regexp.html

Shall高级编程

></LI
><LI
><P
><A
NAME="QUEXREGEX"
></A
></P
><P
>The question mark -- <SPAN
CLASS="TOKEN"
>?</SPAN
> -- matches zero or
	      one of the previous RE. It is generally used for matching
	      single characters.</P
></LI
><LI
><P
><A
NAME="PLUSREF"
></A
></P
><P
>The plus -- <SPAN
CLASS="TOKEN"
>+</SPAN
> -- matches one or more of the
	    previous RE. It serves a role similar to the <SPAN
CLASS="TOKEN"
>*</SPAN
>, but
	    does <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> match zero occurrences.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;# GNU versions of sed and awk can use "+",
   2&nbsp;# but it needs to be escaped.
   3&nbsp;
   4&nbsp;echo a111b | sed -ne '/a1\+b/p'
   5&nbsp;echo a111b | grep 'a1\+b'
   6&nbsp;echo a111b | gawk '/a1+b/'
   7&nbsp;# All of above are equivalent.
   8&nbsp;
   9&nbsp;# Thanks, S.C.</PRE
></TD
></TR
></TABLE
></P
><P
><A
NAME="ESCPCB"
></A
></P
></LI
><LI
><P
><A
HREF="escapingsection.html#ESCP"
>Escaped</A
> <SPAN
CLASS="QUOTE"
>"curly
	      brackets"</SPAN
> -- <SPAN
CLASS="TOKEN"
>\{ \}</SPAN
> -- indicate the number
	      of occurrences of a preceding RE to match.</P
><P
>It is necessary to escape the curly brackets since
	      they have only their literal character meaning
	      otherwise. This usage is technically not part of the basic
	      RE set.</P
><P
><SPAN
CLASS="QUOTE"
>"[0-9]\{5\}"</SPAN
> matches exactly five digits
	      (characters in the range of 0 to 9).</P
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/note.png"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Curly brackets are not available as an RE in the
	      <SPAN
CLASS="QUOTE"
>"classic"</SPAN
> (non-POSIX compliant) version
	      of <A
HREF="awk.html#AWKREF"
>awk</A
>. However,
	      <B
CLASS="COMMAND"
>gawk</B
> has the
	      <TT
CLASS="OPTION"
>--re-interval</TT
> option that permits them
	      (without being escaped).</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo 2222 | gawk --re-interval '/2{3}/'</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>2222</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
><B
CLASS="COMMAND"
>Perl</B
> and some
	      <B
CLASS="COMMAND"
>egrep</B
> versions do not require escaping
	      the curly brackets.</P
></TD
></TR
></TABLE
></DIV
></LI
><LI
><P
><A
NAME="PARENGRPS"
></A
></P
><P
>Parentheses -- <B
CLASS="COMMAND"
>( )</B
> -- enclose a group of
	      REs. They are useful with the following
	      <SPAN
CLASS="QUOTE"
>"<SPAN
CLASS="TOKEN"
>|</SPAN
>"</SPAN
> operator and in <A
HREF="string-manipulation.html#EXPRPAREN"
>substring extraction</A
> using <A
HREF="moreadv.html#EXPRREF"
>expr</A
>.</P
></LI
><LI
><P
>The -- <B
CLASS="COMMAND"
>|</B
> -- <SPAN
CLASS="QUOTE"
>"or"</SPAN
> RE operator
	      matches any of a set of alternate characters.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>egrep 're(a|e)d' misc.txt</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>People who read seem to be better informed than those who do not.
 The clarinet produces sound by the vibration of its reed.</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	      </P
></LI
></UL
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/note.png"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Some versions of <B
CLASS="COMMAND"
>sed</B
>,
	      <B
CLASS="COMMAND"
>ed</B
>, and <B
CLASS="COMMAND"
>ex</B
> support
	      escaped versions of the extended Regular Expressions
	      described above, as do the GNU utilities.</P
></TD
></TR
></TABLE
></DIV
><UL
><LI
STYLE="list-style-type: square"
><DIV
CLASS="FORMALPARA"
><P
><B
><A
NAME="POSIXREF"
></A
>POSIX Character Classes. </B
><TT
CLASS="USERINPUT"
><B
>[:class:]</B
></TT
></P
></DIV
><P
>This is an alternate method of specifying a range of
	      characters to match.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:alnum:]</B
></TT
> matches alphabetic or
	      numeric characters. This is equivalent to
	      <TT
CLASS="USERINPUT"
><B
>A-Za-z0-9</B
></TT
>.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:alpha:]</B
></TT
> matches alphabetic
	      characters. This is equivalent to
	      <TT
CLASS="USERINPUT"
><B
>A-Za-z</B
></TT
>.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:blank:]</B
></TT
> matches a space or a
	      tab.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:cntrl:]</B
></TT
> matches control
	      characters.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:digit:]</B
></TT
> matches (decimal)
	      digits. This is equivalent to
	      <TT
CLASS="USERINPUT"
><B
>0-9</B
></TT
>.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:graph:]</B
></TT
> (graphic printable
