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<TITLE>BBS水木清华站∶精华区</TITLE></HEAD><BODY><CENTER><H1>BBS水木清华站∶精华区</H1></CENTER>发信人:&nbsp;dfbb&nbsp;(赵无忌),&nbsp;信区:&nbsp;Linux&nbsp;<BR>标&nbsp;&nbsp;题:&nbsp;[doc]Programminl&nbsp;Perl&nbsp;Chap1&nbsp;<BR>发信站:&nbsp;BBS&nbsp;水木清华站&nbsp;(Fri&nbsp;May&nbsp;&nbsp;8&nbsp;22:06:33&nbsp;1998)&nbsp;<BR>&nbsp;<BR>&nbsp;&lt;!DOCTYPE&nbsp;HTML&nbsp;PUBLIC&nbsp;&quot;-//W3C//DTD&nbsp;HTML&nbsp;3.2//EN&quot;&gt;&nbsp;<BR>&nbsp;&lt;HTML&gt;&nbsp;<BR>&nbsp;&lt;HEAD&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;TITLE&gt;[Chapter&nbsp;1]&nbsp;An&nbsp;Overview&nbsp;of&nbsp;Perl[Chapter&nbsp;1]&nbsp;1.2&nbsp;Natural&nbsp;and&nbsp;Artificial&nbsp;Languages[Chapter&nbsp;1]&nbsp;1.3&nbsp;A&nbsp;Grade&nbsp;Example[Chapter&nbsp;1]&nbsp;1.4&nbsp;Filehandles[Chapter&nbsp;1]&nbsp;1.5&nbsp;Operators[Chapter&nbsp;1]&nbsp;1.6&nbsp;Control&nbsp;Structures[Chapter&nbsp;1]&nbsp;1.7&nbsp;Regular&nbsp;Expressions[Chapter&nbsp;1]&nbsp;&nbsp;<BR>1.8&nbsp;List&nbsp;Processing[Chapter&nbsp;1]&nbsp;1.9&nbsp;What&nbsp;You&nbsp;Don't&nbsp;Know&nbsp;Won't&nbsp;Hurt&nbsp;You&nbsp;(Much)&lt;/TITLE&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;author&quot;&nbsp;CONTENT=&quot;Larry&nbsp;Wall,&nbsp;Tom&nbsp;Christiansen,&nbsp;and&nbsp;Randal&nbsp;Schwartz&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;date&quot;&nbsp;CONTENT=&quot;Fri&nbsp;Aug&nbsp;29&nbsp;18:27:39&nbsp;1997&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;form&quot;&nbsp;CONTENT=&quot;html&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;metadata&quot;&nbsp;CONTENT=&quot;dublincore.0.1&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;objecttype&quot;&nbsp;CONTENT=&quot;book&nbsp;part&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;otheragent&quot;&nbsp;CONTENT=&quot;gmat&nbsp;dbtohtml&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;publisher&quot;&nbsp;CONTENT=&quot;O'Reilly&nbsp;&amp;&nbsp;Associates,&nbsp;Inc.&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;source&quot;&nbsp;CONTENT=&quot;SGML&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;subject&quot;&nbsp;CONTENT=&quot;Perl&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;title&quot;&nbsp;CONTENT=&quot;Programming&nbsp;Perl,&nbsp;Second&nbsp;Edition&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;HTTP-EQUIV=&quot;Content-Script-Type&quot;&nbsp;CONTENT=&quot;text/javascript&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;META&nbsp;NAME=&quot;GENERATOR&quot;&nbsp;CONTENT=&quot;Mozilla/3.01Gold&nbsp;(Win95;&nbsp;I)&nbsp;[Netscape]&quot;&gt;&nbsp;<BR>&nbsp;&lt;/HEAD&gt;&nbsp;<BR>&nbsp;&lt;BODY&nbsp;TEXT=&quot;#000000&quot;&nbsp;BGCOLOR=&quot;#FFFFFF&quot;&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;H1&gt;&lt;A&nbsp;NAME=&quot;PERL2-CH-1&quot;&gt;&lt;/A&gt;1.