Regex_Cookbook_2_Code_Samples.html

<h4>Tags that contain “my-class” within their class attribute
        value</h4>
<pre>&lt;(?:[^&gt;"']|"[^"]*"|'[^']*')+&gt;</pre>
<p>Regex options: None<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>^(?:[^&gt;"']|"[^"]*"|'[^']*')+?\sclass\s*=\s*("[^"]*"|'[^']*')</pre>
<p>Regex options: Case
          insensitive<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>["'\s]my-class["'\s]</pre>
<p>Regex options: None<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>(?:^|\s)my-class(?:\s|$)</pre>
<p>Regex options: None<br>
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h2>9.8. Add a cellspacing Attribute to &lt;table&gt; Tags That Do Not
    Already Include It</h2>
<h3>Solution</h3>
<h4>Solution 1, simplistic</h4>
<pre>&lt;table\b(?![^&gt;]*?\scellspacing\b)([^&gt;]*)&gt;</pre>
<p>Regex options: Case
          insensitive<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>&lt;table \b            # Match "&lt;table", as a complete word
(?!                  # Not followed by:
  [^&gt;]*?             #   Any attributes, etc.
  \s cellspacing \b  #   "cellspacing", as a complete word
)
([^&gt;]*)              # Capture attributes, etc. to backreference 1
&gt;</pre>
<p>Regex options: Case
          insensitive<br>
Regex flavors: .NET,
          Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<h4>Solution 2, more reliable</h4>
<pre>&lt;table\b(?!(?:[^&gt;"']|"[^"]*"|'[^']*')*?\scellspacing\b)((?:[^&gt;"']|"[^"]*"|'[^']*')*)&gt;</pre>
<p>Regex options: Case
          insensitive<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>&lt;table \b  # Match "&lt;table", as a complete word
(?!  # Not followed by: Any attributes, etc., then "cellspacing"
  (?:[^&gt;"']|"[^"]*"|'[^']*')*?
  \s cellspacing \b
)
(  # Capture attributes, etc. to backreference 1
  (?:[^&gt;"']|"[^"]*"|'[^']*')*
)
&gt;</pre>
<p>Regex options: Case
          insensitive<br>
Regex flavors: .NET,
          Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<h4>Insert the new attribute</h4>
<pre>&lt;table cellspacing="0"$1&gt;</pre>
<pre>&lt;table cellspacing="0"\1&gt;</pre>
<h2>9.9. Remove XML-Style Comments</h2>
<h3>Solution</h3>
<pre>&lt;!--.*?--&gt;</pre>
<p>Regex options: Dot
        matches line breaks<br>
Regex flavors: .NET,
        Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<pre>&lt;!--[\s\S]*?--&gt;</pre>
<p>Regex options: None<br>
</p><h3>Discussion</h3>
<h4>When comments can’t be removed</h4>
<pre>&lt;(script|style|textarea|title|xmp)\b(?:[^&gt;"']|"[^"]*"|'[^']*')*&gt;.*?&lt;/\1\s*&gt;|&lt;plaintext\b(?:[^&gt;"']|"[^"]*"|'[^']*')*&gt;.*|&lt;[a-z](?:[^&gt;"']|"[^"]*"|'[^']*')*&gt;|&lt;!\[CDATA\[.*?]]&gt;</pre>
<p>Regex options: Case
          insensitive, dot matches line breaks<br>
Regex flavors: .NET,
          Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<pre># Special element: tag and its content
&lt;( script | style | textarea | title | xmp )\b
  (?:[^&gt;"']|"[^"]*"|'[^']*')*
&gt; .*? &lt;/\1\s*&gt;
|
# &lt;plaintext/&gt; continues until the end of the string
&lt;plaintext\b
  (?:[^&gt;"']|"[^"]*"|'[^']*')*
&gt; .*
|
# Standard element: tag only
&lt;[a-z]  # Tag name initial character
  (?:[^&gt;"']|"[^"]*"|'[^']*')*
&gt;
|
# CDATA section
&lt;!\[CDATA\[ .*? ]]&gt;</pre>
<p>Regex options: Case
          insensitive, dot matches line breaks, free-spacing<br>
Regex flavors: .NET,
          Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<pre>&lt;(script|style|textarea|title|xmp)\b(?:[^&gt;"']|"[^"]*"|'[^']*')*&gt;[\s\S]*?&lt;/\1\s*&gt;|&lt;plaintext\b(?:[^&gt;"']|"[^"]*"|'[^']*')*&gt;[\s\S]*|&lt;[a-z](?:[^&gt;"']|"[^"]*"|'[^']*')*&gt;|&lt;!\[CDATA\[[\s\S]*?]]&gt;</pre>
<p>Regex options: Case
          insensitive<br>
</p><h3>Variations</h3>
<h4>Find valid XML comments</h4>
<pre>&lt;!--[^-]*(?:-[^-]+)*--\s*&gt;</pre>
<p>Regex options: None<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>&lt;!--(?&gt;-?[^-]+)*--\s*&gt;</pre>
<p>Regex options: None<br>
Regex flavors: .NET,
          Java, PCRE, Perl, Ruby</p>
<h4>Find valid HTML comments</h4>
<pre>&lt;!--(?!-?&gt;)[^-]*(?:-[^-]+)*--&gt;</pre>
<p>Regex options: None<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h2>9.10. Find Words Within XML-Style Comments</h2>
<h3>Problem</h3>
<pre>        This "TODO" is not within a comment, but the next one is. &lt;!-- 
        TODO
        : Come up with a cooler comment for this example. --&gt;</pre>
<h3>Solution</h3>
<h4>Two-step approach</h4>
<pre>&lt;!--.*?--&gt;</pre>
<p>Regex options: Dot
          matches line breaks<br>
Regex flavors: .NET,
          Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<pre>&lt;!--[\s\S]*?--&gt;</pre>
<p>Regex options: None<br>
</p><pre>\bTODO\b</pre>
<p>Regex options: Case
          insensitive<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h4>Single-step approach</h4>
<pre>\bTODO\b(?=(?:(?!&lt;!--).)*?--&gt;)</pre>
<p>Regex options: Case
          insensitive, dot matches line breaks<br>
Regex flavors: .NET,
          Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<pre>\bTODO\b(?=(?:(?!&lt;!--)[\s\S])*?--&gt;)</pre>
<p>Regex options: Case
          insensitive<br>
</p><h3>Discussion</h3>
<h4>Single-step approach</h4>
<pre>\b TODO \b      # Match the characters "TODO", as a complete word
(?=             # Followed by:
  (?:           #   Group but don't capture:
    (?! &lt;!-- )  #     Not followed by: "&lt;!--"
    .           #     Match any single character
  )*?           #   Repeat zero or more times, as few as possible (lazy)
  --&gt;           #   Match the characters "--&gt;"
)</pre>
<p>Regex options: Dot
          matches line breaks, free-spacing<br>
Regex flavors: .NET,
          Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<h3>Variations</h3>
<pre>(?&lt;=&lt;!--(?:(?!--&gt;).)*?)\bTODO\b(?=(?:(?!&lt;!--).)*?--&gt;)</pre>
<p>Regex options: Case
        insensitive, dot matches line breaks<br>
</p><h2>9.11. Change the Delimiter Used in CSV Files</h2>
<h3>Solution</h3>
<pre>(,|\r?\n|^)([^",\r\n]+|"(?:[^"]|"")*")?</pre>
<p>Regex options: None<br>
Regex flavors: .NET,
        Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>( , | \r?\n | ^ )   # Capture the leading field delimiter to backref 1
(                   # Capture a single field to backref 2:
  [^",\r\n]+        #   Unquoted field
|                   #  Or:
  " (?:[^"]|"")* "  #   Quoted field (may contain escaped double quotes)
)?                  # The group is optional because fields may be empty</pre>
<p>Regex options: Free-spacing<br>
Regex flavors: .NET,
        Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<h4>Example web page with JavaScript</h4>
<pre>&lt;html&gt;
&lt;head&gt;
&lt;title&gt;Change CSV delimiters from commas to tabs&lt;/title&gt;
&lt;/head&gt;

