NR-grep: a fast and flexible pattern-matching tool

We present nrgrep (\nondeterministic reverse grep"), a new pattern matching tool designed for eecient search of complex patterns. Unlike previous tools of the grep family, such as agrep and Gnu grep, nrgrep is based on a single and uniform concept: the bit-parallel simulation of a nondeterministic suux automaton. As a result, nrgrep can nd from simple patterns to regular expressions, exactly or allowing errors in the matches, with an eeciency that degrades smoothly as the complexity of the searched pattern increases. Another concept fully integrated into nrgrep and that contributes to this smoothness is the selection of adequate subpatterns for fast scanning, which is also absent in many current tools. We show that the eeciency of nrgrep is similar to that of the fastest existing string matching tools for the simplest patterns, and by far unpaired for more complex patterns.