&nbsp;An&nbsp;Overview&nbsp;of&nbsp;Perl&lt;/H1&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;&lt;B&gt;Contents:&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/B&gt;Getting&nbsp;Started&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;A&nbsp;HREF=&quot;ch01_02.htm&quot;&gt;Natural&nbsp;and&nbsp;Artificial&nbsp;Languages&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/A&gt;&lt;A&nbsp;HREF=&quot;ch01_03.htm&quot;&gt;A&nbsp;Grade&nbsp;Example&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/A&gt;&lt;A&nbsp;HREF=&quot;ch01_04.htm&quot;&gt;Filehandles&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/A&gt;&lt;A&nbsp;HREF=&quot;ch01_05.htm&quot;&gt;Operators&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/A&gt;&lt;A&nbsp;HREF=&quot;ch01_06.htm&quot;&gt;Control&nbsp;Structures&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/A&gt;&lt;A&nbsp;HREF=&quot;ch01_07.htm&quot;&gt;Regular&nbsp;Expressions&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/A&gt;&lt;A&nbsp;HREF=&quot;ch01_08.htm&quot;&gt;List&nbsp;Processing&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/A&gt;&lt;A&nbsp;HREF=&quot;ch01_09.htm&quot;&gt;What&nbsp;You&nbsp;Don't&nbsp;Know&nbsp;Won't&nbsp;Hurt&nbsp;You&nbsp;(Much)&lt;/A&gt;&lt;BR&gt;&nbsp;<BR>&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;H2&gt;&lt;A&nbsp;NAME=&quot;PERL2-CH-1-SECT-1&quot;&gt;&lt;/A&gt;1.1&nbsp;Getting&nbsp;Started&lt;/H2&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;We&nbsp;think&nbsp;that&nbsp;Perl&nbsp;is&nbsp;an&nbsp;easy&nbsp;language&nbsp;to&nbsp;learn&nbsp;and&nbsp;use,&nbsp;and&nbsp;we&nbsp;hope&nbsp;<BR>&nbsp;to&nbsp;convince&nbsp;you&nbsp;that&nbsp;we're&nbsp;right.&nbsp;One&nbsp;thing&nbsp;that's&nbsp;easy&nbsp;about&nbsp;Perl&nbsp;is&nbsp;that&nbsp;<BR>&nbsp;you&nbsp;don't&nbsp;have&nbsp;to&nbsp;say&nbsp;much&nbsp;before&nbsp;you&nbsp;say&nbsp;what&nbsp;you&nbsp;want&nbsp;to&nbsp;say.&nbsp;In&nbsp;many&nbsp;<BR>&nbsp;programming&nbsp;languages,&nbsp;you&nbsp;have&nbsp;to&nbsp;declare&nbsp;the&nbsp;types,&nbsp;variables,&nbsp;and&nbsp;subroutines&nbsp;<BR>&nbsp;you&nbsp;are&nbsp;going&nbsp;to&nbsp;use&nbsp;before&nbsp;you&nbsp;can&nbsp;write&nbsp;the&nbsp;first&nbsp;statement&nbsp;of&nbsp;executable&nbsp;<BR>&nbsp;code.&nbsp;And&nbsp;for&nbsp;complex&nbsp;problems&nbsp;demanding&nbsp;complex&nbsp;data&nbsp;structures,&nbsp;this&nbsp;<BR>&nbsp;is&nbsp;a&nbsp;good&nbsp;idea.