August 2012
Intermediate to advanced
609 pages
19h 16m
English
Content preview from Regular Expressions Cookbook, 2nd Edition
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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 |
|---|---|---|---|
‹ | bell | 0x07 | .NET, Java, PCRE, Perl, Python, Ruby |
‹ | escape | 0x1B | .NET, Java, PCRE, Perl, Ruby |
‹ | form feed | 0x0C | .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
‹ | line feed (newline) | 0x0A | .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
‹ | carriage return | 0x0D | .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
‹ | horizontal tab | 0x09 | .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
‹ | vertical tab | 0x0B | .NET, Java, JavaScript, Python, Ruby |
In Perl 5.10 and later, ...
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