You can use * with expressions, not just characters. When used in a regular expression, this multiplier means match zero or more of the previous expression. One of the more common multipliers used is the asterisk, or star character (*). Multipliers apply to the previous character in the regular expression. Multipliers are a mechanism used often with wildcards. Changing the regular expression to ct matches patterns that start with a c, followed by either an a, o, or u, followed by a t.
To match specific characters, replace the unrestricted wildcard with acceptable characters. Using an unrestricted wildcard you cannot predict the character that would match the wildcard. Example matches include cat, concatenate, vindication, c5t, and c$t. A regular expression of c.t searches for a string that contains a c followed by any single character followed by a t. Regular expressions use a period or dot (.) to match any single character with the exception of the newline character. For example, to locate the word cat when it is the only word on a line, use ^cat$.Īdding Wildcards and Multipliers to Regular Expressions To locate the only word on a line, use both the beginning and end-of-line anchors. Applying dog$ to the file would find two matches: dog To locate lines in the file ending with dog, use that exact expression and an end of line anchor to create the regular expression dog$. The $cat regular expression would not find any matching words. Using the same file as above, the ^cat regular expression would match two words. To search at the end of a line, use the dollar sign ($). To search at the beginning of a line, use the caret character (^). Use a line anchor to control the location of where the regular expression looks for a match. Note that the regular expression would match the search string no matter where on the line it occurred: the beginning, end, or middle of the word or line. The previous section used an exact match regular expression on a file. Using cat as the regular expression to search the previous file returns the following matches: cat Suppose a user is looking through the following file looking for all occurrences of the pattern cat: catĬat is an exact match of a c, followed by an a, followed by a t with no other characters in between. An exact match is when the characters in the regular expression match the type and order in the data that is being searched. The simplest regular expression is an exact match. This section looks at the syntax used when creating regular expressions, as well as showing some regular expression examples Describing a Simple Regular Expression Regular expressions are a language of their own, which means they have their own syntax and rules. Programming languages such as Perl, Python, and C can all use regular expressions when using pattern matching criteria. The vim, grep, and less commands can all use regular expressions. Regular expressions provide a pattern matching mechanism that facilitates finding specific content.
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