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diff --git a/Master/tlpkg/tlperl.straw/lib/pods/perlcompile.pod b/Master/tlpkg/tlperl.straw/lib/pods/perlcompile.pod new file mode 100755 index 00000000000..505ce68384f --- /dev/null +++ b/Master/tlpkg/tlperl.straw/lib/pods/perlcompile.pod @@ -0,0 +1,293 @@ +=head1 NAME + +perlcompile - Introduction to the Perl Compiler-Translator + +=head1 DESCRIPTION + +Perl has always had a compiler: your source is compiled into an +internal form (a parse tree) which is then optimized before being +run. Since version 5.005, Perl has shipped with a module +capable of inspecting the optimized parse tree (C<B>), and this has +been used to write many useful utilities, including a module that lets +you turn your Perl into C source code that can be compiled into a +native executable. + +The C<B> module provides access to the parse tree, and other modules +("back ends") do things with the tree. Some write it out as +semi-human-readable text. Another traverses the parse tree to build a +cross-reference of which subroutines, formats, and variables are used +where. Another checks your code for dubious constructs. Yet another back +end dumps the parse tree back out as Perl source, acting as a source code +beautifier or deobfuscator. + +Because its original purpose was to be a way to produce C code +corresponding to a Perl program, and in turn a native executable, the +C<B> module and its associated back ends are known as "the +compiler", even though they don't really compile anything. +Different parts of the compiler are more accurately a "translator", +or an "inspector", but people want Perl to have a "compiler +option" not an "inspector gadget". What can you do? + +This document covers the use of the Perl compiler: which modules +it comprises, how to use the most important of the back end modules, +what problems there are, and how to work around them. + +=head2 Layout + +The compiler back ends are in the C<B::> hierarchy, and the front-end +(the module that you, the user of the compiler, will sometimes +interact with) is the O module. + +Here are the important back ends to know about, with their status +expressed as a number from 0 (outline for later implementation) to +10 (if there's a bug in it, we're very surprised): + +=over 4 + +=item B::Lint + +Complains if it finds dubious constructs in your source code. Status: +6 (it works adequately, but only has a very limited number of areas +that it checks). + +=item B::Deparse + +Recreates the Perl source, making an attempt to format it coherently. +Status: 8 (it works nicely, but a few obscure things are missing). + +=item B::Xref + +Reports on the declaration and use of subroutines and variables. +Status: 8 (it works nicely, but still has a few lingering bugs). + +=back + +=head1 Using The Back Ends + +The following sections describe how to use the various compiler back +ends. They're presented roughly in order of maturity, so that the +most stable and proven back ends are described first, and the most +experimental and incomplete back ends are described last. + +The O module automatically enabled the B<-c> flag to Perl, which +prevents Perl from executing your code once it has been compiled. +This is why all the back ends print: + + myperlprogram syntax OK + +before producing any other output. + +=head2 The Cross Referencing Back End + +The cross referencing back end (B::Xref) produces a report on your program, +breaking down declarations and uses of subroutines and variables (and +formats) by file and subroutine. For instance, here's part of the +report from the I<pod2man> program that comes with Perl: + + Subroutine clear_noremap + Package (lexical) + $ready_to_print i1069, 1079 + Package main + $& 1086 + $. 1086 + $0 1086 + $1 1087 + $2 1085, 1085 + $3 1085, 1085 + $ARGV 1086 + %HTML_Escapes 1085, 1085 + +This shows the variables used in the subroutine C<clear_noremap>. The +variable C<$ready_to_print> is a my() (lexical) variable, +B<i>ntroduced (first declared with my()) on line 1069, and used on +line 1079. The variable C<$&> from the main package is used on 1086, +and so on. + +A line number may be prefixed by a single letter: + +=over 4 + +=item i + +Lexical variable introduced (declared with my()) for the first time. + +=item & + +Subroutine or method call. + +=item s + +Subroutine defined. + +=item r + +Format defined. + +=back + +The most useful option the cross referencer has is to save the report +to a separate file. For instance, to save the report on +I<myperlprogram> to the file I<report>: + + $ perl -MO=Xref,-oreport myperlprogram + +=head2 The Decompiling Back End + +The Deparse back end turns your Perl source back into Perl source. It +can reformat along the way, making it useful as a deobfuscator. The +most basic way to use it is: + + $ perl -MO=Deparse myperlprogram + +You'll notice immediately that Perl has no idea of how to paragraph +your code. You'll