&lt;body&gt;
&lt;p&gt;Input:&lt;/p&gt;
&lt;textarea id="input" rows="5" cols="75"&gt;&lt;/textarea&gt;

&lt;p&gt;&lt;input type="button" value="Replace" onclick="commasToTabs()"&gt;&lt;/p&gt;

&lt;p&gt;Output:&lt;/p&gt;
&lt;textarea id="output" rows="5" cols="75"&gt;&lt;/textarea&gt;

&lt;script&gt;
function commasToTabs() {
    var input  = document.getElementById("input"),
        output = document.getElementById("output"),
        regex  = /(,|\r?\n|^)([^",\r\n]+|"(?:[^"]|"")*")?/g,
        result = "",
        match;

    while (match = regex.exec(input.value)) {
        // Check the value of backreference 1
        if (match[1] == ",") {
            // Add a tab (in place of the matched comma) and backreference
            // 2 to the result. If backreference 2 is undefined (because
            // the optional, second capturing group did not participate in
            // the match), use an empty string instead.
            result += "\t" + (match[2] || "");
        } else {
            // Add the entire match to the result
            result += match[0];
        }

        // If there is an empty match, prevent some browsers from getting
        // stuck in an infinite loop
        if (match.index == regex.lastIndex) {
            regex.lastIndex++;
        }
    }

    output.value = result;
}
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;</pre>
<h2>9.12. Extract CSV Fields from a Specific Column</h2>
<h3>Solution</h3>
<pre>(,|\r?\n|^)([^",\r\n]+|"(?:[^"]|"")*")?</pre>
<p>Regex options: None<br>
Regex flavors: .NET,
        Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>( , | \r?\n | ^ )   # Capture the leading field delimiter to backref 1
(                   # Capture a single field to backref 2:
  [^",\r\n]+        #   Unquoted field
|                   #  Or:
  " (?:[^"]|"")* "  #   Quoted field (may contain escaped double quotes)
)?                  # The group is optional because fields may be empty</pre>
<p>Regex options: Free-spacing<br>
Regex flavors: .NET,
        Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<h4>Example web page with JavaScript</h4>
<pre>&lt;html&gt;
&lt;head&gt;
&lt;title&gt;Extract the third column from a CSV string&lt;/title&gt;
&lt;/head&gt;

&lt;body&gt;
&lt;p&gt;Input:&lt;/p&gt;
&lt;textarea id="input" rows="5" cols="75"&gt;&lt;/textarea&gt;

&lt;p&gt;&lt;input type="button" value="Extract Column 3"
    onclick="displayCsvColumn(2)"&gt;&lt;/p&gt;

&lt;p&gt;Output:&lt;/p&gt;
&lt;textarea id="output" rows="5" cols="75"&gt;&lt;/textarea&gt;

&lt;script&gt;
function displayCsvColumn(index) {
    var input = document.getElementById("input"),
        output = document.getElementById("output"),
        columnFields = getCsvColumn(input.value, index);

    if (columnFields.length &gt; 0) {
        // Show each record on its own line, separated by a line feed (\n)
        output.value = columnFields.join("\n");
    } else {
        output.value = "[No data found to extract]";
    }
}

// Return an array of CSV fields at the provided, zero-based index
function getCsvColumn(csv, index) {
    var regex = /(,|\r?\n|^)([^",\r\n]+|"(?:[^"]|"")*")?/g,
        result = [],
        columnIndex = 0,
        match;

    while (match = regex.exec(csv)) {
        // Check the value of backreference 1. If it's a comma,
        // increment columnIndex. Otherwise, reset it to zero.
        if (match[1] == ",") {
            columnIndex++;
        } else {
            columnIndex = 0;
        }
        if (columnIndex == index) {
            // Add the field (backref 2) at the end of the result array
            result.push(match[2]);
        }

