18.6. Code Development ToolsThe O module has many interesting Modi Operandi beyond feeding the exasperatingly experimental code generators. By providing relatively painless access to the Perl compiler's output, this module makes it easy to build other tools that need to know everything about a Perl program. The B::Lint module is named after lint(1), the C program verifier. It inspects programs for questionable constructs that often trip up beginners but don't normally trigger warnings. Call the module directly: Only a few checks are currently defined, such as using an array in an implicit scalar context, relying on default variables, and accessing another package's (nominally private) identifiers that start with _. See B::Lint(3) for details.% perl -MO=Lint,all myprog The B::Xref module generates cross-reference listings of the declaration and use of all variables (both global and lexically scoped), subroutines, and formats in a program, broken down by file and subroutine. Call the module this way: For instance, here's a partial report:% perl -MO=Xref myprog > myprof.pxref This shows that the parse_argv subroutine had four lexical variables of its own; it also accessed global identifiers from both the main package and from Getopt::Long. The numbers are the lines where that item was used: a leading i indicates that the item was first introduced at the following line number, and a leading & means a subroutine was called there. Dereferences are listed separately, which is why both $Options and %$Options are shown.Subroutine parse_argv Package (lexical) $on i113, 114 $opt i113, 114 %getopt_cfg i107, 113 @cfg_args i112, 114, 116, 116 Package Getopt::Long $ignorecase 101 &GetOptions &124 Package main $Options 123, 124, 141, 150, 165, 169 %$Options 141, 150, 165, 169 &check_read &167 @ARGV 121, 157, 157, 162, 166, 166 The B::Deparse is a pretty printer that can demystify Perl code and help you understand what transformations the optimizer has taken with your code. For example, this shows what defaults Perl uses for various constructs: The -p switch adds parentheses so you can see Perl's idea of precedence:% perl -MO=Deparse -ne 'for (1 .. 10) { print if -t }' LINE: while (defined($_ = <ARGV>)) { foreach $_ (1 .. 10) { print $_ if -t STDIN; } } You can use -q to see what primitives interpolated strings are compiled into:% perl -MO=Deparse,-p -e 'print $a ** 3 + sqrt(2) / 10 ** -2 ** $c' print((($a ** 3) + (1.4142135623731 / (10 ** (-(2 ** $c)))))); And this shows how Perl really compiles a three-part for loop into a while loop:% perl -MO=Deparse,-q -e '"A $name and some @ARGV\n"' 'A ' . $name . ' and some ' . join($", @ARGV) . "\n"; You could even call B::Deparse on a Perl bytecode file produced by perlcc -b, and have it decompile that binary file for you. Serialized Perl opcodes may be a tad tough to read, but strong encryption they are not.% perl -MO=Deparse -e 'for ($i=0;$i<10;$i++) { $x++ }' $i = 0; while ($i < 10) { ++$x; } continue { ++$i } Copyright © 2001 O'Reilly & Associates. All rights reserved. |
|