Regular Expressions with a Brief Intro to FSM
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Use Perl Regular Expressions in SAS® Shuguang Zhang, WRDS, Philadelphia, PA
NESUG 2007 Programming Beyond the Basics Use Perl Regular Expressions in SAS® Shuguang Zhang, WRDS, Philadelphia, PA ABSTRACT Regular Expression (Regexp) enhance search and replace operations on text. In SAS®, the INDEX, SCAN and SUBSTR functions along with concatenation (||) can be used for simple search and replace operations on static text. These functions lack flexibility and make searching dynamic text difficult, and involve more function calls. Regexp combines most, if not all, of these steps into one expression. This makes code less error prone, easier to maintain, clearer, and can improve performance. This paper will discuss three ways to use Perl Regular Expression in SAS: 1. Use SAS PRX functions; 2. Use Perl Regular Expression with filename statement through a PIPE such as ‘Filename fileref PIPE 'Perl programm'; 3. Use an X command such as ‘X Perl_program’; Three typical uses of regular expressions will also be discussed and example(s) will be presented for each: 1. Test for a pattern of characters within a string; 2. Replace text; 3. Extract a substring. INTRODUCTION Perl is short for “Practical Extraction and Report Language". Larry Wall Created Perl in mid-1980s when he was trying to produce some reports from a Usenet-Nes-like hierarchy of files. Perl tries to fill the gap between low-level programming and high-level programming and it is easy, nearly unlimited, and fast. A regular expression, often called a pattern in Perl, is a template that either matches or does not match a given string. That is, there are an infinite number of possible text strings. -
Lecture 18: Theory of Computation Regular Expressions and Dfas
Introduction to Theoretical CS Lecture 18: Theory of Computation Two fundamental questions. ! What can a computer do? ! What can a computer do with limited resources? General approach. Pentium IV running Linux kernel 2.4.22 ! Don't talk about specific machines or problems. ! Consider minimal abstract machines. ! Consider general classes of problems. COS126: General Computer Science • http://www.cs.Princeton.EDU/~cos126 2 Why Learn Theory In theory . Regular Expressions and DFAs ! Deeper understanding of what is a computer and computing. ! Foundation of all modern computers. ! Pure science. ! Philosophical implications. a* | (a*ba*ba*ba*)* In practice . ! Web search: theory of pattern matching. ! Sequential circuits: theory of finite state automata. a a a ! Compilers: theory of context free grammars. b b ! Cryptography: theory of computational complexity. 0 1 2 ! Data compression: theory of information. b "In theory there is no difference between theory and practice. In practice there is." -Yogi Berra 3 4 Pattern Matching Applications Regular Expressions: Basic Operations Test if a string matches some pattern. Regular expression. Notation to specify a set of strings. ! Process natural language. ! Scan for virus signatures. ! Search for information using Google. Operation Regular Expression Yes No ! Access information in digital libraries. ! Retrieve information from Lexis/Nexis. Concatenation aabaab aabaab every other string ! Search-and-replace in a word processors. cumulus succubus Wildcard .u.u.u. ! Filter text (spam, NetNanny, Carnivore, malware). jugulum tumultuous ! Validate data-entry fields (dates, email, URL, credit card). aa Union aa | baab baab every other string ! Search for markers in human genome using PROSITE patterns. aa ab Closure ab*a abbba ababa Parse text files. -
Perl Regular Expressions Tip Sheet Functions and Call Routines
– Perl Regular Expressions Tip Sheet Functions and Call Routines Basic Syntax Advanced Syntax regex-id = prxparse(perl-regex) Character Behavior Character Behavior Compile Perl regular expression perl-regex and /…/ Starting and ending regex delimiters non-meta Match character return regex-id to be used by other PRX functions. | Alternation character () Grouping {}[]()^ Metacharacters, to match these pos = prxmatch(regex-id | perl-regex, source) $.|*+?\ characters, override (escape) with \ Search in source and return position of match or zero Wildcards/Character Class Shorthands \ Override (escape) next metacharacter if no match is found. Character Behavior \n Match capture buffer n Match any one character . (?:…) Non-capturing group new-string = prxchange(regex-id | perl-regex, times, \w Match a word character (alphanumeric old-string) plus "_") Lazy Repetition Factors Search and replace times number of times in old- \W Match a non-word character (match minimum number of times possible) string and return modified string in new-string. \s Match a whitespace character Character Behavior \S Match a non-whitespace character *? Match 0 or more times call prxchange(regex-id, times, old-string, new- \d Match a digit character +? Match 1 or more times string, res-length, trunc-value, num-of-changes) Match a non-digit character ?? Match 0 or 1 time Same as prior example and place length of result in \D {n}? Match exactly n times res-length, if result is too long to fit into new-string, Character Classes Match at least n times trunc-value is set to 1, and the number of changes is {n,}? Character Behavior Match at least n but not more than m placed in num-of-changes. -
