1PERLCOMPILE(1) Perl Programmers Reference Guide PERLCOMPILE(1)
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6 perlcompile - Introduction to the Perl Compiler-Translator
7
9 Perl has always had a compiler: your source is compiled into an
10 internal form (a parse tree) which is then optimized before being run.
11 Since version 5.005, Perl has shipped with a module capable of
12 inspecting the optimized parse tree ("B"), and this has been used to
13 write many useful utilities, including a module that lets you turn your
14 Perl into C source code that can be compiled into a native executable.
15 The "B" module provides access to the parse tree, and other modules
17 ("back ends") do things with the tree. Some write it out as semi-
18 human-readable text. Another traverses the parse tree to build a
19 cross-reference of which subroutines, formats, and variables are used
20 where. Another checks your code for dubious constructs. Yet another
21 back end dumps the parse tree back out as Perl source, acting as a
22 source code beautifier or deobfuscator.
23 Because its original purpose was to be a way to produce C code
25 corresponding to a Perl program, and in turn a native executable, the
26 "B" module and its associated back ends are known as "the compiler",
27 even though they don't really compile anything. Different parts of the
28 compiler are more accurately a "translator", or an "inspector", but
29 people want Perl to have a "compiler option" not an "inspector gadget".
30 What can you do?
31 This document covers the use of the Perl compiler: which modules it
33 comprises, how to use the most important of the back end modules, what
34 problems there are, and how to work around them.
35 Layout
37 The compiler back ends are in the "B::" hierarchy, and the front-end
38 (the module that you, the user of the compiler, will sometimes interact
39 with) is the O module.
40 Here are the important back ends to know about, with their status
42 expressed as a number from 0 (outline for later implementation) to 10
43 (if there's a bug in it, we're very surprised):
44 B::Lint
46 Complains if it finds dubious constructs in your source code.
47 Status: 6 (it works adequately, but only has a very limited number
48 of areas that it checks).
49 B::Deparse
51 Recreates the Perl source, making an attempt to format it
52 coherently. Status: 8 (it works nicely, but a few obscure things
53 are missing).
54 B::Xref
56 Reports on the declaration and use of subroutines and variables.
57 Status: 8 (it works nicely, but still has a few lingering bugs).
58
60 The following sections describe how to use the various compiler back
61 ends. They're presented roughly in order of maturity, so that the most
62 stable and proven back ends are described first, and the most
63 experimental and incomplete back ends are described last.
64 The O module automatically enabled the -c flag to Perl, which prevents
66 Perl from executing your code once it has been compiled. This is why
67 all the back ends print:
68 myperlprogram syntax OK
70 before producing any other output.
72 The Cross Referencing Back End
74 The cross referencing back end (B::Xref) produces a report on your
75 program, breaking down declarations and uses of subroutines and
76 variables (and formats) by file and subroutine. For instance, here's
77 part of the report from the pod2man program that comes with Perl:
78 Subroutine clear_noremap
80 Package (lexical)
81 $ready_to_print i1069, 1079
82 Package main
83 $& 1086
84 $. 1086
85 $0 1086
86 $1 1087
87 $2 1085, 1085
88 $3 1085, 1085
89 $ARGV 1086
90 %HTML_Escapes 1085, 1085
91 This shows the variables used in the subroutine "clear_noremap". The
93 variable $ready_to_print is a my() (lexical) variable, introduced
94 (first declared with my()) on line 1069, and used on line 1079. The
95 variable $& from the main package is used on 1086, and so on.
96 A line number may be prefixed by a single letter:
98 i Lexical variable introduced (declared with my()) for the first
100 time.
101 & Subroutine or method call.
103 s Subroutine defined.
105 r Format defined.
