00000002.htm

一份很好的linux入门资料

1&nbsp;<BR>
%&nbsp;set&nbsp;match&nbsp;<BR>
http&nbsp;<BR>
%&nbsp;regexp&nbsp;{^[^:]+(?=.*\.edu$)}&nbsp;$x&nbsp;match&nbsp;<BR>
0&nbsp;<BR>
%&nbsp;regexp&nbsp;{^[^:]*(?!.*\.edu$)}&nbsp;$x&nbsp;match&nbsp;<BR>
1&nbsp;<BR>
%&nbsp;set&nbsp;match&nbsp;<BR>
http&nbsp;<BR>
&nbsp;<BR>
The&nbsp;regular&nbsp;expressions&nbsp;above&nbsp;may&nbsp;seem&nbsp;complicated,&nbsp;but&nbsp;they're&nbsp;really&nbsp;&nbsp;<BR>
not&nbsp;bad!&nbsp;Find&nbsp;the&nbsp;lookahead&nbsp;expression&nbsp;in&nbsp;the&nbsp;first&nbsp;regexp&nbsp;command&nbsp;&nbsp;<BR>
above;&nbsp;it&nbsp;starts&nbsp;with&nbsp;(?=&nbsp;and&nbsp;ends&nbsp;at&nbsp;the&nbsp;corresponding&nbsp;parenthesis.&nbsp;The&nbsp;<BR>
&nbsp;&quot;guts&quot;&nbsp;of&nbsp;this&nbsp;lookahead&nbsp;expression&nbsp;is&nbsp;.*\.com$,&nbsp;which&nbsp;stands&nbsp;for&nbsp;&quot;a&nbsp;&nbsp;<BR>
string&nbsp;that&nbsp;ends&nbsp;with&nbsp;.com&quot;.&nbsp;So&nbsp;the&nbsp;first&nbsp;regexp&nbsp;command&nbsp;above&nbsp;matches&nbsp;&nbsp;<BR>
any&nbsp;string&nbsp;containing&nbsp;non-colon&nbsp;(:)&nbsp;characters,&nbsp;as&nbsp;long&nbsp;as&nbsp;the&nbsp;rest&nbsp;of&nbsp;&nbsp;<BR>
the&nbsp;string&nbsp;ends&nbsp;with&nbsp;.com.&nbsp;The&nbsp;second&nbsp;regexp&nbsp;is&nbsp;similar&nbsp;but&nbsp;looks&nbsp;for&nbsp;&nbsp;<BR>
a&nbsp;string&nbsp;ending&nbsp;with&nbsp;.edu.&nbsp;Because&nbsp;regexp&nbsp;returns&nbsp;0,&nbsp;you&nbsp;can&nbsp;see&nbsp;that&nbsp;&nbsp;<BR>
this&nbsp;doesn't&nbsp;match.&nbsp;The&nbsp;third&nbsp;regexp&nbsp;looks&nbsp;for&nbsp;a&nbsp;string&nbsp;not&nbsp;ending&nbsp;&nbsp;<BR>
with&nbsp;.edu.&nbsp;It&nbsp;matches&nbsp;because&nbsp;$x&nbsp;ends&nbsp;with&nbsp;.com.&nbsp;&nbsp;<BR>
Tcl&nbsp;8.1&nbsp;lets&nbsp;you&nbsp;document&nbsp;complex&nbsp;regular&nbsp;expressions&nbsp;by&nbsp;embedding&nbsp;&nbsp;<BR>
comments.&nbsp;See&nbsp;the&nbsp;next&nbsp;section.&nbsp;&nbsp;<BR>
&nbsp;<BR>
Switches&nbsp;<BR>
Tcl&nbsp;8.1&nbsp;added&nbsp;command&nbsp;switches&nbsp;to&nbsp;regexp&nbsp;and&nbsp;regsub.&nbsp;For&nbsp;a&nbsp;complete&nbsp;&nbsp;<BR>
list,&nbsp;see&nbsp;the&nbsp;commands'&nbsp;reference&nbsp;pages.&nbsp;Let's&nbsp;look&nbsp;at&nbsp;two&nbsp;of&nbsp;the&nbsp;most&nbsp;&nbsp;<BR>
important&nbsp;changes.&nbsp;&nbsp;<BR>
Complex&nbsp;REs&nbsp;can&nbsp;be&nbsp;difficult&nbsp;to&nbsp;document.&nbsp;The&nbsp;-expanded&nbsp;switch&nbsp;sets&nbsp;&nbsp;<BR>
