perlrebackslash.1

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.

.\" Automatically generated by Pod::Man 2.16 (Pod::Simple 3.05)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sh \" Subsection heading
.br
.if t .Sp
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  \*(C+ will
.\" give a nicer C++.  Capital omega is used to do unbreakable dashes and
.\" therefore won't be available.  \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.ie \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
..
.    nr % 0
.    rr F
.\}
.el \{\
.    de IX
..
.\}
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ========================================================================
.\"
.IX Title "PERLREBACKSLASH 1"
.TH PERLREBACKSLASH 1 "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"
perlrebackslash \- Perl Regular Expression Backslash Sequences and Escapes
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The top level documentation about Perl regular expressions
is found in perlre.
.PP
This document describes all backslash and escape sequences. After
explaining the role of the backslash, it lists all the sequences that have
a special meaning in Perl regular expressions (in alphabetical order),
then describes each of them.
.PP
Most sequences are described in detail in different documents; the primary
purpose of this document is to have a quick reference guide describing all
backslash and escape sequences.
.Sh "The backslash"
.IX Subsection "The backslash"
In a regular expression, the backslash can perform one of two tasks:
it either takes away the special meaning of the character following it
(for instance, \f(CW\*(C`\e|\*(C'\fR matches a vertical bar, it's not an alternation),
or it is the start of a backslash or escape sequence.
.PP
The rules determining what it is are quite simple: if the character
following the backslash is a punctuation (non-word) character (that is,
anything that is not a letter, digit or underscore), then the backslash
just takes away the special meaning (if any) of the character following
it.
.PP
If the character following the backslash is a letter or a digit, then the
sequence may be special; if so, it's listed below. A few letters have not
been used yet, and escaping them with a backslash is safe for now, but a
future version of Perl may assign a special meaning to it. However, if you
have warnings turned on, Perl will issue a warning if you use such a sequence.
[1].
.PP
It is however guaranteed that backslash or escape sequences never have a
punctuation character following the backslash, not now, and not in a future
version of Perl 5. So it is safe to put a backslash in front of a non-word
character.
.PP
Note that the backslash itself is special; if you want to match a backslash,
you have to escape the backslash with a backslash: \f(CW\*(C`/\e\e/\*(C'\fR matches a single
backslash.
.IP "[1]" 4
.IX Item "[1]"
There is one exception. If you use an alphanumerical character as the
delimiter of your pattern (which you probably shouldn't do for readability
reasons), you will have to escape the delimiter if you want to match
it. Perl won't warn then. See also \*(L"Gory details of parsing
quoted constructs\*(R" in perlop.
.Sh "All the sequences and escapes"
.IX Subsection "All the sequences and escapes"
.Vb 10
\& \e000              Octal escape sequence.
\& \e1                Absolute backreference.
\& \ea                Alarm or bell.
\& \eA                Beginning of string.
\& \eb                Word/non\-word boundary. (Backspace in a char class).
\& \eB                Not a word/non\-word boundary.
\& \ecX               Control\-X (X can be any ASCII character).
\& \eC                Single octet, even under UTF\-8.
\& \ed                Character class for digits.
\& \eD                Character class for non\-digits.
\& \ee                Escape character.
\& \eE                Turn off \eQ, \eL and \eU processing.
\& \ef                Form feed.
\& \eg{}, \eg1         Named, absolute or relative backreference.
\& \eG                Pos assertion.
\& \eh                Character class for horizontal white space.
\& \eH                Character class for non horizontal white space.
\& \ek{}, \ek<>, \ek\*(Aq\*(Aq  Named backreference.
\& \eK                Keep the stuff left of \eK.
\& \el                Lowercase next character.
\& \eL                Lowercase till \eE.
\& \en                (Logical) newline character.
\& \eN{}              Named (Unicode) character.
\& \ep{}, \epP         Character with a Unicode property.
\& \eP{}, \ePP         Character without a Unicode property.
\& \eQ                Quotemeta till \eE.
\& \er                Return character.
\& \eR                Generic new line.
\& \es                Character class for white space.
\& \eS                Character class for non white space.
\& \et                Tab character.
\& \eu                Titlecase next character.
\& \eU                Uppercase till \eE.
\& \ev                Character class for vertical white space.
\& \eV                Character class for non vertical white space.
\& \ew                Character class for word characters.
\& \eW                Character class for non\-word characters.
\& \ex{}, \ex00        Hexadecimal escape sequence.
\& \eX                Extended Unicode "combining character sequence".
\& \ez                End of string.
\& \eZ                End of string.
