re.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

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.\" ========================================================================
.\"
.IX Title "re 3"
.TH re 3 "2008-01-23" "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"
re \- Perl pragma to alter regular expression behaviour
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    use re \*(Aqtaint\*(Aq;
\&    ($x) = ($^X =~ /^(.*)$/s);     # $x is tainted here
\&
\&    $pat = \*(Aq(?{ $foo = 1 })\*(Aq;
\&    use re \*(Aqeval\*(Aq;
\&    /foo${pat}bar/;                # won\*(Aqt fail (when not under \-T switch)
\&
\&    {
\&        no re \*(Aqtaint\*(Aq;             # the default
\&        ($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here
\&
\&        no re \*(Aqeval\*(Aq;              # the default
\&        /foo${pat}bar/;            # disallowed (with or without \-T switch)
\&    }
\&
\&    use re \*(Aqdebug\*(Aq;                # output debugging info during
\&    /^(.*)$/s;                     #     compile and run time
\&
\&
\&    use re \*(Aqdebugcolor\*(Aq;           # same as \*(Aqdebug\*(Aq, but with colored output
\&    ...
\&
\&    use re qw(Debug All);          # Finer tuned debugging options.
\&    use re qw(Debug More);
\&    no re qw(Debug ALL);           # Turn of all re debugging in this scope
\&
\&    use re qw(is_regexp regexp_pattern); # import utility functions
\&    my ($pat,$mods)=regexp_pattern(qr/foo/i);
\&    if (is_regexp($obj)) { 
\&        print "Got regexp: ",
\&            scalar regexp_pattern($obj); # just as perl would stringify it
\&    }                                    # but no hassle with blessed re\*(Aqs.
.Ve
.PP
(We use $^X in these examples because it's tainted by default.)
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
.Sh "'taint' mode"
.IX Subsection "'taint' mode"
When \f(CW\*(C`use re \*(Aqtaint\*(Aq\*(C'\fR is in effect, and a tainted string is the target
of a regex, the regex memories (or values returned by the m// operator
in list context) are tainted.  This feature is useful when regex operations
on tainted data aren't meant to extract safe substrings, but to perform
other transformations.
.Sh "'eval' mode"
.IX Subsection "'eval' mode"
When \f(CW\*(C`use re \*(Aqeval\*(Aq\*(C'\fR is in effect, a regex is allowed to contain
\&\f(CW\*(C`(?{ ... })\*(C'\fR zero-width assertions even if regular expression contains
variable interpolation.  That is normally disallowed, since it is a
potential security risk.  Note that this pragma is ignored when the regular
expression is obtained from tainted data, i.e.  evaluation is always
disallowed with tainted regular expressions.  See \*(L"(?{ code })\*(R" in perlre.
.PP
For the purpose of this pragma, interpolation of precompiled regular
expressions (i.e., the result of \f(CW\*(C`qr//\*(C'\fR) is \fInot\fR considered variable
interpolation.  Thus:
.PP
.Vb 1
\&    /foo${pat}bar/
.Ve
.PP
\&\fIis\fR allowed if \f(CW$pat\fR is a precompiled regular expression, even
if \f(CW$pat\fR contains \f(CW\*(C`(?{ ... })\*(C'\fR assertions.
.Sh "'debug' mode"
.IX Subsection "'debug' mode"
When \f(CW\*(C`use re \*(Aqdebug\*(Aq\*(C'\fR is in effect, perl emits debugging messages when
compiling and using regular expressions.  The output is the same as that
obtained by running a \f(CW\*(C`\-DDEBUGGING\*(C'\fR\-enabled perl interpreter with the
\&\fB\-Dr\fR switch. It may be quite voluminous depending on the complexity
of the match.  Using \f(CW\*(C`debugcolor\*(C'\fR instead of \f(CW\*(C`debug\*(C'\fR enables a
form of output that can be used to get a colorful display on terminals
that understand termcap color sequences.  Set \f(CW$ENV{PERL_RE_TC}\fR to a
comma-separated list of \f(CW\*(C`termcap\*(C'\fR properties to use for highlighting
strings on/off, pre-point part on/off.
See \*(L"Debugging regular expressions\*(R" in perldebug for additional info.
.PP
As of 5.9.5 the directive \f(CW\*(C`use re \*(Aqdebug\*(Aq\*(C'\fR and its equivalents are
lexically scoped, as the other directives are.  However they have both 
compile-time and run-time effects.
.PP
See \*(L"Pragmatic Modules\*(R" in perlmodlib.
.Sh "'Debug' mode"