Alfred Vaino Aho (born August 9, 1941) is a Canadian computer scientist best known for his work on programming languages, compilers, and related algorithms, and his textbooks on the art and science of computer programming.  
Aho was elected into the
National Academy of Engineering in 1999 for his contributions to the fields of algorithms and programming tools.
He and his long-time collaborator
Jeffrey Ullman are the recipients of the 2020 Turing Award, generally recognized as the highest distinction in computer science.
Aho received a B.A.Sc. (1963) in Engineering Physics from the
University of Toronto, then an M.A. (1965) and Ph.D. (1967) in Electrical Engineering/Computer Science from Princeton University. He conducted research at  Bell Labs from 1967 to 1991, and again from 1997 to 2002 as Vice President of the Computing Sciences Research Center. Since 1995, he has held the Lawrence Gussman Professorship in  Computer Science at Columbia University. He served as chair of the department from 1995 to 1997, and again in the spring of 2003.
In his PhD thesis Aho created
indexed grammars and the  nested-stack automaton as vehicles for extending the power of  context-free languages, but retaining many of their decidability and closure properties. One application of indexed grammars is modelling parallel rewriting systems, particularly in biological applications. 
After graduating from Princeton, Aho joined the Computing Sciences Research Center at Bell Labs where he devised efficient
regular expression and string-pattern matching algorithms that he implemented in the first versions of the Unix tools
fgrep algorithm has become known as the
Aho-Corasick algorithm; it is used by several bibliographic search-systems, including the one developed by Margaret J. Corasick, and by other string-searching applications.
At Bell Labs, Aho worked closely with
Steve Johnson and Jeffrey Ullman to develop efficient algorithms for analyzing and translating programming languages. Steve Johnson used the bottom-up LALR parsing algorithms to create the syntax-analyzer generator  yacc, and  Michael E. Lesk and Eric Schmidt used Aho's regular-expression pattern-matching algorithms to create the lexical-analyzer generator lex. The lex and yacc tools and their derivatives have been used to develop the front ends of many of today's programming language compilers. 
Aho and Ullman wrote a series of textbooks on compiling techniques that codified the theory relevant to compiler design. Their 1977 textbook
had a green dragon on the front cover and became known as "the green dragon book". In 1986 Aho and Ullman were joined by Principles of Compiler Design Ravi Sethi to create a new edition, "the red dragon book" (which was briefly shown in the 1995 movie ), and in 2006 also by Hackers Monica Lam to create "the purple dragon book". The dragon books are used for university courses as well as industry references.
In 1974, Aho,
John Hopcroft, and Ullman wrote the Design and Analysis of Computer Algorithms, codifying some of their early research on algorithms. This book became one of the most highly cited books in computer science for several decades and helped to stimulate the creation of algorithms and data structures as a central course in the computer science curriculum.
Aho is also widely known for his co-authorship of the
AWK programming language with Peter J. Weinberger and Brian Kernighan (the "A" stands for "Aho"). As of 2010 Aho's research interests include programming languages, compilers, algorithms, and  quantum computing. He is part of the Language and Compilers research-group at Columbia University.
Overall, his works have been cited 81,040 times and he has an
h-index of 66, as of May 8, 2019.
Aho has received many prestigious honors, including the
IEEE's John von Neumann Medal and membership in the National Academy of Engineering. He was elected a Fellow of the American Academy of Arts and Sciences in 2003. He holds honorary doctorates from the  University of Waterloo, from the  University of Helsinki, and from the  University of Toronto. He is a Fellow of the  American Association for the Advancement of Science, ACM, Bell Labs, and IEEE.
Aho has twice served as chair of the Advisory Committee for the Computer and Information Science and Engineering Directorate of the National Science Foundation. He is a past president of the
ACM Special Interest Group on Algorithms and Computability Theory. Aho, Hopcroft, and Ullman were co-recipients of the 2017  C&C Prize awarded by NEC Corporation. He and Ullman were named recipients of 2020  Turing Award on March 31, 2021.
Aho has taught at Columbia University in New York City since 1995. He won the Great Teacher Award from the Society of Columbia Graduates in 2003.
A. V. Aho and
J. D. Ullman, The Theory of Parsing, Translation, and Compiling, Vol. 1, Parsing. Prentice Hall, 1972. ISBN 0-13-914556-7 A. V. Aho (ed.)
Currents in the Theory of Computing. Prentice Hall, 1973. ISBN 0-13-195651-5  A. V. Aho and
J. D. Ullman, The Theory of Parsing, Translation, and Compiling, Vol. 2, Compiling. Prentice-Hall, 1973. ISBN 978-0-13-914564-3 A. V. Aho,
J. E. Hopcroft, J. D. Ullman, The Design and Analysis of Computer Algorithms. Addison-Wesley, 1974. ISBN 0-201-00023-7 A. V. Aho and
J. D. Ullman, Principles of Compiler Design. Addison-Wesley, 1977. ISBN 0-201-00022-9 A. V. Aho,
J. E. Hopcroft, J. D. Ullman, Data Structures and Algorithms. Addison-Wesley, 1983. ISBN 0-201-00023-7 A. V. Aho,
R. Sethi, J. D. Ullman, Addison-Wesley, Reading MA 1986. Compilers: Principles, Techniques, and Tools. ISBN 0-201-10088-6 A. V. Aho,
B. W. Kernighan, and P. J. Weinberger, The AWK Programming Language. Addison-Wesley, 1988. ISBN 978-0-201-07981-4 A. V. Aho and
J. D. Ullman, W. H. Freeman/Computer Science Press, 1992. Foundations of Computer Science. ISBN 978-0-7167-8233-9 
 A. V. Aho, M. S. Lam, R. Sethi, and J. D. Ullman, Addison-Wesley, 2007. Compilers: Principles, Techniques, and Tools, Second Edition. ISBN 978-0-321-48681-3
Alfred Vaino Aho at the Mathematics Genealogy Project
Aho, A.; Gottlob, G. (2014). "A front row seat to Communications' editorial transformation". Communications of the ACM. 57 (4): 5. doi: 10.1145/2582611. S2CID 21553189.
