Search more efficiently with ugrep

Tutorial – ugrep

Article from Issue 245/2021

Searching for text in files or data streams is a common and important function. Ugrep tackles this task quickly, efficiently, and even interactively if needed.

Grep is one of the oldest Unix commands. The abbreviation "grep" stands for Global/Regular Expression/Print or Global search for a Regular Expression and Print out matched lines. It picks up on the syntax of the original Unix editor, QED, which used g/re/p to search for patterns in text files. In addition to fixed search terms, it can also search for patterns with wildcard characters. The GNU variant of grep is normally installed on Linux. It extends the features of the original grep in some places, for example, allowing recursive searching in directories.

Another variant of grep, agrep (approximate grep) [1], extends text searching to include fuzzy searches. It also finds near misses as long as the differences are below a specified threshold, known as the word distance. This is calculated from the necessary permutations, deletions, and additions of letters that convert the search pattern into the actual data.

In addition, there are some variants of grep that also find search patterns in certain archive types, such as ZIP files. These programs are relatively slow, since they first need to unpack the archive. However, all grep variants used on Linux can also read data from pipes via the standard input channel and write the results to the standard output channel for searching in archives (Listing 1).


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