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📄 pattern matching.mht

📁 Perl 编程技巧大全。适合初学者阅读。
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#Ren=E9e
#Moli=E8re
#h=E6moglobin
#na=EFve
#tsch=FC=DF
#random!stuff#here
#-----------------------------
</FONT></PRE></FONT></TD></TR></TBODY></TABLE></DIV>
<DIV class=3DSECT2>
<H2 class=3DSECT2><A name=3DAEN294>Matching Words</A></H2>
<TABLE width=3D"100%" bgColor=3D#2f4f4f border=3D0>
  <TBODY>
  <TR>
    <TD><PRE class=3DSCREEN><FONT color=3D#f5deb3 size=3D+1><FONT =
color=3D#bebebe>#-----------------------------
#/\S+/               # as many non-whitespace bytes as possible
#/[A-Za-z'-]+/       # as many letters, apostrophes, and hyphens
#-----------------------------
#/\b([A-Za-z]+)\b/            # usually best
#/\s([A-Za-z]+)\s/            # fails at ends or w/ punctuation
#-----------------------------
</FONT></PRE></FONT></TD></TR></TBODY></TABLE></DIV>
<DIV class=3DSECT2>
<H2 class=3DSECT2><A name=3DAEN297>Commenting Regular =
Expressions</A></H2>
<TABLE width=3D"100%" bgColor=3D#2f4f4f border=3D0>
  <TBODY>
  <TR>
    <TD><PRE class=3DSCREEN><FONT color=3D#f5deb3 size=3D+1><FONT =
color=3D#bebebe>#-----------------------------
# <FONT size=3D-1><A =
href=3D"http://pleac.sourceforge.net/include/perl/ch06/resname">download =
the following standalone program</A></FONT>
#!/usr/bin/perl -p
# resname - change all "foo.bar.com" style names in the input stream
# into "foo.bar.com [204.148.40.9]" (or whatever) instead
</FONT>
<FONT color=3D#ffa500>use</FONT> <FONT =
color=3D#b2dfee>Socket</FONT><FONT color=3D#00ffff>;</FONT>              =
   <FONT color=3D#bebebe># load inet_addr
</FONT><FONT color=3D#ff7f50>s</FONT><FONT color=3D#00ffff>{</FONT>      =
                    <FONT color=3D#bebebe>#
</FONT>    <FONT color=3D#00ffff>(</FONT>                       <FONT =
color=3D#bebebe># capture the hostname in $1
</FONT>        <FONT color=3D#00ffff>(</FONT>?:                 <FONT =
color=3D#bebebe># these parens for grouping only
</FONT>            <FONT color=3D#00ffff>(</FONT>?! <FONT =
color=3D#00ffff>[</FONT>-_<FONT color=3D#00ffff>]</FONT>  <FONT =
color=3D#00ffff>)</FONT>     <FONT color=3D#bebebe># lookahead for =
neither underscore nor dash
</FONT>            <FONT color=3D#00ffff>[</FONT>\w-<FONT =
color=3D#00ffff>]</FONT> +         <FONT color=3D#bebebe># hostname =
component
</FONT>            \.              <FONT color=3D#bebebe># and the =
domain dot
</FONT>        <FONT color=3D#00ffff>)</FONT> +                 <FONT =
color=3D#bebebe># now repeat that whole thing a bunch of times
</FONT>        <FONT color=3D#00ffff>[</FONT>A-Za<FONT =
color=3D#b2dfee>-z</FONT><FONT color=3D#00ffff>]</FONT>            <FONT =
color=3D#bebebe># next must be a letter
</FONT>        <FONT color=3D#00ffff>[</FONT>\w-<FONT =
color=3D#00ffff>]</FONT> +             <FONT color=3D#bebebe># now =
trailing domain part
</FONT>    <FONT color=3D#00ffff>)</FONT>                       <FONT =
color=3D#bebebe># end of $1 capture
</FONT><FONT color=3D#00ffff>}{</FONT>                          <FONT =
color=3D#bebebe># replace with this:
</FONT>    <FONT color=3D#00cd00>"$1 "</FONT> .                 <FONT =
color=3D#bebebe># the original bit, plus a space
</FONT>           <FONT color=3D#00ffff>(</FONT> <FONT =
