Regular Expressions
Regular expressions (regex) is a highly descriptive language commonly used to search through a set of data. There are different variants of regex but most share a similar syntax.
This section describes regex in the context of PSM. PSM allows you to use regular expressions to control how entries in the Network tree are categorized.
A regular expression is created using one or more constructs. The expression is then compared against a set of data, which, in the case of a branch in the Network tree, is the set of entries or names in that branch. The simplest way to envision this is to imagine a scanner that scans through the set of names one character at a time looking for matches to the given expression.1
 | Note: 1 In reality, the regex engine uses algorithmic methods to look for matches. |
Table 1: Common Regex Constructs
Construct | Description | Example |
|---|---|---|
Characters and character classes | ||
char | Literal. Matches if the specified char matches the character at the current position in the data set. | a matches abc |
. (dot) | Wildcard. Matches any single character at the current position in the data set. Does not match if there is no character at the current position (e.g. at the end of a name). | ab.d matches abcd and abdd |
[chars] | Character class. Matches if any single char within the square parentheses matches the character at the current position in the data set. The characters in the parentheses can be a list of characters or a range of characters, or a negation. | [a] matches abc [abc] matches abc, abc, and abc [a-zA-Z] matches any lowercase or uppercase letter [^a0-9] matches any character that is not an a or a digit |
\w | Word character, shorthand for [a-zA-Z0-9_]. | \w matches !@#-a-%$# |
\d | Digit character, shorthand for [0-9]. | \d matches abc2def |
\ (backslash) | Escape character. When immediately preceding one of the following special characters, [\^$.|?*+(){} outside a character class, the \ suppresses the special character's meaning, and the special character is treated as a literal. When immediately preceding one of the following special characters, ^-]\ inside a character class, the \ suppresses the special character's meaning, and the special character is treated as a literal. | \.com outside a character class matches mycompany.com |
Construct | Description | Example |
|---|---|---|
Anchors | ||
^ (caret) | Match at the start of the string or after a newline.1 Note: A starting ^ inside a character class is a negation. Note: 1Each name in the branch is separated by the newline character. | If the string is network_subnet, then: ^net matches network_subnet |
$ (dollar) | Match at the end of the string or before a newline. | If the string is network_subnet, then: net$ matches network_subnet |
Construct | Description | Example |
|---|---|---|
Quantification | ||
* (asterisk) | Match the preceding item 0 or more times, as many times as possible (greedy match). | om* matches optical om* matches commissioning |
+ | Match the preceding item 1 or more times, as many times as possible (greedy match). | om+ matches commissioning |
? | Match the preceding item 0 or 1 time, as many times as possible (greedy match). | om? matches optical om? matches commissioning |
Construct | Description | Example |
|---|---|---|
Groupings | ||
(expression1|expression2|...) | Alternation. Matches if any of the expressions matches. | (aaa|bbb) matches aaa or bbb |
(?<=lb_expression)expression | Lookbehind. Matches if the main expression and the preceding lookbehind expression match. The part of the match due to lb_expression is not included in the matched result. The matched result consists of the match resulting from expression only. This is useful when you want to search for a string and you want to exclude the first part of that string from the matched result itself. | (?<=www.)\w*\.com matches www.mycompany.com The resulting matched string is mycompany.com. |
expression(?=la_expression) | Lookahead. Matches if the main expression and the following lookahead expression match. The part of the match due to la_expression is not included in the matched result. The matched result consists of the match resulting from expression only. This is useful when you want to search for a string and you want to exclude the latter part of that string from the matched result itself. | \w*(?=@) matches john@mycompany.com The resulting matched string is john. |