&nbsp;But&nbsp;for&nbsp;many&nbsp;simple,&nbsp;everyday&nbsp;problems,&nbsp;you&nbsp;would&nbsp;like&nbsp;<BR>&nbsp;a&nbsp;programming&nbsp;language&nbsp;in&nbsp;which&nbsp;you&nbsp;can&nbsp;simply&nbsp;say:&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;PRE&gt;print&nbsp;&amp;quot;Howdy,&nbsp;world!\n&amp;quot;;&nbsp;<BR>&nbsp;&lt;/PRE&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;and&nbsp;expect&nbsp;the&nbsp;program&nbsp;to&nbsp;do&nbsp;just&nbsp;that.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;Perl&nbsp;is&nbsp;such&nbsp;a&nbsp;language.&nbsp;In&nbsp;fact,&nbsp;the&nbsp;example&nbsp;is&nbsp;a&nbsp;complete&nbsp;program,[1]&nbsp;<BR>&nbsp;and&nbsp;if&nbsp;you&nbsp;feed&nbsp;it&nbsp;to&nbsp;the&nbsp;Perl&nbsp;interpreter,&nbsp;it&nbsp;will&nbsp;print&nbsp;&amp;quot;&lt;TT&gt;Howdy,&nbsp;<BR>&nbsp;world!&lt;/TT&gt;&amp;quot;&nbsp;on&nbsp;your&nbsp;screen.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;BLOCKQUOTE&nbsp;class=footnote&gt;&nbsp;<BR>&nbsp;&lt;P&gt;[1]&nbsp;Or&nbsp;script,&nbsp;or&nbsp;application,&nbsp;or&nbsp;executable,&nbsp;or&nbsp;doohickey.&nbsp;Whatever.&nbsp;<BR>&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&lt;/BLOCKQUOTE&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;And&nbsp;that's&nbsp;that.&nbsp;You&nbsp;don't&nbsp;have&nbsp;to&nbsp;say&nbsp;much&nbsp;&lt;I&gt;after&lt;/I&gt;&nbsp;you&nbsp;say&nbsp;what&nbsp;<BR>&nbsp;you&nbsp;want&nbsp;to&nbsp;say,&nbsp;either.&nbsp;Unlike&nbsp;many&nbsp;languages,&nbsp;Perl&nbsp;thinks&nbsp;that&nbsp;falling&nbsp;<BR>&nbsp;off&nbsp;the&nbsp;end&nbsp;of&nbsp;your&nbsp;program&nbsp;is&nbsp;just&nbsp;a&nbsp;normal&nbsp;way&nbsp;to&nbsp;exit&nbsp;the&nbsp;program.&nbsp;You&nbsp;<BR>&nbsp;certainly&nbsp;&lt;I&gt;may&lt;/I&gt;&nbsp;call&nbsp;the&nbsp;&lt;A&nbsp;HREF=&quot;ch03_02.htm#PERL2-CMD-EXIT&quot;&gt;exit&lt;/A&gt;&nbsp;<BR>&nbsp;function&nbsp;explicitly&nbsp;if&nbsp;you&nbsp;wish,&nbsp;just&nbsp;as&nbsp;you&nbsp;&lt;I&gt;may&lt;/I&gt;&nbsp;declare&nbsp;some&nbsp;of&nbsp;<BR>&nbsp;your&nbsp;variables&nbsp;and&nbsp;subroutines,&nbsp;or&nbsp;even&nbsp;&lt;I&gt;force&lt;/I&gt;&nbsp;yourself&nbsp;to&nbsp;declare&nbsp;<BR>&nbsp;all&nbsp;your&nbsp;variables&nbsp;and&nbsp;subroutines.&nbsp;But&nbsp;it's&nbsp;your&nbsp;choice.&nbsp;With&nbsp;Perl&nbsp;you're&nbsp;<BR>&nbsp;free&nbsp;to&nbsp;do&nbsp;The&nbsp;Right&nbsp;Thing,&nbsp;however&nbsp;you&nbsp;care&nbsp;to&nbsp;define&nbsp;it.