ch06_07.htm

By Tom Christiansen and Nathan Torkington ISBN 1-56592-243-3 First Edition, published August 1998

>Chemisery&quot;</CODE
>. It wraps these with an appropriate HTML level one header. Because the pattern is relatively complex, we use the <CODE
CLASS="literal"
>/x</CODE
> modifier so we can embed whitespace and comments.</P
><DIV
CLASS="example"
><H4
CLASS="example"
><A
CLASS="title"
NAME="ch06-31611"
>Example 6.3: headerfy</A
></H4
><PRE
CLASS="programlisting"
>#!/usr/bin/perl
# <A
CLASS="indexterm"
NAME="ch06-idx-1000007793-0"
></A
>headerfy: change certain chapter headers to html
$/ = '';
while ( &lt;&gt; ) {              # fetch a paragraph
    s{
        \A                  # start of record
        (                   # capture in $1
            Chapter         # text string
            \s+             # mandatory whitespace
            \d+             # decimal number
            \s*             # optional whitespace
            :               # a real colon
            . *             # anything not a newline till end of line
        )
    }{&lt;H1&gt;$1&lt;/H1&gt;}gx;
    print;
}</PRE
></DIV
><P
CLASS="para"
>Here it is as a one-liner from the command line if those extended comments just get in the way of understanding:</P
><PRE
CLASS="programlisting"
>% perl -00pe 's{\A(Chapter\s+\d+\s*:.*)}{&lt;H1&gt;$1&lt;/H1&gt;}gx' datafile</PRE
><P
CLASS="para"
>This problem is interesting because we need to be able to specify both start-of-record and end-of-line in the same pattern. We could normally use <CODE
CLASS="literal"
>^</CODE
> for start-of-record, but we need <CODE
CLASS="literal"
>$</CODE
> to indicate not only end-of-record, but also end-of-line as well. We add the <CODE
CLASS="literal"
>/m</CODE
> modifier, which changes both <CODE
CLASS="literal"
>^</CODE
> and <CODE
CLASS="literal"
>$</CODE
>. So instead of using <CODE
CLASS="literal"
>^</CODE
> to match beginning-of-record, we use <CODE
CLASS="literal"
>\A</CODE
> instead. (We're not using it here, but in case you're interested, the version of <CODE
CLASS="literal"
>$</CODE
> that always matches end-of-record even in the presence of <CODE
CLASS="literal"
>/m</CODE
> is <CODE
CLASS="literal"
>\Z</CODE
>.)</P
><P
CLASS="para"
>The following example demonstrates using both <CODE
CLASS="literal"
>/s</CODE
> and <CODE
CLASS="literal"
>/m</CODE
> together. That's because we want <CODE
CLASS="literal"
>^</CODE
> to match the beginning of any line in the paragraph and also want dot to be able to match a newline. (Because they are unrelated, using them together is simply the sum of the parts. If you have the questionable habit of using "single line" as a mnemonic for <CODE
CLASS="literal"
>/s</CODE
> and "multiple line" for <CODE
CLASS="literal"
>/m </CODE
>, then you may think you can't use them together.) The predefined variable <CODE
CLASS="literal"
>$.</CODE
> represents the record number of the last read file. The predefined variable <CODE
CLASS="literal"
>$ARGV</CODE
> is the file automatically opened by implicit <CODE
CLASS="literal"
>&lt;ARGV&gt;</CODE
> processing.</P
><PRE
CLASS="programlisting"
>$/ = '';            # paragraph read mode for readline access
while (&lt;ARGV&gt;) {
    while (m#^START(.*?)^END#sm) {  # /s makes . span line boundaries
                                    # /m makes ^ match near newlines
        print &quot;chunk $. in $ARGV has &lt;&lt;$1&gt;&gt;\n&quot;;
    }
}</PRE
><P
CLASS="para"
>If you've already committed to using the <CODE
CLASS="literal"
>/m</CODE
> modifier, you can use <CODE
CLASS="literal"
>\A</CODE
> and <CODE
CLASS="literal"
>\Z</CODE
> to get the old meanings of <CODE
CLASS="literal"
>^</CODE
> and <CODE
CLASS="literal"
>$</CODE
> respectively. But what if you've used the <CODE
CLASS="literal"
>/s</CODE
> modifier and want to get the original meaning of <CODE
CLASS="literal"
>.</CODE
>? You can use <CODE
CLASS="literal"
>[^\n]</CODE
>. If you don't care to use <CODE
CLASS="literal"
>/s</CODE
> but want the notion of matching any character, you could construct a character class that matches any one byte, such as <CODE
CLASS="literal"
>[\000-\377]</CODE
> or even <CODE
CLASS="literal"
>[\d\D]</CODE
>. You can't use <CODE
CLASS="literal"
>[.\n]</CODE
> because <CODE
CLASS="literal"
>.</CODE
> is not special in a character <CODE
CLASS="literal"
></CODE
><A
CLASS="indexterm"
NAME="ch06-idx-1000007584-0"
></A
><A
CLASS="indexterm"
NAME="ch06-idx-1000007584-1"
></A
>class.<A
CLASS="indexterm"
NAME="ch06-idx-1000007573-0"
></A
><A
CLASS="indexterm"
NAME="ch06-idx-1000007573-1"
></A
><A
CLASS="indexterm"
NAME="ch06-idx-1000007573-2"
></A
><A
CLASS="indexterm"
NAME="ch06-idx-1000007573-3"
></A
></P
></DIV
><DIV
CLASS="sect2"
><H3
CLASS="sect2"
><A
CLASS="title"
NAME="ch06-pgfId-855"
>See Also</A
></H3
><P
CLASS="para"
>The <CODE
CLASS="literal"
>$/</CODE
> variable in <I
CLASS="filename"
>perlvar  </I
>(1) and in the <A
CLASS="olink"
HREF="../prog/ch02_09.htm"
>"Special Variables"</A
> section of <A
CLASS="olink"
HREF="../prog/ch02_01.htm"
>Chapter 2</A
> of <A
CLASS="citetitle"
HREF="../prog/index.htm"
TITLE="Programming Perl"
><CITE
CLASS="citetitle"
>Programming Perl</CITE
></A
>; the <CODE
CLASS="literal"
>/s</CODE
> and <CODE
CLASS="literal"
>/m</CODE
> modifiers in <I
CLASS="filename"
>perlre </I
>(1) and <A
CLASS="olink"
HREF="../prog/ch02_04.htm#PERL2-CH-2-SECT-4.1.3"
>"the fine print"</A
> section of <A
CLASS="olink"
HREF="../prog/ch02_01.htm"
>Chapter 2</A
> of <A
CLASS="citetitle"
HREF="../prog/index.htm"
TITLE="Programming Perl"
><CITE
CLASS="citetitle"
>Programming Perl</CITE
></A
>; the "String Anchors" section of <CITE
CLASS="citetitle"
>Mastering Regular Expressions</CITE
>; we talk more about the special variable <CODE
CLASS="literal"
>$/</CODE
> in <A
CLASS="xref"
HREF="ch08_01.htm"
TITLE="File Contents"
>Chapter 8</A
></P
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