have to separate chunks of code from each other +with newlines by hand. However, watch what it will do with +one-liners: + + $ perl -MO=Deparse -e '$op=shift||die "usage: $0 + code [...]";chomp(@ARGV=<>)unless@ARGV; for(@ARGV){$was=$_;eval$op; + die$@ if$@; rename$was,$_ unless$was eq $_}' + -e syntax OK + $op = shift @ARGV || die("usage: $0 code [...]"); + chomp(@ARGV = <ARGV>) unless @ARGV; + foreach $_ (@ARGV) { + $was = $_; + eval $op; + die $@ if $@; + rename $was, $_ unless $was eq $_; + } + +The decompiler has several options for the code it generates. For +instance, you can set the size of each indent from 4 (as above) to +2 with: + + $ perl -MO=Deparse,-si2 myperlprogram + +The B<-p> option adds parentheses where normally they are omitted: + + $ perl -MO=Deparse -e 'print "Hello, world\n"' + -e syntax OK + print "Hello, world\n"; + $ perl -MO=Deparse,-p -e 'print "Hello, world\n"' + -e syntax OK + print("Hello, world\n"); + +See L<B::Deparse> for more information on the formatting options. + +=head2 The Lint Back End + +The lint back end (B::Lint) inspects programs for poor style. One +programmer's bad style is another programmer's useful tool, so options +let you select what is complained about. + +To run the style checker across your source code: + + $ perl -MO=Lint myperlprogram + +To disable context checks and undefined subroutines: + + $ perl -MO=Lint,-context,-undefined-subs myperlprogram + +See L<B::Lint> for information on the options. + +=head1 Module List for the Compiler Suite + +=over 4 + +=item B + +This module is the introspective ("reflective" in Java terms) +module, which allows a Perl program to inspect its innards. The +back end modules all use this module to gain access to the compiled +parse tree. You, the user of a back end module, will not need to +interact with B. + +=item O + +This module is the front-end to the compiler's back ends. Normally +called something like this: + + $ perl -MO=Deparse myperlprogram + +This is like saying C<use O 'Deparse'> in your Perl program. + +=item B::Concise + +This module prints a concise (but complete) version of the Perl parse +tree. Its output is more customizable than the one of B::Terse or +B::Debug (and it can emulate them). This module useful for people who +are writing their own back end, or who are learning about the Perl +internals. It's not useful to the average programmer. + +=item B::Debug + +This module dumps the Perl parse tree in verbose detail to STDOUT. +It's useful for people who are writing their own back end, or who +are learning about the Perl internals. It's not useful to the +average programmer. + +=item B::Deparse + +This module produces Perl source code from the compiled parse tree. +It is useful in debugging and deconstructing other people's code, +also as a pretty-printer for your own source. See +L</"The Decompiling Back End"> for details about usage. + +=item B::Lint + +This module inspects the compiled form of your source code for things +which, while some people frown on them, aren't necessarily bad enough +to justify a warning. For instance, use of an array in scalar context +without explicitly saying C<scalar(@array)> is something that Lint +can identify. See L</"The Lint Back End"> for details about usage. + +=item B::Showlex + +This module prints out the my() variables used in a function or a +file. To get a list of the my() variables used in the subroutine +mysub() defined in the file myperlprogram: + + $ perl -MO=Showlex,mysub myperlprogram + +To get a list of the my() variables used in the file myperlprogram: + + $ perl -MO=Showlex myperlprogram + +[BROKEN] + +=item B::Terse + +This module prints the contents of the parse tree, but without as much +information as B::Debug. For comparison, C<print "Hello, world."> +produced 96 lines of output from B::Debug, but only 6 from B::Terse. + +This module is useful for people who are writing their own back end, +or who are learning about the Perl internals. It's not useful to the +average programmer. + +=item B::Xref + +This module prints a report on where the variables, subroutines, and +formats are defined and used within a program and the modules it +loads. See L</"The Cross Referencing Back End"> for details about +usage. + +=back + +=head1 KNOWN PROBLEMS + +BEGIN{} blocks are executed while compiling your code. Any external +state that is initialized in BEGIN{}, such as opening files, initiating +database connections etc., do not behave properly. To work around +this, Perl has an INIT{} block that corresponds to code being executed +before your program begins running but after your program has finished +being compiled. Execution order: BEGIN{}, (possible save of state +through compiler back-end), INIT{}, program runs, END{}. + +=head1 AUTHOR + +This document was originally written by Nathan Torkington, and is now +maintained by the perl5-porters mailing list +I<perl5-porters@perl.org>. + +=cut |