Amiga Magazin: Amiga-CD 1996 July/AMIGA_1996_7.BIN/ausgabe_7_96/pd-programmierung/perl5_002bin.lha/man/catp/perlsub.0

Text File | 1996-03-02 | 70KB | 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