107 The most useful option the cross referencer has is to save the report
109 to a separate file. For instance, to save the report on myperlprogram
110 to the file report:
111 $ perl -MO=Xref,-oreport myperlprogram
113 The Decompiling Back End
115 The Deparse back end turns your Perl source back into Perl source. It
116 can reformat along the way, making it useful as a deobfuscator. The
117 most basic way to use it is:
118 $ perl -MO=Deparse myperlprogram
120 You'll notice immediately that Perl has no idea of how to paragraph
122 your code. You'll have to separate chunks of code from each other with
123 newlines by hand. However, watch what it will do with one-liners:
124 $ perl -MO=Deparse -e '$op=shift||die "usage: $0
126 code [...]";chomp(@ARGV=<>)unless@ARGV; for(@ARGV){$was=$_;eval$op;
127 die$@ if$@; rename$was,$_ unless$was eq $_}'
128 -e syntax OK
129 $op = shift @ARGV || die("usage: $0 code [...]");
130 chomp(@ARGV = <ARGV>) unless @ARGV;
131 foreach $_ (@ARGV) {
132 $was = $_;
133 eval $op;
134 die $@ if $@;
135 rename $was, $_ unless $was eq $_;
136 }
137 The decompiler has several options for the code it generates. For
139 instance, you can set the size of each indent from 4 (as above) to 2
140 with:
141 $ perl -MO=Deparse,-si2 myperlprogram
143 The -p option adds parentheses where normally they are omitted:
145 $ perl -MO=Deparse -e 'print "Hello, world\n"'
147 -e syntax OK
148 print "Hello, world\n";
149 $ perl -MO=Deparse,-p -e 'print "Hello, world\n"'
150 -e syntax OK
151 print("Hello, world\n");
152 See B::Deparse for more information on the formatting options.
154 The Lint Back End
156 The lint back end (B::Lint) inspects programs for poor style. One
157 programmer's bad style is another programmer's useful tool, so options
158 let you select what is complained about.
159 To run the style checker across your source code:
161 $ perl -MO=Lint myperlprogram
163 To disable context checks and undefined subroutines:
165 $ perl -MO=Lint,-context,-undefined-subs myperlprogram
167 See B::Lint for information on the options.
169
171 B This module is the introspective ("reflective" in Java terms)
172 module, which allows a Perl program to inspect its innards. The
173 back end modules all use this module to gain access to the compiled
174 parse tree. You, the user of a back end module, will not need to
175 interact with B.
176 O This module is the front-end to the compiler's back ends. Normally
178 called something like this:
179 $ perl -MO=Deparse myperlprogram
181 This is like saying "use O 'Deparse'" in your Perl program.
183 B::Concise
185 This module prints a concise (but complete) version of the Perl
186 parse tree. Its output is more customizable than the one of
187 B::Terse or B::Debug (and it can emulate them). This module useful
188 for people who are writing their own back end, or who are learning
189 about the Perl internals. It's not useful to the average
190 programmer.
191 B::Debug
193 This module dumps the Perl parse tree in verbose detail to STDOUT.
194 It's useful for people who are writing their own back end, or who
195 are learning about the Perl internals. It's not useful to the
196 average programmer.
197 B::Deparse
199 This module produces Perl source code from the compiled parse tree.
200 It is useful in debugging and deconstructing other people's code,
201 also as a pretty-printer for your own source. See "The Decompiling
202 Back End" for details about usage.
203 B::Lint
205 This module inspects the compiled form of your source code for
206 things which, while some people frown on them, aren't necessarily
207 bad enough to justify a warning. For instance, use of an array in
208 scalar context without explicitly saying "scalar(@array)" is
209 something that Lint can identify. See "The Lint Back End" for
210 details about usage.
211 B::Showlex
213 This module prints out the my() variables used in a function or a
214 file. To get a list of the my() variables used in the subroutine
215 mysub() defined in the file myperlprogram:
216 $ perl -MO=Showlex,mysub myperlprogram
218 To get a list of the my() variables used in the file myperlprogram:
220 $ perl -MO=Showlex myperlprogram
222 [BROKEN]
224 B::Terse
226 This module prints the contents of the parse tree, but without as
227 much information as B::Debug. For comparison, "print "Hello,
228 world."" produced 96 lines of output from B::Debug, but only 6
229 from B::Terse.
230 This module is useful for people who are writing their own back
232 end, or who are learning about the Perl internals. It's not useful
233 to the average programmer.
234 B::Xref
236 This module prints a report on where the variables, subroutines,
237 and formats are defined and used within a program and the modules
238 it loads. See "The Cross Referencing Back End" for details about
239 usage.
240
242 BEGIN{} blocks are executed while compiling your code. Any external
243 state that is initialized in BEGIN{}, such as opening files, initiating
244 database connections etc., do not behave properly. To work around
245 this, Perl has an INIT{} block that corresponds to code being executed
246 before your program begins running but after your program has finished
247 being compiled. Execution order: BEGIN{}, (possible save of state
248 through compiler back-end), INIT{}, program runs, END{}.
249
251 This document was originally written by Nathan Torkington, and is now
252 maintained by the perl5-porters mailing list perl5-porters@perl.org.
253perl v5.10.1 2009-04-11 PERLCOMPILE(1)