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;There&nbsp;are&nbsp;many&nbsp;other&nbsp;reasons&nbsp;why&nbsp;Perl&nbsp;is&nbsp;easy&nbsp;to&nbsp;use,&nbsp;but&nbsp;it&nbsp;would&nbsp;be&nbsp;<BR>&nbsp;pointless&nbsp;to&nbsp;list&nbsp;them&nbsp;all&nbsp;here,&nbsp;because&nbsp;that's&nbsp;what&nbsp;the&nbsp;rest&nbsp;of&nbsp;the&nbsp;book&nbsp;<BR>&nbsp;is&nbsp;for.&nbsp;The&nbsp;devil&nbsp;may&nbsp;be&nbsp;in&nbsp;the&nbsp;details,&nbsp;as&nbsp;they&nbsp;say,&nbsp;but&nbsp;Perl&nbsp;tries&nbsp;to&nbsp;<BR>&nbsp;help&nbsp;you&nbsp;out&nbsp;down&nbsp;there&nbsp;in&nbsp;the&nbsp;hot&nbsp;place&nbsp;too.&nbsp;At&nbsp;every&nbsp;level,&nbsp;Perl&nbsp;is&nbsp;about&nbsp;<BR>&nbsp;helping&nbsp;you&nbsp;get&nbsp;from&nbsp;here&nbsp;to&nbsp;there&nbsp;with&nbsp;minimum&nbsp;fuss&nbsp;and&nbsp;maximum&nbsp;enjoyment.&nbsp;<BR>&nbsp;That's&nbsp;why&nbsp;so&nbsp;many&nbsp;Perl&nbsp;programmers&nbsp;go&nbsp;around&nbsp;with&nbsp;a&nbsp;silly&nbsp;grin&nbsp;on&nbsp;their&nbsp;<BR>&nbsp;face.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;This&nbsp;chapter&nbsp;is&nbsp;an&nbsp;overview&nbsp;of&nbsp;Perl,&nbsp;so&nbsp;we're&nbsp;not&nbsp;trying&nbsp;to&nbsp;present&nbsp;<BR>&nbsp;Perl&nbsp;to&nbsp;the&nbsp;rational&nbsp;side&nbsp;of&nbsp;your&nbsp;brain.&nbsp;Nor&nbsp;are&nbsp;we&nbsp;trying&nbsp;to&nbsp;be&nbsp;complete,&nbsp;<BR>&nbsp;or&nbsp;logical.&nbsp;That's&nbsp;what&nbsp;the&nbsp;next&nbsp;chapter&nbsp;is&nbsp;for.[2]&nbsp;This&nbsp;chapter&nbsp;presents&nbsp;<BR>&nbsp;Perl&nbsp;to&nbsp;the&nbsp;&lt;I&gt;other&lt;/I&gt;&nbsp;side&nbsp;of&nbsp;your&nbsp;brain,&nbsp;whether&nbsp;you&nbsp;prefer&nbsp;to&nbsp;call&nbsp;<BR>&nbsp;it&nbsp;associative,&nbsp;artistic,&nbsp;passionate,&nbsp;or&nbsp;merely&nbsp;spongy.&nbsp;To&nbsp;that&nbsp;end,&nbsp;we'll&nbsp;<BR>&nbsp;be&nbsp;presenting&nbsp;various&nbsp;views&nbsp;of&nbsp;Perl&nbsp;that&nbsp;will&nbsp;hopefully&nbsp;give&nbsp;you&nbsp;as&nbsp;clear&nbsp;<BR>&nbsp;a&nbsp;picture&nbsp;of&nbsp;Perl&nbsp;as&nbsp;the&nbsp;blind&nbsp;men&nbsp;had&nbsp;of&nbsp;the&nbsp;elephant.&nbsp;Well,&nbsp;okay,&nbsp;maybe&nbsp;<BR>&nbsp;we&nbsp;can&nbsp;do&nbsp;better&nbsp;than&nbsp;that.&nbsp;We're&nbsp;dealing&nbsp;with&nbsp;a&nbsp;camel&nbsp;here.&nbsp;Hopefully,&nbsp;<BR>&nbsp;at&nbsp;least&nbsp;one&nbsp;of&nbsp;these&nbsp;views&nbsp;of&nbsp;Perl&nbsp;will&nbsp;help&nbsp;get&nbsp;you&nbsp;over&nbsp;the&nbsp;hump.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;BLOCKQUOTE&nbsp;class=footnote&gt;&nbsp;<BR>&nbsp;&lt;P&gt;[2]&nbsp;Vulcans&nbsp;(and&nbsp;like-minded&nbsp;humans)&nbsp;should&nbsp;skip&nbsp;this&nbsp;overview&nbsp;and&nbsp;go&nbsp;<BR>&nbsp;straight&nbsp;to&nbsp;&lt;A&nbsp;HREF=&quot;ch02_01.htm&quot;&gt;Chapter&nbsp;2,&nbsp;&lt;I&gt;The&nbsp;Gory&nbsp;Details&lt;/I&gt;&lt;/A&gt;,&nbsp;<BR>&nbsp;for&nbsp;maximum&nbsp;information&nbsp;density.