expanded&nbsp;syntax,&nbsp;which&nbsp;lets&nbsp;you&nbsp;add&nbsp;comments&nbsp;within&nbsp;a&nbsp;regular&nbsp;&nbsp;<BR>
expression.&nbsp;Comments&nbsp;start&nbsp;with&nbsp;a&nbsp;#&nbsp;character;&nbsp;whitespace&nbsp;is&nbsp;ignored.&nbsp;&nbsp;<BR>
This&nbsp;is&nbsp;mostly&nbsp;for&nbsp;scripting&nbsp;--&nbsp;but&nbsp;you&nbsp;can&nbsp;also&nbsp;use&nbsp;it&nbsp;on&nbsp;a&nbsp;command&nbsp;&nbsp;<BR>
line,&nbsp;as&nbsp;we'll&nbsp;do&nbsp;in&nbsp;the&nbsp;example&nbsp;below.&nbsp;Let's&nbsp;look&nbsp;the&nbsp;same&nbsp;RE&nbsp;twice:&nbsp;&nbsp;<BR>
first&nbsp;in&nbsp;the&nbsp;standard&nbsp;compact&nbsp;syntax,&nbsp;and&nbsp;second&nbsp;in&nbsp;expanded&nbsp;syntax:&nbsp;&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
%&nbsp;set&nbsp;x&nbsp;<A HREF="http://www.ajubasolutions.com">http://www.ajubasolutions.com</A>&nbsp;<BR>
<A HREF="http://www.ajubasolutions.com">http://www.ajubasolutions.com</A>&nbsp;<BR>
%&nbsp;regexp&nbsp;{^[^:]+(?=.*\.com$)}&nbsp;$x&nbsp;match&nbsp;<BR>
1&nbsp;<BR>
%&nbsp;set&nbsp;match&nbsp;<BR>
http&nbsp;<BR>
%&nbsp;regexp&nbsp;-expanded&nbsp;{&nbsp;<BR>
&nbsp;&nbsp;^&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;beginning&nbsp;of&nbsp;string&nbsp;<BR>
&nbsp;&nbsp;[^:]+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;all&nbsp;characters&nbsp;to&nbsp;the&nbsp;first&nbsp;colon&nbsp;<BR>
&nbsp;&nbsp;(?=&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;begin&nbsp;positive&nbsp;lookahead&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;.*\.com$&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;for&nbsp;a&nbsp;trailing&nbsp;.com&nbsp;<BR>
&nbsp;&nbsp;)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;end&nbsp;positive&nbsp;lookahead&nbsp;<BR>
}&nbsp;$x&nbsp;match&nbsp;<BR>
1&nbsp;<BR>
%&nbsp;set&nbsp;match&nbsp;<BR>
http&nbsp;<BR>
&nbsp;<BR>
In&nbsp;expanded&nbsp;syntax,&nbsp;you&nbsp;can&nbsp;use&nbsp;space&nbsp;and&nbsp;tab&nbsp;characters&nbsp;to&nbsp;indent&nbsp;and&nbsp;&nbsp;<BR>
make&nbsp;your&nbsp;code&nbsp;clear.&nbsp;To&nbsp;enter&nbsp;actual&nbsp;space&nbsp;and&nbsp;tab&nbsp;characters&nbsp;into&nbsp;your&nbsp;<BR>
&nbsp;RE,&nbsp;use&nbsp;the&nbsp;escapes&nbsp;\s&nbsp;and&nbsp;\t,&nbsp;respectively.&nbsp;&nbsp;<BR>
The&nbsp;other&nbsp;important&nbsp;new&nbsp;switch&nbsp;we'll&nbsp;cover&nbsp;here&nbsp;is&nbsp;-line.&nbsp;It&nbsp;enables&nbsp;&nbsp;<BR>
