b::deparse.3

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.\" ========================================================================
.\"
.IX Title "B::Deparse 3"
.TH B::Deparse 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
B::Deparse \- Perl compiler backend to produce perl code
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
\&\fBperl\fR \fB\-MO=Deparse\fR[\fB,\-d\fR][\fB,\-f\fR\fI\s-1FILE\s0\fR][\fB,\-p\fR][\fB,\-q\fR][\fB,\-l\fR]
        [\fB,\-s\fR\fI\s-1LETTERS\s0\fR][\fB,\-x\fR\fI\s-1LEVEL\s0\fR] \fIprog.pl\fR
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
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 \fB\-p\fR
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.
.PP
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 \s-1BUGS\s0 section below, you can help contribute to B::Deparse's
ongoing development by submitting a bug report with a small
example.
.SH "OPTIONS"
.IX Header "OPTIONS"
As with all compiler backend options, these must follow directly after
the '\-MO=Deparse', separated by a comma but not any white space.
.IP "\fB\-d\fR" 4
.IX Item "-d"
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).
.IP "\fB\-f\fR\fI\s-1FILE\s0\fR" 4
.IX Item "-fFILE"
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
\&\fB\-f\fR option with the filename. You can pass the \fB\-f\fR 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 \fB#line\fR directive with two parameters.
.IP "\fB\-l\fR" 4
.IX Item "-l"
Add '#line' declarations to the output based on the line and file
locations of the original code.
.IP "\fB\-p\fR" 4
.IX Item "-p"
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 \fB\-p\fR, it uses parentheses (almost)
whenever they would be legal. This can be useful if you are used to
\&\s-1LISP\s0, or if you want to see how perl parses your input. If you say
.Sp
.Vb 3
\&    if ($var & 0x7f == 65) {print "Gimme an A!"}
\&    print ($which ? $a : $b), "\en";
\&    $name = $ENV{USER} or "Bob";
.Ve
.Sp
\&\f(CW\*(C`B::Deparse,\-p\*(C'\fR will print
.Sp
.Vb 5
\&    if (($var & 0)) {
\&        print(\*(AqGimme an A!\*(Aq)
\&    };
\&    (print(($which ? $a : $b)), \*(Aq???\*(Aq);
\&    (($name = $ENV{\*(AqUSER\*(Aq}) or \*(Aq???\*(Aq)
.Ve
.Sp
which probably isn't what you intended (the \f(CW\*(Aq???\*(Aq\fR is a sign that
perl optimized away a constant value).
.IP "\fB\-P\fR" 4
.IX Item "-P"
Disable prototype checking. With this option, all function calls are
deparsed as if no prototype was defined for them. In other words,
.Sp
.Vb 1
\&    perl \-MO=Deparse,\-P \-e \*(Aqsub foo (\e@) { 1 } foo @x\*(Aq
.Ve
.Sp
will print
.Sp
.Vb 4
\&    sub foo (\e@) {
\&        1;
\&    }
\&    &foo(\e@x);
.Ve
.Sp
making clear how the parameters are actually passed to \f(CW\*(C`foo\*(C'\fR.
.IP "\fB\-q\fR" 4
.IX Item "-q"
Expand double-quoted strings into the corresponding combinations of
concatenation, uc, ucfirst, lc, lcfirst, quotemeta, and join. For
instance, print
.Sp
.Vb 1
\&    print "Hello, $world, @ladies, \eu$gentlemen\eE, \eu\eL$me!";
.Ve
.Sp
as
.Sp
.Vb 2
\&    print \*(AqHello, \*(Aq . $world . \*(Aq, \*(Aq . join($", @ladies) . \*(Aq, \*(Aq
\&          . ucfirst($gentlemen) . \*(Aq, \*(Aq . ucfirst(lc $me . \*(Aq!\*(Aq);
.Ve
.Sp
Note that the expanded form represents the way perl handles such
constructions internally \*(-- this option actually turns off the reverse
translation that B::Deparse usually does. On the other hand, note that
\&\f(CW\*(C`$x = "$y"\*(C'\fR is not the same as \f(CW\*(C`$x = $y\*(C'\fR: the former makes the value
of \f(CW$y\fR into a string before doing the assignment.
.IP "\fB\-s\fR\fI\s-1LETTERS\s0\fR" 4
.IX Item "-sLETTERS"
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:
.RS 4
.IP "\fBC\fR" 4
.IX Item "C"
Cuddle \f(CW\*(C`elsif\*(C'\fR, \f(CW\*(C`else\*(C'\fR, and \f(CW\*(C`continue\*(C'\fR blocks. For example, print
.Sp
.Vb 5
\&    if (...) {
\&         ...
\&    } else {
\&         ...
\&    }
.Ve
.Sp
instead of
.Sp
.Vb 6
\&    if (...) {
\&         ...
\&    }
\&    else {
\&         ...
\&    }
.Ve
.Sp
The default is not to cuddle.
.IP "\fBi\fR\fI\s-1NUMBER\s0\fR" 4
.IX Item "iNUMBER"
Indent lines by multiples of \fI\s-1NUMBER\s0\fR columns. The default is 4 columns.
.IP "\fBT\fR" 4
.IX Item "T"
Use tabs for each 8 columns of indent. The default is to use only spaces.
For instance, if the style options are \fB\-si4T\fR, a line that's indented
3 times will be preceded by one tab and four spaces; if the options were
\&\fB\-si8T\fR, the same line would be preceded by three tabs.
.IP "\fBv\fR\fI\s-1STRING\s0\fR\fB.\fR" 4
.IX Item "vSTRING."
Print \fI\s-1STRING\s0\fR for the value of a constant that can't be determined
because it was optimized away (mnemonic: this happens when a constant
is used in \fBv\fRoid context). The end of the string is marked by a period.
The string should be a valid perl expression, generally a constant.
Note that unless it's a number, it probably needs to be quoted, and on
a command line quotes need to be protected from the shell. Some
conventional values include 0, 1, 42, '', 'foo', and
\&'Useless use of constant omitted' (which may need to be
\&\fB\-sv\*(L"'Useless use of constant omitted'.\*(R"\fR
or something similar depending on your shell). The default is '???'.