A-154
Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide
OL-28417-02
Chapter Understanding Regular Expressions, Special Characters, and Patterns
Special Characters
Special Characters
Certain keyboard characters have special meaning when used in regular expressions. Table 37 lists the
keyboard characters that have special meaning.
To use these special characters as single-character patterns, remove the special meaning by preceding
each character with a double backslash (\\). In the following examples, single-character patterns
matching a dollar sign, an underscore, and a plus sign, respectively, are shown.
\\$ \\_ \\+
Character Pattern Ranges
A range of single-character patterns can be used to match command output. To specify a range of
single-character patterns, enclose the single-character patterns in square brackets ([ ]). Only one of these
characters must exist in the string for pattern-matching to succeed. For example, [aeiou] matches any
one of the five vowels of the lowercase alphabet, while [abcdABCD] matches any one of the first four
letters of the lowercase or uppercase alphabet.
You can simplify a range of characters by entering only the endpoints of the range separated by a dash
(–), as in the following example:
[a–dA–D]
To add a dash as a single-character pattern in the search range, precede it with a double backslash:
[a–dA–D\\–]
A bracket (]) can also be included as a single-character pattern in the range:
[a–dA–D\\–\\]]
Invert the matching of the range by including a caret (^) at the start of the range. The following example
matches any letter except the ones listed:
[^a–dqsv]
The following example matches anything except a right square bracket (]) or the letter d:
[^\\]d]
Ta b l e 37 Characters with Special Meaning
Character Special Meaning
. Matches any single character, including white space.
* Matches 0 or more sequences of the pattern.
+ Matches 1 or more sequences of the pattern.
? Matches 0 or 1 occurrences of the pattern.
^ Matches the beginning of the string.
$ Matches the end of the string.
_ (underscore) Matches a comma (,), left brace ({), right brace (}), the beginning of the string,
the end of the string, or a space.
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