C# substring extensions inspired by XPath's substring-before and substring-after functions.

SubstringExtensions

public static class SubstringExtensions {
    /// <summary>
	/// Gets the substring after the first occurence of the specified character.
	/// </summary>
	/// <param name="self">The string self.</param>
	/// <param name="ch">The character.</param>
	/// <returns>The substring after the first occurrence of the specified character. If
	/// The character does not occur in the string, the empty string is returned.</returns>
	public static string SubstringAfter(this string self, char ch) {
		int index = self == null ? -1 : self.IndexOf(ch);
		return index > -1 ? self.Substring(index + 1) : string.Empty;
	}
	/// <summary>
	/// Gets the substring after the first occurence of the specified string.
	/// </summary>
	/// <param name="self">The string self.</param>
	/// <param name="str">The string to find.</param>
	/// <returns>The substring after the first occurrence of the specified string. If
	/// The string does not occur in the self, the empty string is returned.</returns>
	public static string SubstringAfter(this string self, string str) {
		int index = self.IndexOf(str);
		if (index > -1) {
			return self.Substring(index + str.Length);
		}
		return string.Empty;
	}
	/// <summary>
	/// Gets the substring before the first occurrence of a character
	/// </summary>
	/// <param name="self">The self <see cref="string"/></param>
	/// <param name="ch">The character</param>
	/// <returns>The substring before the first occurrence of the specified character. If
	/// The character does not occur in the self, the empty string is returned.</returns>
	public static string SubstringBefore(this string self, char ch) {
		int index = self.IndexOf(ch);
		if (index > -1) {
			return self.Substring(0, index);
		}
		return string.Empty;
	}
	/// <summary>
	/// Gets the substring before the first occurrence of a string.
	/// </summary>
	/// <param name="self">The self <see cref="string"/></param>
	/// <param name="str">The string to look for.</param>
	/// <returns>The substring before the first occurrence of the specified string. If
	/// The string does not occur in the self, the empty string is returned.</returns>
	public static string SubstringBefore(this string self, string str) {
		int index = self.IndexOf(str);
		if (index > -1) {
			return self.Substring(0, index);
		}
		return string.Empty;
	}
	/// <summary>
	/// Gets the substring after the last occurrence of a character.
	/// </summary>
	/// <param name="self">The self <see cref="string"/></param>
	/// <param name="ch">The character.</param>
	/// <returns>The substring after the last occurrence of the specified character. If
	/// The character does not occur in the self, the empty string is returned.</returns>
	public static string SubstringAfterLast(this string self, char ch) {
		int index = self.LastIndexOf(ch);
		if (index > -1) {
			return self.Substring(index + 1);
		}
		return string.Empty;
	}
	/// <summary>
	/// Gets the substring after the last occurrence of a string.
	/// </summary>
	/// <param name="self">The self <see cref="string"/></param>
	/// <param name="str">The string.</param>
	/// <returns>The substring after the last occurrence of the specified string. If
	/// The string does not occur in the self, the empty string is returned.</returns>
	public static string SubstringAfterLast(this string self, string str) {
		int index = self.LastIndexOf(str);
		if (index > -1) {
			return self.Substring(index + str.Length);
		}
		return string.Empty;
	}
	/// <summary>
	/// Gets the substring before the last occurrence of a character.
	/// </summary>
	/// <param name="self">The self <see cref="string"/></param>
	/// <param name="ch">The character.</param>
	/// <returns>The substring before the last occurrence of the specified character. If
	/// The character does not occur in the self, the empty string is returned.</returns>
	public static string SubstringBeforeLast(this string self, char ch) {
		int index = self.LastIndexOf(ch);
		if (index > -1) {
			return self.Substring(0, index);
		}
		return string.Empty;
	}
	/// <summary>
	/// Gets the substring before the last occurrence of a string.
	/// </summary>
	/// <param name="self">The <see cref="string"/> self.</param>
	/// <param name="str">The string.</param>
	/// <returns>The substring after the last occurrence of the specified string. If
	/// The string does not occur in the self, the empty string is returned.</returns>
	public static string SubstringBeforeLast(this string self, string str) {
		int index = self.LastIndexOf(str);
		if (index > -1) {
			return self.Substring(0, index);
		}
		return string.Empty;
	}
}