Regular Expressions Cookbook

2.2. Match Nonprintable Characters

Problem

Match a string of the following ASCII control characters: bell, escape, form feed, line feed, carriage return, horizontal tab, vertical tab. These characters have the hexadecimal ASCII codes 07, 1B, 0C, 0A, 0D, 09, 0B.

Solution

\a\e\f\n\r\t\v

Regex options: None

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

\x07\x1B\f\n\r\t\v

Regex options: None

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

\a\e\f\n\r\t\0x0B

Regex options: None

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

Discussion

Seven of the most commonly used ASCII control characters have dedicated escape sequences. These all consist of a backslash followed by a letter. This is the same syntax that is used for string literals in many programming languages. Table 2-1 shows the common nonprinting characters and how they are represented.

Table 2-1. Nonprinting characters

Representation	Meaning	Hexadecimal representation
‹\a›	bell	0x07
‹\e›	escape	0x1B
‹\f›	form feed	0x0C
‹\n›	line feed (newline)	0x0A
‹\r›	carriage return	0x0D
‹\t›	horizontal tab	0x09
‹\v›	vertical tab	0x0B

Perl does not support \v, so we have to use a different syntax for the vertical tab in Perl. The ECMA-262 standard does not support ‹\a› and ‹\e›. Therefore, we use a different syntax for the JavaScript examples in this book, even though many browsers do support ‹\a› and ‹\e›.

These control characters, as well as the alternative syntax shown in the following section, can be used equally inside and outside character classes in your regular ...