color=3D#00ffff>(</FONT>$addr =3D <FONT =
color=3D#98fb98>gethostbyname</FONT><FONT color=3D#00ffff>(</FONT>$<FONT =
color=3D#cdcd00>1</FONT><FONT color=3D#00ffff>))</FONT>   <FONT =
color=3D#bebebe># if we get an addr
</FONT>            ? <FONT color=3D#00cd00>"["</FONT> . inet_ntoa<FONT =
color=3D#00ffff>(</FONT>$addr<FONT color=3D#00ffff>)</FONT> . <FONT =
color=3D#00cd00>"]"</FONT> <FONT color=3D#bebebe>#        format it
</FONT>            : <FONT color=3D#00cd00>"[???]"</FONT>                =
      <FONT color=3D#bebebe># else mark dubious
</FONT>           <FONT color=3D#00ffff>)</FONT>
<FONT color=3D#00ffff>}</FONT>gex<FONT color=3D#00ffff>;</FONT>          =
     <FONT color=3D#bebebe># /g for global
</FONT>                    <FONT color=3D#bebebe># /e for execute
</FONT>                    <FONT color=3D#bebebe># /x for nice =
formatting
</FONT>
<FONT color=3D#bebebe>#-----------------------------
</FONT><FONT color=3D#ff7f50>s</FONT>/                  <FONT =
color=3D#bebebe># replace
</FONT>  \#                <FONT color=3D#bebebe>#   a pound sign
</FONT>  <FONT color=3D#00ffff>(</FONT>\w+<FONT color=3D#00ffff>)</FONT> =
            <FONT color=3D#bebebe>#   the variable name
</FONT>  \#                <FONT color=3D#bebebe>#   another pound sign
</FONT>/$<FONT color=3D#00ffff>{</FONT>$<FONT =
color=3D#cdcd00>1</FONT><FONT color=3D#00ffff>}</FONT>/xg<FONT =
color=3D#00ffff>;</FONT>          <FONT color=3D#bebebe># with the value =
of the global variable
##-----------------------------
</FONT><FONT color=3D#ff7f50>s</FONT>/                  <FONT =
color=3D#bebebe># replace
</FONT>\#                  <FONT color=3D#bebebe>#   a pound sign
</FONT><FONT color=3D#00ffff>(</FONT>\w+<FONT color=3D#00ffff>)</FONT>   =
            <FONT color=3D#bebebe>#   the variable name
</FONT>\#                  <FONT color=3D#bebebe>#   another pound sign
</FONT>/<FONT color=3D#00cd00>'$' . $1/xeeg;     # '</FONT> with the =
value of *any* variable
<FONT color=3D#bebebe>#-----------------------------
</FONT></PRE></FONT></TD></TR></TBODY></TABLE></DIV>
<DIV class=3DSECT2>
<H2 class=3DSECT2><A name=3DAEN300>Finding the Nth Occurrence of a =
Match</A></H2>
<TABLE width=3D"100%" bgColor=3D#2f4f4f border=3D0>
  <TBODY>
  <TR>
    <TD><PRE class=3DSCREEN><FONT color=3D#f5deb3 size=3D+1><FONT =
color=3D#bebebe>#-----------------------------
# One fish two fish red fish blue fish
#-----------------------------
</FONT>$WANT =3D <FONT color=3D#cdcd00>3</FONT><FONT =
color=3D#00ffff>;</FONT>
$count =3D <FONT color=3D#cdcd00>0</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#ffa500>while</FONT> <FONT color=3D#00ffff>(</FONT>/<FONT =
color=3D#00ffff>(</FONT>\w+<FONT =
color=3D#00ffff>)</FONT>\s+fish\b/gi<FONT color=3D#00ffff>)</FONT> <FONT =
color=3D#00ffff>{</FONT>
    <FONT color=3D#ffa500>if</FONT> <FONT =
color=3D#00ffff>(</FONT>++$count =3D=3D $WANT<FONT =
color=3D#00ffff>)</FONT> <FONT color=3D#00ffff>{</FONT>
        <FONT color=3D#ff7f50>print</FONT> <FONT color=3D#00cd00>"The =
third fish is a $1 one.\n"</FONT><FONT color=3D#00ffff>;</FONT>
        <FONT color=3D#bebebe># Warning: don't `last' out of this loop
</FONT>    <FONT color=3D#00ffff>}</FONT>
<FONT color=3D#00ffff>}</FONT>
<FONT color=3D#bebebe># The third fish is a red one.