newline-sensitive&nbsp;matching.&nbsp;By&nbsp;default&nbsp;(without&nbsp;-line),&nbsp;Tcl&nbsp;regular&nbsp;&nbsp;<BR>
expressions&nbsp;have&nbsp;always&nbsp;treated&nbsp;newlines&nbsp;as&nbsp;an&nbsp;ordinary&nbsp;character.&nbsp;For&nbsp;&nbsp;<BR>
example,&nbsp;if&nbsp;a&nbsp;string&nbsp;contains&nbsp;several&nbsp;lines&nbsp;(separated&nbsp;by&nbsp;newline&nbsp;&nbsp;<BR>
characters),&nbsp;the&nbsp;end-of-string&nbsp;anchor&nbsp;$&nbsp;wouldn't&nbsp;match&nbsp;at&nbsp;any&nbsp;of&nbsp;the&nbsp;&nbsp;<BR>
embedded&nbsp;newlines.&nbsp;To&nbsp;write&nbsp;code&nbsp;that&nbsp;matched&nbsp;line-by-line,&nbsp;you&nbsp;had&nbsp;to&nbsp;&nbsp;<BR>
read&nbsp;input&nbsp;lines&nbsp;one&nbsp;by&nbsp;one&nbsp;and&nbsp;do&nbsp;separate&nbsp;matches&nbsp;against&nbsp;each&nbsp;line.&nbsp;&nbsp;<BR>
&nbsp;<BR>
With&nbsp;the&nbsp;-line&nbsp;switch,&nbsp;the&nbsp;metacharacters&nbsp;^,&nbsp;$,&nbsp;.,&nbsp;and&nbsp;[]&nbsp;treat&nbsp;a&nbsp;&nbsp;<BR>
newline&nbsp;as&nbsp;the&nbsp;end&nbsp;of&nbsp;a&nbsp;&quot;line.&quot;&nbsp;So,&nbsp;for&nbsp;example,&nbsp;the&nbsp;regular&nbsp;&nbsp;<BR>
expression&nbsp;^San&nbsp;Jose&nbsp;matches&nbsp;the&nbsp;second&nbsp;line&nbsp;of&nbsp;input&nbsp;below:&nbsp;&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
%&nbsp;set&nbsp;x&nbsp;{Dolores&nbsp;Sanchez&nbsp;<BR>
San&nbsp;Jose,&nbsp;CA}&nbsp;<BR>
Dolores&nbsp;Sanchez&nbsp;<BR>
San&nbsp;Jose,&nbsp;CA&nbsp;<BR>
%&nbsp;regexp&nbsp;{^San&nbsp;Jose}&nbsp;$x&nbsp;match&nbsp;<BR>
0&nbsp;<BR>
%&nbsp;regexp&nbsp;-line&nbsp;{^San&nbsp;Jose}&nbsp;$x&nbsp;match&nbsp;<BR>
1&nbsp;<BR>
%&nbsp;set&nbsp;match&nbsp;<BR>
San&nbsp;Jose&nbsp;<BR>
&nbsp;<BR>
The&nbsp;-line&nbsp;switch&nbsp;actually&nbsp;enables&nbsp;two&nbsp;other&nbsp;switches.&nbsp;You&nbsp;can&nbsp;set&nbsp;part&nbsp;&nbsp;<BR>
of&nbsp;the&nbsp;features&nbsp;from&nbsp;-line&nbsp;by&nbsp;choosing&nbsp;one&nbsp;of&nbsp;these&nbsp;switches&nbsp;instead:&nbsp;&nbsp;<BR>
The&nbsp;-lineanchor&nbsp;switch&nbsp;makes&nbsp;^&nbsp;and&nbsp;$&nbsp;match&nbsp;at&nbsp;the&nbsp;beginning&nbsp;and&nbsp;end&nbsp;of&nbsp;a&nbsp;<BR>
&nbsp;line.&nbsp;The&nbsp;-linestop&nbsp;switch&nbsp;makes&nbsp;.&nbsp;and&nbsp;[]&nbsp;stop&nbsp;matching&nbsp;at&nbsp;a&nbsp;newline&nbsp;&nbsp;<BR>
character.&nbsp;&nbsp;<BR>
Options,&nbsp;Directors&nbsp;<BR>
