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 |
---|---|---|
‹ | bell | 0x07 |
‹ | escape | 0x1B |
‹ | form feed | 0x0C |
‹ | line feed (newline) | 0x0A |
‹ | carriage return | 0x0D |
‹ | horizontal tab | 0x09 |
‹ | 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 ‹
› and
‹\a
›. Therefore, we use a different
syntax for the JavaScript examples in this book, even though many
browsers do support ‹\e
\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 ...
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