.Ve
.Sh "Character Escapes"
.IX Subsection "Character Escapes"
\fIFixed characters\fR
.IX Subsection "Fixed characters"
.PP
A handful of characters have a dedicated \fIcharacter escape\fR. The following
table shows them, along with their code points (in decimal and hex), their
\&\s-1ASCII\s0 name, the control escape (see below) and a short description.
.PP
.Vb 9
\& Seq.  Code Point  ASCII   Cntr    Description.
\&       Dec    Hex
\&  \ea     7     07    BEL    \ecG    alarm or bell
\&  \eb     8     08     BS    \ecH    backspace [1]
\&  \ee    27     1B    ESC    \ec[    escape character
\&  \ef    12     0C     FF    \ecL    form feed
\&  \en    10     0A     LF    \ecJ    line feed [2]
\&  \er    13     0D     CR    \ecM    carriage return
\&  \et     9     09    TAB    \ecI    tab
.Ve
.IP "[1]" 4
.IX Item "[1]"
\&\f(CW\*(C`\eb\*(C'\fR is only the backspace character inside a character class. Outside a
character class, \f(CW\*(C`\eb\*(C'\fR is a word/non\-word boundary.
.IP "[2]" 4
.IX Item "[2]"
\&\f(CW\*(C`\en\*(C'\fR matches a logical newline. Perl will convert between \f(CW\*(C`\en\*(C'\fR and your
OSses native newline character when reading from or writing to text files.
.PP
Example
.IX Subsection "Example"
.PP
.Vb 1
\& $str =~ /\et/;   # Matches if $str contains a (horizontal) tab.
.Ve
.PP
\fIControl characters\fR
.IX Subsection "Control characters"
.PP
\&\f(CW\*(C`\ec\*(C'\fR is used to denote a control character; the character following \f(CW\*(C`\ec\*(C'\fR
is the name of the control character. For instance, \f(CW\*(C`/\ecM/\*(C'\fR matches the
character \fIcontrol-M\fR (a carriage return, code point 13). The case of the
character following \f(CW\*(C`\ec\*(C'\fR doesn't matter: \f(CW\*(C`\ecM\*(C'\fR and \f(CW\*(C`\ecm\*(C'\fR match the same
character.
.PP
Mnemonic: \fIc\fRontrol character.
.PP
Example
.IX Subsection "Example"
.PP
.Vb 1
\& $str =~ /\ecK/;  # Matches if $str contains a vertical tab (control\-K).
.Ve
.PP
\fINamed characters\fR
.IX Subsection "Named characters"
.PP
All Unicode characters have a Unicode name, and characters in various scripts
have names as well. It is even possible to give your own names to characters.
You can use a character by name by using the \f(CW\*(C`\eN{}\*(C'\fR construct; the name of
the character goes between the curly braces. You do have to \f(CW\*(C`use charnames\*(C'\fR
to load the names of the characters, otherwise Perl will complain you use
a name it doesn't know about. For more details, see charnames.
.PP
Mnemonic: \fIN\fRamed character.
.PP
Example
.IX Subsection "Example"
.PP
.Vb 2
\& use charnames \*(Aq:full\*(Aq;               # Loads the Unicode names.
\& $str =~ /\eN{THAI CHARACTER SO SO}/;  # Matches the Thai SO SO character
\&
\& use charnames \*(AqCyrillic\*(Aq;            # Loads Cyrillic names.
\& $str =~ /\eN{ZHE}\eN{KA}/;             # Match "ZHE" followed by "KA".
.Ve
.PP
\fIOctal escapes\fR
.IX Subsection "Octal escapes"
.PP
Octal escapes consist of a backslash followed by two or three octal digits
matching the code point of the character you want to use. This allows for
512 characters (\f(CW\*(C`\e00\*(C'\fR up to \f(CW\*(C`\e777\*(C'\fR) that can be expressed this way.
Enough in pre-Unicode days, but most Unicode characters cannot be escaped
this way.
.PP
Note that a character that is expressed as an octal escape is considered
as a character without special meaning by the regex engine, and will match
\&\*(L"as is\*(R".
.PP
Examples
.IX Subsection "Examples"
.PP
.Vb 4
\& $str = "Perl";
\& $str =~ /\e120/;    # Match, "\e120" is "P".
\& $str =~ /\e120+/;   # Match, "\e120" is "P", it is repeated at least once.
\& $str =~ /P\e053/;   # No match, "\e053" is "+" and taken literally.
.Ve
.PP
Caveat
.IX Subsection "Caveat"