#-----------------------------
</FONT>/<FONT color=3D#00ffff>(</FONT>?:\w+\s+fish\s+<FONT =
color=3D#00ffff>){</FONT><FONT color=3D#cdcd00>2</FONT><FONT =
color=3D#00ffff>}(</FONT>\w+<FONT color=3D#00ffff>)</FONT>\s+fish/i<FONT =
color=3D#00ffff>;</FONT>
<FONT color=3D#bebebe>#-----------------------------
# simple way with while loop
</FONT>$count =3D <FONT color=3D#cdcd00>0</FONT><FONT =
color=3D#00ffff>;</FONT>
<FONT color=3D#ffa500>while</FONT> <FONT color=3D#00ffff>(</FONT>$string =
=3D~ /PAT/g<FONT color=3D#00ffff>)</FONT> <FONT color=3D#00ffff>{</FONT>
    $count++<FONT color=3D#00ffff>;</FONT>               <FONT =
color=3D#bebebe># or whatever you'd like to do here
</FONT><FONT color=3D#00ffff>}</FONT>

<FONT color=3D#bebebe># same thing with trailing while
</FONT>$count =3D <FONT color=3D#cdcd00>0</FONT><FONT =
color=3D#00ffff>;</FONT>
$count++ <FONT color=3D#ffa500>while</FONT> $string =3D~ /PAT/g<FONT =
color=3D#00ffff>;</FONT>

<FONT color=3D#bebebe># or with for loop
</FONT><FONT color=3D#ffa500>for</FONT> <FONT =
color=3D#00ffff>(</FONT>$count =3D <FONT color=3D#cdcd00>0</FONT><FONT =
color=3D#00ffff>;</FONT> $string =3D~ /PAT/g<FONT =
color=3D#00ffff>;</FONT> $count++<FONT color=3D#00ffff>)</FONT> <FONT =
color=3D#00ffff>{</FONT> <FONT color=3D#00ffff>}</FONT>
<FONT color=3D#43cd80>    </FONT>
<FONT color=3D#bebebe># Similar, but this time count overlapping matches
</FONT>$count++ <FONT color=3D#ffa500>while</FONT> $string =3D~ /<FONT =
color=3D#00ffff>(</FONT>?=3DPAT<FONT color=3D#00ffff>)</FONT>/g<FONT =
color=3D#00ffff>;</FONT>
<FONT color=3D#bebebe>#-----------------------------
</FONT>$pond  =3D <FONT color=3D#00cd00>'One fish two fish red fish blue =
fish'</FONT><FONT color=3D#00ffff>;</FONT>

<FONT color=3D#bebebe># using a temporary
</FONT><FONT color=3D#cdad00>@colors</FONT> =3D <FONT =
color=3D#00ffff>(</FONT>$pond =3D~ /<FONT =
color=3D#00ffff>(</FONT>\w+<FONT =
color=3D#00ffff>)</FONT>\s+fish\b/gi<FONT color=3D#00ffff>);</FONT>      =
<FONT color=3D#bebebe># get all matches
</FONT>$color  =3D <FONT color=3D#cdad00>$colors</FONT><FONT =
color=3D#00ffff>[</FONT><FONT color=3D#cdcd00>2</FONT><FONT =
color=3D#00ffff>];</FONT>                         <FONT =
color=3D#bebebe># then the one we want
</FONT>
<FONT color=3D#bebebe># or without a temporary array
</FONT>$color =3D <FONT color=3D#00ffff>(</FONT> $pond =3D~ /<FONT =
color=3D#00ffff>(</FONT>\w+<FONT color=3D#00ffff>)</FONT>\s+fish\b/gi =
<FONT color=3D#00ffff>)[</FONT><FONT color=3D#cdcd00>2</FONT><FONT =
color=3D#00ffff>];</FONT>  <FONT color=3D#bebebe># just grab element 3
</FONT>
<FONT color=3D#ff7f50>print</FONT> <FONT color=3D#00cd00>"The third fish =
in the pond is $color.\n"</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#bebebe># The third fish in the pond is red.
#-----------------------------
</FONT>$count =3D <FONT color=3D#cdcd00>0</FONT><FONT =
color=3D#00ffff>;</FONT>
$_ =3D <FONT color=3D#00cd00>'One fish two fish red fish blue =
fish'</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#cdad00>@evens</FONT> =3D <FONT =
color=3D#ff7f50>grep</FONT> <FONT color=3D#00ffff>{</FONT> $count++ % =
<FONT color=3D#cdcd00>2</FONT> =3D=3D <FONT color=3D#cdcd00>1</FONT> =
<FONT color=3D#00ffff>}</FONT> /<FONT color=3D#00ffff>(</FONT>\w+<FONT =
color=3D#00ffff>)</FONT>\s+fish\b/gi<FONT color=3D#00ffff>;</FONT>
<FONT color=3D#ff7f50>print</FONT> <FONT color=3D#00cd00>"Even numbered =
fish are </FONT><FONT color=3D#cdad00>@evens</FONT><FONT =
color=3D#00cd00>.\n"</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#bebebe># Even numbered fish are two blue.
