, is this sounding a little Lispish? (Nevermind.)))) And here's a reimplementation of grep: ssssuuuubbbb mmmmyyyyggggrrrreeeepppp ((((&&&&@@@@)))) {{{{ mmmmyyyy $$$$ccccooooddddeeee ==== sssshhhhiiiifffftttt;;;; mmmmyyyy @@@@rrrreeeessssuuuulllltttt;;;; ffffoooorrrreeeeaaaacccchhhh $$$$____ ((((@@@@____)))) {{{{ ppppuuuusssshhhh((((@@@@rrrreeeessssuuuulllltttt,,,, $$$$____)))) iiiiffff &&&&$$$$rrrreeeeffff;;;; }}}} @@@@rrrreeeessssuuuulllltttt;;;; }}}} Some folks would prefer full alphanumeric prototypes. Alphanumerics have been intentionally left out of prototypes for the express purpose of someday in the future adding named, formal parameters. The current mechanism's main goal is to let module writers provide better diagnostics for module users. Larry feels the notation quite understandable to Perl programmers, and 30/Jan/96 perl 5.002 with 14 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) that it will not intrude greatly upon the meat of the module, nor make it harder to read. The line noise is visually encapsulated into a small pill that's easy to swallow. It's probably best to prototype new functions, not retrofit prototyping into older ones. That's because you must be especially careful about silent impositions of differing list versus scalar contexts. For example, if you decide that a function should take just one parameter, like this: ssssuuuubbbb ffffuuuunnnncccc (((($$$$)))) {{{{ mmmmyyyy $$$$nnnn ==== sssshhhhiiiifffftttt;;;; pppprrrriiiinnnntttt """"yyyyoooouuuu ggggaaaavvvveeee mmmmeeee $$$$nnnn\\\\nnnn"""";;;; }}}} and someone has been calling it with an array or expression returning a list: ffffuuuunnnncccc((((@@@@ffffoooooooo))));;;; ffffuuuunnnncccc(((( sssspppplllliiiitttt ////:::://// ))));;;; Then you've just supplied an automatic _s_c_a_l_a_r_(_) in front of their argument, which can be more than a bit surprising. The old @@@@ffffoooooooo which used to hold one thing doesn't get passed in. Instead, the _f_u_n_c_(_) now gets passed in 1, that is, the number of elments in @@@@ffffoooooooo. And the _s_p_l_i_t_(_) gets called in a scalar context and starts scribbling on your @@@@____ parameter list. This is all very powerful, of course, and should only be used in moderation to make the world a better place. OOOOvvvveeeerrrrrrrriiiiddddiiiinnnngggg BBBBuuuuiiiillllttttiiiinnnn FFFFuuuunnnnccccttttiiiioooonnnnssss Many builtin functions may be overridden, though this should only be tried occasionally and for good reason. Typically this might be done by a package attempting to emulate missing builtin functionality on a non-Unix system. Overriding may only be done by importing the name from a module--ordinary predeclaration isn't good enough. However, the ssssuuuubbbbssss pragma (compiler directive) lets you, in effect, predeclare subs via the import syntax, and these names may then override the builtin ones: uuuusssseeee ssssuuuubbbbssss ''''cccchhhhddddiiiirrrr'''',,,, ''''cccchhhhrrrrooooooootttt'''',,,, ''''cccchhhhmmmmoooodddd'''',,,, ''''cccchhhhoooowwwwnnnn'''';;;; cccchhhhddddiiiirrrr $$$$ssssoooommmmeeeewwwwhhhheeeerrrreeee;;;; ssssuuuubbbb cccchhhhddddiiiirrrr {{{{ ............ }}}} Library modules should not in general export builtin names like "open" or "chdir" as part of their default @@@@EEEEXXXXPPPPOOOORRRRTTTT 30/Jan/96 perl 5.002 with 15 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) list, since these may sneak into someone else's namespace and change the semantics unexpectedly. Instead, if the module adds the name to the @@@@EEEEXXXXPPPPOOOORRRRTTTT____OOOOKKKK list, then it's possible for a user to import the name explicitly, but not implicitly. That is, they could say uuuusssseeee MMMMoooodddduuuulllleeee ''''ooooppppeeeennnn'''';;;; and it would import the open override, but if they said uuuusssseeee MMMMoooodddduuuulllleeee;;;; they would get the default imports without the overrides. AAAAuuuuttttoooollllooooaaaaddddiiiinnnngggg If you call a subroutine that is undefined, you would ordinarily get an immediate fatal error complaining that the subroutine doesn't exist. (Likewise for subroutines being used as methods, when the method doesn't exist in any of the base classes of the class package.) If, however, there is an AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD subroutine defined in the package or packages that were searched for the original subroutine, then that AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD subroutine is called with the arguments that would have been passed to the original subroutine. The fully qualified name of the original subroutine magically appears in the $$$$AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD variable in the same package as the AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD routine. The name is not passed as an ordinary argument because, er, well, just because, that's why... Most AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD routines will load in a definition for the subroutine in question using eval, and then execute that subroutine using a special form of "goto" that erases the stack frame of the AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD routine without a trace. (See the standard AAAAuuuuttttooooLLLLooooaaaaddddeeeerrrr module, for example.) But an AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD routine can also just emulate the routine and never define it. For example, let's pretend that a function that wasn't defined should just call _s_y_s_t_e_m_(_) with those arguments. All you'd do is this: ssssuuuubbbb AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD {{{{ mmmmyyyy $$$$pppprrrrooooggggrrrraaaammmm ==== $$$$AAAAUUUUTTTTOOOOLLLLOOOOAAAADDDD;;;; $$$$pppprrrrooooggggrrrraaaammmm ====~~~~ ssss////....****::::::::////////;;;; ssssyyyysssstttteeeemmmm(((($$$$pppprrrrooooggggrrrraaaammmm,,,, @@@@____))));;;; }}}} ddddaaaatttteeee(((())));;;; wwwwhhhhoooo((((''''aaaammmm'''',,,, iiii''''))));;;; llllssss((((''''----llll''''))));;;; In fact, if you preclare the functions you want to call that way, you don't even need the parentheses: 30/Jan/96 perl 5.002 with 16 PERLSUB(1) User Contributed Perl Documentation PERLSUB(1) uuuusssseeee ssssuuuubbbbssss qqqqwwww((((ddddaaaatttteeee wwwwhhhhoooo llllssss))));;;; ddddaaaatttteeee;;;; wwwwhhhhoooo """"aaaammmm"""",,,, """"iiii"""";;;; llllssss ----llll;;;; A more complete example of this is the standard Shell module, which can treat undefined subroutine calls as calls to Unix programs. Mechanisms are available for modules writers to help split the modules up into autoloadable files. See the standard AutoLoader module described in the _A_u_t_o_l_o_a_d_e_r manpage, the standard SelfLoader modules in the _S_e_l_f_L_o_a_d_e_r manpage, and the document on adding C functions to perl code in the _p_e_r_l_x_s manpage. SSSSEEEEEEEE AAAALLLLSSSSOOOO See the _p_e_r_l_r_e_f manpage for more on references. See the _p_e_r_l_x_s manpage if you'd like to learn about calling C subroutines from perl. See the _p_e_r_l_m_o_d manpage to learn about bundling up your functions in separate files. 30/Jan/96 perl 5.002 with 17