B::Deparse - Perl compiler backend to produce perl code
perl -MO=Deparse[,-d][,-fFILE][,-p][,-q][,-l] [,-sLETTERS][,-xLEVEL] prog.pl
B::Deparse is a backend module for the Perl compiler that generates perl source code, based on the internal compiled structure that perl itself creates after parsing a program. The output of B::Deparse won't be exactly the same as the original source, since perl doesn't keep track of comments or whitespace, and there isn't a one-to-one correspondence between perl's syntactical constructions and their compiled form, but it will often be close. When you use the -p option, the output also includes parentheses even when they are not required by precedence, which can make it easy to see if perl is parsing your expressions the way you intended.
While B::Deparse goes to some lengths to try to figure out what your original program was doing, some parts of the language can still trip it up; it still fails even on some parts of Perl's own test suite. If you encounter a failure other than the most common ones described in the BUGS section below, you can help contribute to B::Deparse's ongoing development by submitting a bug report with a small example.
As with all compiler backend options, these must follow directly after the '-MO=Deparse', separated by a comma but not any white space.
Output data values (when they appear as constants) using Data::Dumper. Without this option, B::Deparse will use some simple routines of its own for the same purpose. Currently, Data::Dumper is better for some kinds of data (such as complex structures with sharing and self-reference) while the built-in routines are better for others (such as odd floating-point values).
Normally, B::Deparse deparses the main code of a program, and all the subs defined in the same file. To include subs defined in other files, pass the -f option with the filename. You can pass the -f option several times, to include more than one secondary file. (Most of the time you don't want to use it at all.) You can also use this option to include subs which are defined in the scope of a #line directive with two parameters.
Add '#line' declarations to the output based on the line and file locations of the original code.
Print extra parentheses. Without this option, B::Deparse includes parentheses in its output only when they are needed, based on the structure of your program. With -p, it uses parentheses (almost) whenever they would be legal. This can be useful if you are used to LISP, or if you want to see how perl parses your input. If you say
if ($var & 0x7f == 65) {print "Gimme an A!"}
print ($which ? $a : $b), "\n";
$name = $ENV{USER} or "Bob";B::Deparse,-p will print
if (($var & 0)) {
print('Gimme an A!')
};
(print(($which ? $a : $b)), '???');
(($name = $ENV{'USER'}) or '???')which probably isn't what you intended (the '???' is a sign that perl optimized away a constant value).
Disable prototype checking. With this option, all function calls are deparsed as if no prototype was defined for them. In other words,
perl -MO=Deparse,-P -e 'sub foo (\@) { 1 } foo @x'will print
sub foo (\@) {
1;
}
&foo(\@x);making clear how the parameters are actually passed to foo.
Expand double-quoted strings into the corresponding combinations of concatenation, uc, ucfirst, lc, lcfirst, quotemeta, and join. For instance, print
print "Hello, $world, @ladies, \u$gentlemen\E, \u\L$me!";as
print 'Hello, ' . $world . ', ' . join($", @ladies) . ', '
. ucfirst($gentlemen) . ', ' . ucfirst(lc $me . '!');Note that the expanded form represents the way perl handles such constructions internally -- this option actually turns off the reverse translation that B::Deparse usually does. On the other hand, note that $x = "$y" is not the same as $x = $y: the former makes the value of $y into a string before doing the assignment.
Tweak the style of B::Deparse's output. The letters should follow directly after the 's', with no space or punctuation. The following options are available:
Cuddle elsif, else, and continue blocks. For example, print
if (...) {
...
} else {
...
}instead of
if (...) {
...
}
else {
...
}The default is not to cuddle.
Indent lines by multiples of NUMBER columns. The default is 4 columns.
Use tabs for each 8 columns of indent. The default is to use only spaces. For instance, if the style options are -si4T, a line that's indented 3 times will be preceded by one tab and four spaces; if the options were -si8T, the same line would be preceded by three tabs.