#-----------------------------
</FONT>$count =3D <FONT color=3D#cdcd00>0</FONT><FONT =
color=3D#00ffff>;</FONT>
<FONT color=3D#ff7f50>s</FONT><FONT color=3D#00ffff>{</FONT>
   \b               <FONT color=3D#bebebe># makes next \w more efficient
</FONT>   <FONT color=3D#00ffff>(</FONT> \w+ <FONT =
color=3D#00ffff>)</FONT>          <FONT color=3D#bebebe># this is what =
we'll be changing
</FONT>   <FONT color=3D#00ffff>(</FONT>
     \s+ fish \b
   <FONT color=3D#00ffff>)</FONT>
<FONT color=3D#00ffff>}{</FONT>
    <FONT color=3D#ffa500>if</FONT> <FONT =
color=3D#00ffff>(</FONT>++$count =3D=3D <FONT =
color=3D#cdcd00>4</FONT><FONT color=3D#00ffff>)</FONT> <FONT =
color=3D#00ffff>{</FONT>
        <FONT color=3D#00cd00>"sushi"</FONT> . $<FONT =
color=3D#cdcd00>2</FONT><FONT color=3D#00ffff>;</FONT>
    <FONT color=3D#00ffff>}</FONT> <FONT color=3D#ffa500>else</FONT> =
<FONT color=3D#00ffff>{</FONT>
         $<FONT color=3D#cdcd00>1</FONT>   . $<FONT =
color=3D#cdcd00>2</FONT><FONT color=3D#00ffff>;</FONT>
    <FONT color=3D#00ffff>}</FONT>
<FONT color=3D#00ffff>}</FONT>gex<FONT color=3D#00ffff>;</FONT>
<FONT color=3D#bebebe># One fish two fish red fish sushi fish
#-----------------------------
</FONT>$pond =3D <FONT color=3D#00cd00>'One fish two fish red fish blue =
fish swim here.'</FONT><FONT color=3D#00ffff>;</FONT>
$color =3D <FONT color=3D#00ffff>(</FONT> $pond =3D~ /\b<FONT =
color=3D#00ffff>(</FONT>\w+<FONT color=3D#00ffff>)</FONT>\s+fish\b/gi =
<FONT color=3D#00ffff>)[</FONT><FONT color=3D#cdcd00>-1</FONT><FONT =
color=3D#00ffff>];</FONT>
<FONT color=3D#ff7f50>print</FONT> <FONT color=3D#00cd00>"Last fish is =
$color.\n"</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#bebebe># Last fish is blue.
#-----------------------------
</FONT><FONT color=3D#ff7f50>m</FONT><FONT color=3D#00ffff>{</FONT>
    A               <FONT color=3D#bebebe># find some pattern A
</FONT>    <FONT color=3D#00ffff>(</FONT>?!             <FONT =
color=3D#bebebe># mustn't be able to find
</FONT>        .*          <FONT color=3D#bebebe># something
</FONT>        A           <FONT color=3D#bebebe># and A
</FONT>    <FONT color=3D#00ffff>)</FONT>
    $               <FONT color=3D#bebebe># through the end of the =
string
</FONT><FONT color=3D#00ffff>}</FONT><FONT color=3D#98fb98>x</FONT>
<FONT color=3D#bebebe>#-----------------------------
</FONT>$pond =3D <FONT color=3D#00cd00>'One fish two fish red fish blue =
fish swim here.'</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#ffa500>if</FONT> <FONT color=3D#00ffff>(</FONT>$pond =3D~ =
<FONT color=3D#ff7f50>m</FONT><FONT color=3D#00ffff>{</FONT>
                    \b  <FONT color=3D#00ffff>(</FONT>  \w+<FONT =
color=3D#00ffff>)</FONT> \s+ fish \b
                <FONT color=3D#00ffff>(</FONT>?! .* \b fish \b <FONT =
color=3D#00ffff>)</FONT>
            <FONT color=3D#00ffff>}</FONT>six <FONT =
color=3D#00ffff>)</FONT>
<FONT color=3D#00ffff>{</FONT>
    <FONT color=3D#ff7f50>print</FONT> <FONT color=3D#00cd00>"Last fish =
is $1.\n"</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#00ffff>}</FONT> <FONT color=3D#ffa500>else</FONT> <FONT =
color=3D#00ffff>{</FONT>
    <FONT color=3D#ff7f50>print</FONT> <FONT =
12345

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