13－grep.mht

这是著名的源码浏览工具（不仅仅浏览

  <TBODY>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellHeading><A name=3DpgfId-998449></A>Symbol</P></TD>
    <TD>
      <P class=3DCellHeading><A =
name=3DpgfId-998451></A>Description</P></TD>
    <TD>
      <P class=3DCellHeading><A =
name=3DpgfId-998453></A>Example</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998455></A><SPAN =
class=3DBold>*</SPAN>=20
      (asterisk)</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998457></A>post-fix operator =
that matches=20
      an expression 0 or more times</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998459></A><SPAN=20
      class=3DBold>fo*<BR></SPAN>matches a string starting with <SPAN=20
      class=3DBold>f</SPAN> and ending with a repeating <SPAN =
class=3DBold>o</SPAN>=20
      or no <SPAN class=3DBold>o</SPAN>'s (such as <SPAN =
class=3DBold>f</SPAN>,=20
      <SPAN class=3DBold>fo</SPAN>, <SPAN =
class=3DBold>foo</SPAN>)</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998461></A><SPAN =
class=3DBold>+</SPAN>=20
      (plus)</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998463></A>post-fix operator =
that matches=20
      an expression at least once</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998465></A><SPAN=20
      class=3DBold>f+o<BR></SPAN>matches a string starting with one or =
more <SPAN=20
      class=3DBold>f</SPAN>'s and ending with an <SPAN =
class=3DBold>o</SPAN> (such=20
      as <SPAN class=3DBold>fo</SPAN>, <SPAN class=3DBold>ffo</SPAN>, =
and <SPAN=20
      class=3DBold>fffo</SPAN>)</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998467></A><SPAN =
class=3DBold>?</SPAN>=20
      (question mark)</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998469></A>post-fix operator =
that must=20
      match an expression once or not at all</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998471></A><SPAN=20
      class=3DBold>f?o<BR></SPAN>matches <SPAN class=3DBold>fo</SPAN> or =
<SPAN=20
      class=3DBold>o</SPAN> </P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998473></A><SPAN =
class=3DBold>{n}</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998475></A>preceding item is =
matched=20
      exactly <EM class=3DEmphasis>n</EM> times</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998477></A><SPAN=20
      class=3DBold>fo{2}<BR></SPAN>matches <SPAN class=3DBold>foo</SPAN> =
</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998479></A><SPAN =
class=3DBold>{n,}</SPAN>=20
      </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998481></A>proceeding item is =
matched <EM=20
      class=3DEmphasis>n</EM> or more times</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998483></A><SPAN=20
      class=3DBold>fo{2,}<BR></SPAN>matches <SPAN =
class=3DBold>foo</SPAN> and <SPAN=20
      class=3DBold>fooo</SPAN> </P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998485></A><SPAN =
class=3DBold>{,m}</SPAN>=20
      </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998487></A>proceeding item is =
optional and=20
      is matched at most <EM class=3DEmphasis>m</EM> times</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998489></A><SPAN=20
      class=3DBold>fo{,3}<BR></SPAN>matches <SPAN class=3DBold>f</SPAN>, =
<SPAN=20
      class=3DBold>fo</SPAN>, <SPAN class=3DBold>foo</SPAN>, and <SPAN=20
      class=3DBold>fooo</SPAN> </P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998491></A><SPAN =
class=3DBold>{n,m}</SPAN>=20
      </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998493></A>proceeding item is =
matched at=20
      least <EM class=3DEmphasis>n</EM> times and at most <EM=20
      class=3DEmphasis>m</EM> times</P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998495></A><SPAN=20
      class=3DBold>fo{1,3}<BR></SPAN>matches <SPAN =
class=3DBold>fo</SPAN>, <SPAN=20
      class=3DBold>foo</SPAN>, and <SPAN class=3DBold>fooo</SPAN>=20
</P></TD></TR></TBODY></TABLE>
<H3 class=3DHeading2><A name=3DpgfId-998496></A>Escape Sequences</H3>
<P class=3DBody><A name=3DpgfId-998497></A>Some characters cannot be =
included=20
literally in regular expressions. You represent them instead with escape =

sequences, which are characters beginning with a backslash (<SPAN=20
class=3DBold>\</SPAN>). A backslash is also part of the representation =
of=20
unprintable characters such as a tab or newline.</P>
<TABLE border=3D1>
  <CAPTION>
  <P class=3DTableTitle><A name=3DpgfId-998500></A>Escape =
Sequences</P></CAPTION>
  <TBODY>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellHeading><A name=3DpgfId-998504></A>Symbol</P></TD>
    <TD>
      <P class=3DCellHeading><A =
name=3DpgfId-998506></A>Description</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998508></A><SPAN =
class=3DBold>\\</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998510></A>a literal =
backslash</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998512></A><SPAN =
class=3DBold>\a</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998514></A>alert</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998516></A><SPAN =
class=3DBold>\f</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A =
name=3DpgfId-998518></A>formfeed</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998520></A><SPAN =
class=3DBold>\n</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A =
name=3DpgfId-998522></A>newline</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998524></A><SPAN =
class=3DBold>\r</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A =
name=3DpgfId-998526></A>return</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998528></A><SPAN =
class=3DBold>\t</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998530></A>horizontal =
tab</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998532></A><SPAN =
class=3DBold>\v</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998534></A>vertical =
tab</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998536></A><SPAN =
class=3DBold>\?</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998538></A>question =
mark</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998540></A><SPAN =
class=3DBold>\(</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998542></A>left =
parenthesis</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998544></A><SPAN =
class=3DBold>\)</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998546></A>right =
parenthesis</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998548></A><SPAN =
class=3DBold>\[</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998550></A>left =
bracket</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998552></A><SPAN =
class=3DBold>\]</SPAN>=20
    </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-998554></A>right=20
bracket</P></TD></TR></TBODY></TABLE>
<P class=3DBody><A name=3DpgfId-1001731></A>Two regular expressions may =
be=20
concatenated; the resulting regular expression matches any string formed =
by=20
concatenating two substrings that respectively match the concatenated=20
subexpression. For example:</P>
<TABLE>
  <TBODY>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-1001734></A><SPAN =
class=3DBold>[a-b]</SPAN>=20
      </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-1001736></A>matches either =
<SPAN=20
      class=3DBold>a</SPAN> or <SPAN class=3DBold>b</SPAN> =
</P></TD></TR>
  <TR vAlign=3Dtop>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-1001738></A><SPAN =
class=3DBold>[d-e]</SPAN>=20
      </P></TD>
    <TD>
      <P class=3DCellBody><A name=3DpgfId-1001740></A>matches either =
<SPAN=20
      class=3DBold>d</SPAN> or <SPAN class=3DBold>e</SPAN> =
</P></TD></TR>