Regular Expressions Cookbook

8.2. Replace <b> Tags with <strong>

Problem

You want to replace all opening and closing <b> tags in a string with corresponding <strong> tags, while preserving any existing attributes.

Solution

This regex matches opening and closing <b> tags, with or without attributes:

<(/?)b\b((?:[^>"']|"[^"]*"|'[^']*')*)>

Regex options: Case insensitive

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

In free-spacing mode:

<                #
(/?)             # Capture the optional leading slash to backreference 1
b \b             # Complete tag name, with word boundary
(                # Capture any attributes, etc. to backreference 2
    (?: [^>"']   #     Any character except >, ", or '
      | "[^"]*"  #     Double-quoted attribute value
      | '[^']*'  #     Single-quoted attribute value
    )*           #
)                #
>                #

Regex options: Case insensitive, free-spacing

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

To preserve all attributes while changing the tag name, use the following replacement text:

<$1strong$2>

Replacement text flavors: .NET, Java, JavaScript, Perl, PHP

<\1strong\2>

Replacement text flavors: Python, Ruby

If you want to discard any attributes in the same process, omit backreference 2 in the replacement string:

<$1strong>

Replacement text flavors: .NET, Java, JavaScript, Perl, PHP

<\1strong>

Replacement text flavors: Python, Ruby

Recipe 3.15 shows the code needed to implement this.

Discussion

The previous recipe included a detailed discussion of many ways to match any XML-style tag. That frees this recipe to focus on a straightforward approach to search for a specific type of ...