Errata

JavaScript does not support conditionals.

In the Solution section, remove JavaScript from the first list of regex flavors (but leave it in the second list). Change "Java and Ruby" and "Java or Ruby" to "Java, JavaScript, and Ruby" and "Java, JavaScript, or Ruby".

In the Discussion section, remove JavaScript from the first paragraph.

Page 454, first regex:

Change:

^(?:[^>"']|"[^"]*"|'[^']*')+?\sclass\s*=\s*("[^"]*"|'[^']*')

To:

^(?:[^>"']|"[^"]*"|'[^']*')+?\sclass\s*=\s*(?:"([^"]*)"|'([^']*)')

Page 454, second paragraph:

Change:

This captures the entire class value and its surrounding quote marks to backreference 1.

To:

This captures the entire class value to backreference 1 or 2, depending on the type of quote marks surrounding the value.

Page 454, fourth paragraph:

Change:

Finally, if both of the previous regexes matched successfully, you?ll want to search within backreference 1 of the second regex?s matches using the following pattern:

To:

Finally, if both of the previous regexes matched successfully, you?ll want to search within backreferences 1 and 2 of the second regex?s matches using the following pattern:

Note from the Author or Editor:
I got this submission backwards--I included the fix in the description, and have the details here. The error is that the previous version of the regex in question included the surrounding quote marks in the backreference, but the followup regex to search within the backreference for a class did not account for the quote marks.

On page 65 your 2nd and 3rd examples would incorrectly match input
that was not in the form of a hexadecimal number.
For example, the input 9g01h would, incorrectly, succeed in making a
match.
The regex should be \b[a-fA-F0-9]{1,8}h?\b

Note from the Author or Editor:
In the Solution section, change both instances of [a-z0-9] to [a-f0-9]

Also, change the second "Hexadecimal number" subheading to "Hexadecimal number with optional suffix" to differentiate it from the first.

"=~ variable" should be replaced with "$~ variable"

Some Unicode propties are missing from the list, these may include <\p{Lu}>, <\p{L&}>, <\p{Lm}>, and <\p{Mc}>.

Note from the Author or Editor:
In the "Unicode property or category" list beginning on page 45, the following 3 items should be added:
Insert between \p{Ll} and \p{Lt}:
\p{Lu}
An uppercase letter that has a lowercase variant
Insert between \p{Lt} and \p{Lo}:
\p{Lm}
A special character that is used as a letter
Insert between \p{Mn} and \p{Me}:
\p{Mc}
A character intended to be combined with another character that takes up extra space (vowel signs in many Eastern scripts)

In JavaScript, string.match(/regexp/) works identically to /regexp/.exec(string). string.match only differs when provided a regex that uses /g.

Printed:
This problem does not exist with string.match() (Recipe 3.10) or string.replace() (Recipe 3.14).

Corrected:
This problem does not exist with string.replace() (Recipe 3.14) or when finding all matches with string.match() (Recipe 3.10).

The following regular expressions all include the character class [\s\S] and are listed as JavaScript-only, although they in fact work with all regex flavors covered by the book. The intention was to suggest that they should only be used in JavaScript, because more appropriate alternatives are already listed for other regex flavors. Thus, whether what's currently printed is actually wrong is debatable, but to avoid confusion it is better to expand the regex flavor lists referenced below. Some related text changes are also listed.

Page 34:
----------
Printed:
Regex flavor: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 35:
----------
Printed (3rd paragraph):
'.' thus matches any single character except a newline character.

Corrected:
. thus matches any single character except a newline character.

Page 245:
----------
Printed:
Regex flavor: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 246 (two fixes):
----------
Printed (1st paragraph):
In this case, the pattern .* (or [\S\s]* in the JavaScript version) is used to simply match the entire subject text with no added constraints.

Corrected:
In this case, the pattern .* (or [\S\s]* in the version that adds JavaScript support) is used to simply match the entire subject text with no added constraints.

