We can also search for something at the end of a file. According to the Vim help files, it is often easier to use the first occurrence of a word in a file: Match (with zero length) when the previous atom doesn't match.For example, if we want to find all the lines not containing the word 'foo', is an example: When examining a log file, you might only be interested in lines not containing the word "Warning", so the search command match all words except 'foo', \\) The atom 'Foo' followed by end-of-word Searching with / will find everything but the regular expression you have specified. When first attempting this problem, most people consider the regular expression: /. matches the characters chocolate literally (case sensitive). I found that it was difficult to write a regular expression that would find C style comments (the comments that start with / and end with /) because my text editor does not implement the 'non-greedy matching' feature of regular expressions. matches any character (except for line terminators) matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy) chocolate. You are now editing a clone of your original file with all lines not matching "warning" removed and you can edit it at will. Assert that the Regex below does not match. Therefore, the regex engine goes back from the end of the string to find the quote (). However, it already reaches the end of the string.
In contrast, Perl, PCRE, Python, Ruby, Java, and many other languages have regular expression implementations based on recursive backtracking that are simple but can be excruciatingly slow. So the difference between the greedy and the non-greedy match is the following: The greedy match will try to match as many repetitions of the quantified pattern.
The traditional approach to find lines not matching a pattern is using the :v command:Ī neat trick when working with a large log file where you want to filter out as many irrelevant lines as possible before you get started on your real search is to save the file under a temporary name and delete all non-matching lines there: The regex engine examines the last rule in the pattern, which is a quote (). Regular expression matching can be simple and fast, using finite automata-based techniques that have been known for decades.