Open Source Research and Development

How to search for lines that don’t contain a particular pattern is fairly easy in some programs, obscure in others, and almost impossible yet in others. That is, assuming your program of choice supports regular expressions. I review how to achieve this functionality in Perl, Vim, grep, and vi.
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Overview
The UNIX grep utility marked the birth of a global regular expression print (GREP) tools. Searching for patterns in text is important operation in a number of domains, including program comprehension and software maintenance, structured text databases, indexing file systems, and searching natural language texts. Such a wide range of uses inspired the development of variations of the original UNIX grep. These variations range from adding new features, to employing faster algorithms, to changing the behaviour of pattern matching and printing.
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