Printed (2nd paragraph):
This regex uses the dot matches line breaks option to allow the dots to match all characters, including line breaks. See Recipe 3.4 for details about how to apply this modifier with your programming language. The JavaScript regex is different, since JavaScript does not have a dot matches line breaks option. See Any character including line breaks on page 35 in Recipe 2.4 for more information.

Corrected:
The first regex uses the dot matches line breaks option so that it will work correctly when your subject string contains line breaks. See Recipe 3.4 for details about how to apply this modifier with your programming language. JavaScript doesn't have a dot matches line breaks option, so the second regex uses a character class that matches any character. See Any character including line breaks on page 35 in Recipe 2.4 for more information.

Page 306:
----------
Printed:
Regex flavor: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 309 x 2 (two occurrences, both with the same corrected replacement):
----------
Printed:
Regex options: ^ and $ match at line breaks
Regex flavor: JavaScript

Corrected:
Regex options: ^ and $ match at line breaks ("dot matches line breaks" must not be set)
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 429:
----------
Printed:
Regex flavors: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 430:
----------
Printed:
Regex flavors: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 458:
----------
Printed:
Regex flavor: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 460:
----------
Printed:
Regex flavor: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Page 463 x 2 (two occurrences, both with the same corrected replacement):
----------
Printed:
Regex flavor: JavaScript

Corrected:
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

The \b at the start of the regular expression under "floating point number" should be deleted. It prevents the regular expression from matching floating point numbers without an integer part, as is required by the problem statement for this recipe.

Note from the Author or Editor:
Delete \b at the start of the regular expression under "floating point number"

There is a mistake in the description of the Discover card format. However, the included regexes are correct.

----------
Printed:
Discover
16 digits, starting with 6011, or 15 digits starting with 5.

Corrected:
Discover
16 digits, starting with 6011 or 65.
----------

The numbers 6011 and 65 should use a fixed-width font. The number 16 at the beginning of the corrected sentence should not.

-- Reported by Vikas Shukla at http://referencedesigner.com/blog/?p=328.

as published:
"you want to extract jan from http://jan@www.regexcookbook.com"

According to RFC1738, usernames are not allowed in the http scheme. A better example would be to use the ftp scheme, which does allow the username:password component in a URL.

Note from the Author or Editor:
Change http://jan@www.regexcookbook.com into ftp://jan@www.regexcookbook.com

as published:
"<(\d\d){3}> matches a string of two, four or six digits."
corrected:
"<(\d\d){3}> matches a string of six digits."

Note from the Author or Editor:
In the first paragraph on page 67, change {3} into {1,3}
In the second paragraph, do NOT change the first occurrence of {3} at the start of the paragraph. Change the 2nd and 3rd occurrrences of {3} in the second paragraph into {1,3}

lines = re.split("\r?\n", subject)

reobj = re.compile("regex pattern")
for line in lines:
if re.search(line):
# the regex matches line
else:
# the regex does not match line


This is the corrected version.
The object returned from re.compile() should be used to call search()

lines = re.split("\r?\n", subject)

reobj = re.compile("regex pattern")
for line in lines:
if reobj.search(line):
# the regex matches line
else:
# the regex does not match line

Note from the Author or Editor:
In the Python section on page 210, this line:

if re.search(line):

must be changed into:

if reobj.search(line):

Solution
\a\e\f\n\r\t\v
Regex options: None
Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby
\x07\x1B\f\n\r\t\v
Regex options: None
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Perl does not support the \v vertical tab escape sequence. It must be represented in Perl using a hexadecimal (\x0B) or octal (\013) escape sequence instead.

Note from the Author or Editor:
On page 28, in the Solution section, remove Perl from the list of regex flavors for both given solutions. Add a 3rd solution:

\a\e\f\n\r\t\0x0B
Regex options: None
Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby

On page 29, append this sentence to the first paragraph (which starts with "The ECMA-262 standard..."):

Perl does not support \v, so we have to use a different syntax for the vertical tab in Perl.

In this sentence, \v should be formatted as a regular expression, just as \a and \e are in that sentence.