This&nbsp;section&nbsp;introduces&nbsp;two&nbsp;more&nbsp;features&nbsp;from&nbsp;Tcl&nbsp;8.1.&nbsp;Details&nbsp;are&nbsp;in&nbsp;&nbsp;<BR>
the&nbsp;re_syntax(n)&nbsp;reference&nbsp;page.&nbsp;&nbsp;<BR>
An&nbsp;8.1&nbsp;RE&nbsp;can&nbsp;start&nbsp;with&nbsp;embedded&nbsp;options.&nbsp;These&nbsp;look&nbsp;like&nbsp;(?xyz),&nbsp;where&nbsp;<BR>
&nbsp;xyz&nbsp;are&nbsp;one&nbsp;or&nbsp;more&nbsp;option&nbsp;letters.&nbsp;For&nbsp;instance,&nbsp;(?i)ouch&nbsp;matches&nbsp;OUCH&nbsp;<BR>
&nbsp;because&nbsp;i&nbsp;is&nbsp;the&nbsp;&quot;case-insensitive&nbsp;matching&quot;&nbsp;option.&nbsp;Other&nbsp;options&nbsp;&nbsp;<BR>
include&nbsp;(?e),&nbsp;which&nbsp;marks&nbsp;the&nbsp;rest&nbsp;of&nbsp;the&nbsp;regular&nbsp;expression&nbsp;as&nbsp;an&nbsp;8.&nbsp;<BR>
0-style&nbsp;RE&nbsp;--&nbsp;to&nbsp;let&nbsp;you&nbsp;avoid&nbsp;confusion&nbsp;with&nbsp;the&nbsp;new&nbsp;8.1&nbsp;syntax.&nbsp;&nbsp;<BR>
&nbsp;<BR>
An&nbsp;RE&nbsp;can&nbsp;also&nbsp;start&nbsp;with&nbsp;three&nbsp;asterisks,&nbsp;which&nbsp;is&nbsp;a&nbsp;director.&nbsp;For&nbsp;&nbsp;<BR>
example,&nbsp;***=&nbsp;is&nbsp;the&nbsp;director&nbsp;that&nbsp;says&nbsp;the&nbsp;rest&nbsp;of&nbsp;the&nbsp;regular&nbsp;&nbsp;<BR>
expression&nbsp;is&nbsp;literal&nbsp;text.&nbsp;So&nbsp;the&nbsp;RE&nbsp;***=(?i)ouch&nbsp;matches&nbsp;exactly&nbsp;&nbsp;<BR>
(?i)ouch;&nbsp;the&nbsp;(?i)&nbsp;isn't&nbsp;treated&nbsp;as&nbsp;an&nbsp;option.&nbsp;&nbsp;<BR>
&nbsp;<BR>
Part&nbsp;3.&nbsp;Summary:&nbsp;Regular&nbsp;Expression&nbsp;Changes&nbsp;in&nbsp;Tcl&nbsp;8.1&nbsp;<BR>
Tcl&nbsp;8.1&nbsp;added&nbsp;advanced&nbsp;regular&nbsp;expression&nbsp;syntax.&nbsp;The&nbsp;new&nbsp;re_syntax(n)&nbsp;&nbsp;<BR>
reference&nbsp;page&nbsp;has&nbsp;details.&nbsp;&nbsp;<BR>
This&nbsp;table&nbsp;below&nbsp;summarizes&nbsp;the&nbsp;new&nbsp;syntax:&nbsp;{m}&nbsp;Matches&nbsp;m&nbsp;instances&nbsp;of&nbsp;&nbsp;<BR>
the&nbsp;previous&nbsp;pattern&nbsp;item&nbsp;&nbsp;<BR>
{m}?&nbsp;Matches&nbsp;m&nbsp;instances&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;Non-greedy.&nbsp;&nbsp;<BR>
{m,}&nbsp;Matches&nbsp;m&nbsp;or&nbsp;more&nbsp;instances&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;&nbsp;<BR>
{m,}?&nbsp;Matches&nbsp;m&nbsp;or&nbsp;more&nbsp;instances&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;&nbsp;<BR>
Non-greedy.&nbsp;&nbsp;<BR>
{m,n}&nbsp;Matches&nbsp;m&nbsp;through&nbsp;n&nbsp;instances&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;&nbsp;<BR>