        // If there is an empty match, prevent some browsers from getting
        // stuck in an infinite loop
        if (match.index == regex.lastIndex) {
            regex.lastIndex++;
        }
    }

    return result;
}
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;</pre>
<h3>Variations</h3>
<h4>Match a CSV record and capture the field in column 1 to
        backreference 1</h4>
<pre>^([^",\r\n]+|"(?:[^"]|"")*")?(?:,(?:[^",\r\n]+|"(?:[^"]|"")*")?)*</pre>
<p>Regex options: ^ and
          $ match at line breaks<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h4>Match a CSV record and capture the field in column 2 to
        backreference 1</h4>
<pre>^(?:[^",\r\n]+|"(?:[^"]|"")*")?,([^",\r\n]+|"(?:[^"]|"")*")?(?:,(?:[^",\r\n]+|"(?:[^"]|"")*")?)*</pre>
<p>Regex options: ^ and
          $ match at line breaks<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h4>Match a CSV record and capture the field in column 3 or higher
        to backreference 1</h4>
<pre>^(?:[^",\r\n]+|"(?:[^"]|"")*")?(?:,(?:[^",\r\n]+|"(?:[^"]|"")*")?){1},([^",\r\n]+|"(?:[^"]|"")*")?(?:,(?:[^",\r\n]+|"(?:[^"]|"")*")?)*</pre>
<p>Regex options: ^ and
          $ match at line breaks<br>
Regex flavors: .NET,
          Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h4>Replacement string</h4>
<pre>$1</pre>
<pre>\1</pre>
<h2>9.13. Match INI Section Headers</h2>
<h3>Solution</h3>
<pre>^\[[^\]\r\n]+]</pre>
<p>Regex options: ^ and $
        match at line breaks<br>
Regex flavors: .NET,
        Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h3>Variations</h3>
<pre>^\[Section1]</pre>
<p>Regex options: ^ and $
        match at line breaks<br>
Regex flavors: .NET,
        Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<h2>9.14. Match INI Section Blocks</h2>
<h3>Solution</h3>
<pre>^\[[^\]\r\n]+](?:\r?\n(?:[^[\r\n].*)?)*</pre>
<p>Regex options: ^ and $
        match at line breaks (“dot matches line breaks” must not be
        set)<br>
Regex flavors: .NET,
        Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>^ \[ [^\]\r\n]+ ]  # Match a section header
(?:                # Followed by the rest of the section:
  \r?\n            #   Match a line break character sequence
  (?:              #   After each line starts, match:
    [^[\r\n]       #     Any character except "[" or a line break character
    .*             #     Match the rest of the line
  )?               #   The group is optional to allow matching empty lines
)*                 # Continue until the end of the section</pre>
<p>Regex options: ^ and $
        match at line breaks, free-spacing (“dot matches line breaks” must not
        be set)<br>
Regex flavors: .NET,
        Java, XRegExp, PCRE, Perl, Python, Ruby</p>
<h3>Discussion</h3>
<pre>[Section1]
Item1=Value1
Item2=[Value2]

; [SectionA]
; The SectionA header has been commented out

ItemA=ValueA ; ItemA is not commented out, and is part of Section1

[Section2]
Item3=Value3
Item4 = Value4</pre>
<h2>9.15. Match INI Name-Value Pairs</h2>
<h3>Solution</h3>
<pre>^([^=;\r\n]+)=([^;\r\n]*)</pre>
<p>Regex options: ^ and $
        match at line breaks<br>
Regex flavors: .NET,
        Java, JavaScript, PCRE, Perl, Python, Ruby</p>
<pre>^               # Start of a line
( [^=;\r\n]+ )  # Capture the name to backreference 1
=               # Name-value delimiter
( [^;\r\n]* )   # Capture the value to backreference 2</pre>
<p>Regex options: ^ and $
        match at line breaks, free-spacing<br>
Regex flavors: .NET,
        Java, XRegExp, PCRE, Perl, Python, Ruby</p>

</body></html>