Aho, A.V. (1990). "Algorithms for Finding Patterns in Strings". Handbook of Theoretical Computer Science. MIT Press. pp. 255-300.
Computerworld Interview with Alfred V. Aho
Archived May 29, 2008, at the Wayback Machine
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ACM Turing Award Honors Innovators Who Shaped the Foundations of Programming Language Compilers and Algorithms. Retrieved March 31, 2021.
Creating Reliable Programs from Unreliable Programmers [PDF], Excellentia
Fitchard, Kevin (March 31, 2021). "Bell Labs' Al Aho and Jeffrey Ullman honored with the prestigious Turing Award". Nokia Bell Labs . Retrieved 2021.
"Profile and Detailed Achievements of the Group B Recipients of the 2017 C&C Prize" (PDF). The . NEC C&C Foundation
Aho, A. V. (1968). "Indexed Grammars---An Extension of Context-Free Grammars". Journal of the ACM. 15 (4): 647-671. doi: 10.1145/321479.321488. S2CID 9539666.
Aho, A. V. (1969). "Nested Stack Automata". Journal of the ACM. 16 (3): 383-406. doi: 10.1145/321526.321529. S2CID 685569.
Rambow, Owen; Satta, Giorgio (July 28, 1999). "Independent parallelism in finite copying parallel rewriting systems". Theoretical Computer Science. 223 (1-2): 87-120. doi: 10.1016/S0304-3975(97)00190-4. ISSN 0304-3975.
Culik, Karel; Maibaum, T. S. E. (1974). Loeckx, Jacques (ed.). "Parallel Rewriting Systems on Terms". Automata, Languages and Programming. Lecture Notes in Computer Science. Berlin, Heidelberg: Springer. 14: 495-510. doi: 10.1007/978-3-662-21545-6_38. ISBN . 978-3-662-21545-6
Aho, Alfred V.; Corasick, Margaret J. (June 1975). "Efficient String Matching: An Aid to Bibliographic Search". . Communications of the ACM 18 (6): 333-340. doi: 10.1145/360825.360855. S2CID 207735784.
Aho, A. V.; Johnson, S. C.; Ullman, J. D. (1977). "Code Generation for Expressions with Common Subexpressions". Journal of the ACM. 24: 146-160. doi: 10.1145/321992.322001. S2CID 2614214.
Morris, Richard (October 1, 2009). "Stephen Curtis Johnson: Geek of the Week". Red Gate Software . Retrieved 2018.
Lesk, M.E.; Schmidt, E. "Lex - A Lexical Analyzer Generator" . Retrieved 2010.
Levine, John R.; Mason, Tony; Brown, Doug (1992). (2 ed.). lex & yacc O'Reilly. pp. 1-2. ISBN . 1-56592-000-7
"DYOL: Design Your Own Language -- corpus -- Dragon Books -- Purple Dragon". slebok.github.io . Retrieved 2021.
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Ibaraki, Stephen. "Jeffrey Ullman And Alfred Aho, 2020 ACM A.M.Turing Award Recipients". forbes.com . Retrieved 2021.
Aho, A. V.; Kernighan, B. W.; Weinberger, P. J. (1979). "Awk -- a pattern scanning and processing language". Software: Practice and Experience. 9 (4): 267. CiteSeerX . 10.1.1.80.4787 doi: 10.1002/spe.4380090403. S2CID 29399630.
"Google Scholar Record for Alfred Aho".
"Book of Members, 1780-2010: Chapter A" (PDF). American Academy of Arts and Sciences. Archived (PDF) from the original on May 10, 2011 . Retrieved 2011.
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"DLS - Alfred Aho". Cheriton School of Computer Science. February 16, 2017 . Retrieved 2021.
Do, Liz. ". 'Nobel Prize of computing:' U of T Engineering alumnus Alfred Aho receives A.M. Turing Award" utoronto.ca . Retrieved 2021.
"Brief U.S. Suppression of Proof Stirs Anger". The New York Times. February 17, 1987 . Retrieved 2015 – via Safari.
"2017 C&C Prize Ceremony". NEC C&C Foundation . Retrieved 2021.
"Watch: Computer Scientist Alfred Aho". Simons Foundation. July 18, 2013 . Retrieved 2021.
. Currents in the theory of computing, edited by Alfred V. Aho. Contributing authors: Ronald V. Book [and others] worldcat.org. OCLC 976868524 . Retrieved 2021.
. Foundations of computer science worldcat.org. OCLC 24669768 . Retrieved 2021.
"Foundations of computer science". worldcat.org . Retrieved 2021.