{m,n}?&nbsp;Matches&nbsp;m&nbsp;through&nbsp;n&nbsp;instances&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;&nbsp;<BR>
Non-greedy.&nbsp;&nbsp;<BR>
*?&nbsp;Matches&nbsp;zero&nbsp;or&nbsp;more&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;Non-greedy.&nbsp;&nbsp;<BR>
+?&nbsp;Matches&nbsp;one&nbsp;or&nbsp;more&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;Non-greedy.&nbsp;&nbsp;<BR>
??&nbsp;Matches&nbsp;zero&nbsp;or&nbsp;one&nbsp;of&nbsp;the&nbsp;previous&nbsp;pattern&nbsp;item.&nbsp;Non-greedy.&nbsp;&nbsp;<BR>
(?:re)&nbsp;Groups&nbsp;a&nbsp;subpattern,&nbsp;re,&nbsp;but&nbsp;does&nbsp;not&nbsp;capture&nbsp;the&nbsp;result.&nbsp;&nbsp;<BR>
(?=re)&nbsp;Positive&nbsp;lookahead.&nbsp;Matches&nbsp;the&nbsp;point&nbsp;where&nbsp;re&nbsp;begins.&nbsp;&nbsp;<BR>
(?!re)&nbsp;Negative&nbsp;lookahead.&nbsp;Matches&nbsp;any&nbsp;point&nbsp;where&nbsp;re&nbsp;does&nbsp;not&nbsp;begin.&nbsp;&nbsp;<BR>
\c&nbsp;One&nbsp;of&nbsp;many&nbsp;backslash&nbsp;escapes.&nbsp;&nbsp;<BR>
[.&nbsp;.]&nbsp;Delimits&nbsp;a&nbsp;collating&nbsp;element&nbsp;within&nbsp;a&nbsp;bracketed&nbsp;expression.&nbsp;&nbsp;<BR>
[=&nbsp;=]&nbsp;Delimits&nbsp;an&nbsp;equivalence&nbsp;class&nbsp;within&nbsp;a&nbsp;bracketed&nbsp;expression.&nbsp;&nbsp;<BR>
[:&nbsp;:]&nbsp;Delimits&nbsp;a&nbsp;character&nbsp;class&nbsp;within&nbsp;a&nbsp;bracketed&nbsp;expression.&nbsp;&nbsp;<BR>
(?abc)&nbsp;Embedded&nbsp;options&nbsp;a,&nbsp;b,&nbsp;and&nbsp;c&nbsp;&nbsp;<BR>
***&nbsp;Director&nbsp;&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Some&nbsp;of&nbsp;the&nbsp;new&nbsp;switches&nbsp;for&nbsp;regexp&nbsp;and&nbsp;regsub&nbsp;are:&nbsp;-expanded&nbsp;Enable&nbsp;&nbsp;<BR>
expanded&nbsp;syntax&nbsp;(for&nbsp;comments)&nbsp;&nbsp;<BR>
-line&nbsp;Enable&nbsp;newline-sensitive&nbsp;matching&nbsp;&nbsp;<BR>
-linestop&nbsp;Make&nbsp;[]&nbsp;and&nbsp;.&nbsp;stop&nbsp;at&nbsp;newlines.&nbsp;&nbsp;<BR>
-lineanchor&nbsp;Make&nbsp;^&nbsp;and&nbsp;$&nbsp;match&nbsp;the&nbsp;start&nbsp;and&nbsp;end&nbsp;of&nbsp;a&nbsp;line.&nbsp;&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
--&nbsp;<BR>
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&nbsp;<BR>
&nbsp;<BR>
※&nbsp;来源:·BBS&nbsp;水木清华站&nbsp;smth.org·[FROM:&nbsp;202.204.7.234]&nbsp;<BR>


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