Regular Expressions Cookbook, 2nd Edition

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.

This demonstrates the use of escape sequences and how to reference characters by their hexadecimal codes.

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, Python, Ruby

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

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 by 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	Regex flavors
‹\a›	bell	0x07	.NET, Java, PCRE, Perl, Python, Ruby
‹\e›	escape	0x1B	.NET, Java, PCRE, Perl, Ruby
‹\f›	form feed	0x0C	.NET, Java, JavaScript, PCRE, Perl, Python, Ruby
‹\n›	line feed (newline)	0x0A	.NET, Java, JavaScript, PCRE, Perl, Python, Ruby
‹\r›	carriage return	0x0D	.NET, Java, JavaScript, PCRE, Perl, Python, Ruby
‹\t›	horizontal tab	0x09	.NET, Java, JavaScript, PCRE, Perl, Python, Ruby
‹\v›	vertical tab	0x0B	.NET, Java, JavaScript, Python, Ruby

In Perl 5.10 and later, ...