&nbsp;If,&nbsp;on&nbsp;the&nbsp;other&nbsp;hand,&nbsp;you're&nbsp;looking&nbsp;<BR>&nbsp;for&nbsp;a&nbsp;carefully&nbsp;paced&nbsp;tutorial,&nbsp;you&nbsp;should&nbsp;probably&nbsp;get&nbsp;Randal's&nbsp;nice&nbsp;book,&nbsp;<BR>&nbsp;&lt;I&gt;Learning&nbsp;Perl&lt;/I&gt;&nbsp;(published&nbsp;by&nbsp;O'Reilly&nbsp;&amp;amp;&nbsp;Associates).&nbsp;But&nbsp;don't&nbsp;<BR>&nbsp;throw&nbsp;out&nbsp;this&nbsp;book&nbsp;just&nbsp;yet.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&lt;/BLOCKQUOTE&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;H2&gt;&lt;A&nbsp;NAME=&quot;PERL2-CH-1-SECT-2&quot;&gt;&lt;/A&gt;1.2&nbsp;Natural&nbsp;and&nbsp;Artificial&nbsp;Languages&lt;/H2&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;P&gt;&lt;A&nbsp;NAME=&quot;CH01.LANG&quot;&gt;&lt;/A&gt;&lt;A&nbsp;NAME=&quot;CH01.NAT&quot;&gt;&lt;/A&gt;&lt;A&nbsp;NAME=&quot;CH01.ART&quot;&gt;&lt;/A&gt;Languages&nbsp;<BR>&nbsp;were&nbsp;first&nbsp;invented&nbsp;by&nbsp;humans,&nbsp;for&nbsp;the&nbsp;benefit&nbsp;of&nbsp;humans.&nbsp;In&nbsp;the&nbsp;annals&nbsp;<BR>&nbsp;of&nbsp;computer&nbsp;science,&nbsp;this&nbsp;fact&nbsp;has&nbsp;occasionally&nbsp;been&nbsp;forgotten.[3]&nbsp;Since&nbsp;<BR>&nbsp;Perl&nbsp;was&nbsp;designed&nbsp;(loosely&nbsp;speaking)&nbsp;by&nbsp;an&nbsp;occasional&nbsp;linguist,&nbsp;it&nbsp;was&nbsp;<BR>&nbsp;designed&nbsp;to&nbsp;work&nbsp;smoothly&nbsp;in&nbsp;the&nbsp;same&nbsp;ways&nbsp;that&nbsp;natural&nbsp;language&nbsp;works&nbsp;<BR>&nbsp;smoothly.&nbsp;Naturally,&nbsp;there&nbsp;are&nbsp;many&nbsp;aspects&nbsp;to&nbsp;this,&nbsp;since&nbsp;natural&nbsp;language&nbsp;<BR>&nbsp;works&nbsp;well&nbsp;at&nbsp;many&nbsp;levels&nbsp;simultaneously.&nbsp;We&nbsp;could&nbsp;enumerate&nbsp;many&nbsp;of&nbsp;these&nbsp;<BR>&nbsp;linguistic&nbsp;principles&nbsp;here,&nbsp;but&nbsp;the&nbsp;most&nbsp;important&nbsp;principle&nbsp;of&nbsp;language&nbsp;<BR>&nbsp;design&nbsp;is&nbsp;simply&nbsp;that&nbsp;easy&nbsp;things&nbsp;should&nbsp;be&nbsp;easy,&nbsp;and&nbsp;hard&nbsp;things&nbsp;should&nbsp;<BR>&nbsp;be&nbsp;possible.&nbsp;That&nbsp;may&nbsp;seem&nbsp;obvious,&nbsp;but&nbsp;many&nbsp;computer&nbsp;languages&nbsp;fail&nbsp;at&nbsp;<BR>&nbsp;one&nbsp;or&nbsp;the&nbsp;other.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&nbsp;<BR>&nbsp;&lt;BLOCKQUOTE&nbsp;class=footnote&gt;&nbsp;<BR>&nbsp;&lt;P&gt;[3]&nbsp;More&nbsp;precisely,&nbsp;this&nbsp;fact&nbsp;has&nbsp;occasionally&nbsp;been&nbsp;remembered.&nbsp;&lt;/P&gt;&nbsp;<BR>&nbsp;&lt;/BLOCKQUOTE&gt;&nbsp;<BR>
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