Reference: Regular Expressions
A regular expression is a formula composed of characters and operators that represent a specific pattern. This formula is used to locate text strings that match this pattern.
A simple example is searching your computer for a list of all the files that have the .txt extension. To do this, you use the substitution formula *.txt where * represents any alphanumeric characters A-Z or 0-9. Similarly, regular expressions allow you to create a formula that represents the text pattern to search for.
Regular expressions can be simple or very complex. For example, you can write expressions to search for any of the following:
- Specific sequence of characters
- Specific format such as (999)999-9999 to find phone numbers
- Special characters such as spaces or tabs
- Repeated words (or any text string)
- One text string always followed by another text string
By using operators in your expression, you can find text that matches a pattern or text that does NOT match the pattern.
Sample Regular Expressions
Regular expressions can be used in several commands. There are samples for these commands that you can copy-and-paste, and then edit as needed.
- Samples for the Import Format Editor command
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Samples for the Advanced Select command |
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| Selection criteria
(for object character strings such as names, point IDs, and feature codes) |
Expression
(not case-sensitive) |
Example |
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Select objects with a specific character in any position. |
Enter a, where "a" is the character used in the search. (Equivalent to *a* wildcard search.) |
a will select apple, cat, and era. |
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Select objects with a specific character in the first position. |
Enter ^a, where "a" is the character used in the search. (Equivalent to a* wildcard search.) |
^1 will select 1, 15, and 129F. |
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Select objects with a specific character in the second position. |
Enter ^.a, where "a" is the character used in the search. |
^.b will select aba, 1b2, and ab2 |
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Select objects with a specific character in the third (or more) position. |
Enter ^..a, where "a" is the character used in the search. (Additional periods can be added to specify further positions in the string.) |
^..n will select control and b2new |
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Select objects with a specific character in the last position. |
Enter a$, where "a" is the character used in the search. (Equivalent to *a wildcard search.) |
s$ will select 205 s and cas |
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Select objects starting and ending with specific characters |
Enter ^a.*b$, where "a" and "b" are the characters used in the search. |
^p.*s$ will select pipes and points. |
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Select objects with one specific name (or part of a name) or another. |
Enter ab|cd, where "ab" and "cd" are the names used in the search. |
bush|shrub will select all objects (feature codes, for example) with bush or shrub as all or part of their names. |
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Select objects numerically or alphabetically ranging from one number or letter to another |
Enter ^[a-d], where "a" and "d" are the characters that define the range used in the search. |
^[2-5] will select 2, 3, and 5. |
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Select objects that include a decimal point or comma. |
Enter \. or \,. |
\. will select 1.0 and 0.025 |
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Select objects that start with either of two specific characters |
Enter ^[ab], where "a" and "b" are the character used in the search. |
^[89] will select 8, 82, and 919 |
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Select objects numerically or alphabetically ranging from one number or letter to more than one choice of number or letter repeated a specified number of times. |
Enter [a-d]{x}, where "a" and "d" are the characters that define the range used in the search and “x” is the multiplier. |
[1-9]{4} will select 1111, 3333, and 9999. |
More information
For more short examples, see:
http://www.regular-expressions.info/reference.html.
Syntax details are located at:
http://en.wikipedia.org/wiki/Regular_expression
For a quick tutorial on regular expressions, visit:
https://www.codeproject.com/Articles/9099/The-30-Minute-Regex-Tutorial