	      characters). Matches characters in the range of ASCII 33 -
	      126. This is the same as <TT
CLASS="USERINPUT"
><B
>[:print:]</B
></TT
>,
	      below, but excluding the space character.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:lower:]</B
></TT
> matches lowercase
	      alphabetic characters. This is equivalent to
	      <TT
CLASS="USERINPUT"
><B
>a-z</B
></TT
>.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:print:]</B
></TT
> (printable
	      characters). Matches characters in the range of ASCII 32 -
	      126. This is the same as <TT
CLASS="USERINPUT"
><B
>[:graph:]</B
></TT
>,
	      above, but adding the space character.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:space:]</B
></TT
> matches whitespace
	      characters (space and horizontal tab).</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:upper:]</B
></TT
> matches uppercase
	      alphabetic characters. This is equivalent to
	      <TT
CLASS="USERINPUT"
><B
>A-Z</B
></TT
>.</P
></LI
><LI
><P
><TT
CLASS="USERINPUT"
><B
>[:xdigit:]</B
></TT
> matches hexadecimal
	      digits. This is equivalent to
	      <TT
CLASS="USERINPUT"
><B
>0-9A-Fa-f</B
></TT
>.</P
><DIV
CLASS="IMPORTANT"
><TABLE
CLASS="IMPORTANT"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/important.png"
HSPACE="5"
ALT="Important"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>POSIX character classes generally require quoting
	      or <A
HREF="tests.html#DBLBRACKETS"
>double brackets</A
>
	      ([[ ]]).</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>grep [[:digit:]] test.file</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>abc=723</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>These character classes may even be used with <A
HREF="globbingref.html"
>globbing</A
>, to a limited
	      extent.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>ls -l ?[[:digit:]][[:digit:]]?</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>-rw-rw-r--    1 bozo  bozo         0 Aug 21 14:47 a33b</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>To see POSIX character classes used in scripts, refer to
	      <A
HREF="textproc.html#EX49"
>Example 15-20</A
> and <A
HREF="textproc.html#LOWERCASE"
>Example 15-21</A
>.</P
></TD
></TR
></TABLE
></DIV
></LI
></UL
><P
><A
HREF="sedawk.html#SEDREF"
>Sed</A
>, <A
HREF="awk.html#AWKREF"
>awk</A
>, and <A
HREF="wrapper.html#PERLREF"
>Perl</A
>, used as filters in scripts, take
	  REs as arguments when "sifting" or transforming files or I/O
	  streams. See <A
HREF="contributed-scripts.html#BEHEAD"
>Example A-12</A
> and <A
HREF="contributed-scripts.html#TREE"
>Example A-17</A
>
	  for illustrations of this.</P
><P
>The standard reference on this complex topic is Friedl's
	  <I
CLASS="CITETITLE"
>Mastering Regular
	  Expressions</I
>. <I
CLASS="CITETITLE"
>Sed &#38;
	  Awk</I
>, by Dougherty and Robbins, also gives a very
	  lucid treatment of REs. See the <A
HREF="biblio.html"
><I
>Bibliography</I
></A
> for
	  more information on these books.</P
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN15785"
HREF="regexp.html#AEN15785"
>[1]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
><A
NAME="METAMEANINGREF"
></A
>A
	    <I
CLASS="FIRSTTERM"
>meta-meaning</I
> is the meaning of a
	    term or expression on a higher level of abstraction. For
	    example, the <I
CLASS="FIRSTTERM"
>literal</I
> meaning
	    of <I
CLASS="FIRSTTERM"
>regular expression</I
> is an
	    ordinary expression that conforms to accepted usage. The
	    <I
CLASS="FIRSTTERM"
>meta-meaning</I
> is drastically different,
	    as discussed at length in this chapter.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN15838"
HREF="regexp.html#AEN15838"
>[2]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Since <A
HREF="sedawk.html#SEDREF"
>sed</A
>, <A
HREF="awk.html#AWKREF"
>awk</A
>, and <A
HREF="textproc.html#GREPREF"
>grep</A
> process single lines, there
		  will usually not be a newline to match. In those cases where
		  there is a newline in a multiple line expression, the dot
		  will match the newline.
	            <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;sed -e 'N;s/.*/[&#38;]/' &#60;&#60; EOF   # Here Document
   4&nbsp;line1
   5&nbsp;line2
   6&nbsp;EOF
   7&nbsp;# OUTPUT:
   8&nbsp;# [line1
   9&nbsp;# line2]
  10&nbsp;
  11&nbsp;
  12&nbsp;
  13&nbsp;echo
  14&nbsp;
  15&nbsp;awk '{ $0=$1 "\n" $2; if (/line.1/) {print}}' &#60;&#60; EOF
  16&nbsp;line 1
  17&nbsp;line 2
  18&nbsp;EOF
  19&nbsp;# OUTPUT:
  20&nbsp;# line
  21&nbsp;# 1
  22&nbsp;
  23&nbsp;
  24&nbsp;# Thanks, S.C.
  25&nbsp;
  26&nbsp;exit 0</PRE
></TD
></TR
></TABLE
></P
></TD
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