Unicode Regular Expressions Technical Reports
7/1/2019 UTS #18: Unicode Regular Expressions Technical Reports Working Draft for Proposed Update Unicode® Technical Standard #18 UNICODE REGULAR EXPRESSIONS Version 20 Editors Mark Davis, Andy Heninger Date 2019-07-01 This Version http://www.unicode.org/reports/tr18/tr18-20.html Previous Version http://www.unicode.org/reports/tr18/tr18-19.html Latest Version http://www.unicode.org/reports/tr18/ Latest Proposed http://www.unicode.org/reports/tr18/proposed.html Update Revision 20 Summary This document describes guidelines for how to adapt regular expression engines to use Unicode. Status This is a draft document which may be updated, replaced, or superseded by other documents at any time. Publication does not imply endorsement by the Unicode Consortium. This is not a stable document; it is inappropriate to cite this document as other than a work in progress. A Unicode Technical Standard (UTS) is an independent specification. Conformance to the Unicode Standard does not imply conformance to any UTS. Please submit corrigenda and other comments with the online reporting form [Feedback]. Related information that is useful in understanding this document is found in the References. For the latest version of the Unicode Standard, see [Unicode]. For a list of current Unicode Technical Reports, see [Reports]. For more information about versions of the Unicode Standard, see [Versions]. Contents 0 Introduction 0.1 Notation 0.2 Conformance 1 Basic Unicode Support: Level 1 1.1 Hex Notation 1.1.1 Hex Notation and Normalization 1.2 Properties 1.2.1 General -
Regular Expressions
CS 172: Computability and Complexity Regular Expressions Sanjit A. Seshia EECS, UC Berkeley Acknowledgments: L.von Ahn, L. Blum, M. Blum The Picture So Far DFA NFA Regular language S. A. Seshia 2 Today’s Lecture DFA NFA Regular Regular language expression S. A. Seshia 3 Regular Expressions • What is a regular expression? S. A. Seshia 4 Regular Expressions • Q. What is a regular expression? • A. It’s a “textual”/ “algebraic” representation of a regular language – A DFA can be viewed as a “pictorial” / “explicit” representation • We will prove that a regular expressions (regexps) indeed represent regular languages S. A. Seshia 5 Regular Expressions: Definition σ is a regular expression representing { σσσ} ( σσσ ∈∈∈ ΣΣΣ ) ε is a regular expression representing { ε} ∅ is a regular expression representing ∅∅∅ If R 1 and R 2 are regular expressions representing L 1 and L 2 then: (R 1R2) represents L 1⋅⋅⋅L2 (R 1 ∪∪∪ R2) represents L 1 ∪∪∪ L2 (R 1)* represents L 1* S. A. Seshia 6 Operator Precedence 1. *** 2. ( often left out; ⋅⋅⋅ a ··· b ab ) 3. ∪∪∪ S. A. Seshia 7 Example of Precedence R1*R 2 ∪∪∪ R3 = ( ())R1* R2 ∪∪∪ R3 S. A. Seshia 8 What’s the regexp? { w | w has exactly a single 1 } 0*10* S. A. Seshia 9 What language does ∅∅∅* represent? {ε} S. A. Seshia 10 What’s the regexp? { w | w has length ≥ 3 and its 3rd symbol is 0 } ΣΣΣ2 0 ΣΣΣ* Σ = (0 ∪∪∪ 1) S. A. Seshia 11 Some Identities Let R, S, T be regular expressions • R ∪∪∪∅∅∅ = ? • R ···∅∅∅ = ? • Prove: R ( S ∪∪∪ T ) = R S ∪∪∪ R T (what’s the proof idea?) S. -
Context-Free Grammar for the Syntax of Regular Expression Over the ASCII
Context-free Grammar for the syntax of regular expression over the ASCII character set assumption : • A regular expression is to be interpreted a Haskell string, then is used to match against a Haskell string. Therefore, each regexp is enclosed inside a pair of double quotes, just like any Haskell string. For clarity, a regexp is highlighted and a “Haskell input string” is quoted for the examples in this document. • Since ASCII character strings will be encoded as in Haskell, therefore special control ASCII characters such as NUL and DEL are handled by Haskell. context-free grammar : BNF notation is used to describe the syntax of regular expressions defined in this document, with the following basic rules: • <nonterminal> ::= choice1 | choice2 | ... • Double quotes are used when necessary to reflect the literal meaning of the content itself. <regexp> ::= <union> | <concat> <union> ::= <regexp> "|" <concat> <concat> ::= <term><concat> | <term> <term> ::= <star> | <element> <star> ::= <element>* <element> ::= <group> | <char> | <emptySet> | <emptyStr> <group> ::= (<regexp>) <char> ::= <alphanum> | <symbol> | <white> <alphanum> ::= A | B | C | ... | Z | a | b | c | ... | z | 0 | 1 | 2 | ... | 9 <symbol> ::= ! | " | # | $ | % | & | ' | + | , | - | . | / | : | ; | < | = | > | ? | @ | [ | ] | ^ | _ | ` | { | } | ~ | <sp> | \<metachar> <sp> ::= " " <metachar> ::= \ | "|" | ( | ) | * | <white> <white> ::= <tab> | <vtab> | <nline> <tab> ::= \t <vtab> ::= \v <nline> ::= \n <emptySet> ::= Ø <emptyStr> ::= "" Explanations : 1. Definition of <metachar> in our definition of regexp: Symbol meaning \ Used to escape a metacharacter, \* means the star char itself | Specifies alternatives, y|n|m means y OR n OR m (...) Used for grouping, giving the group priority * Used to indicate zero or more of a regexp, a* matches the empty string, “a”, “aa”, “aaa” and so on Whi tespace char meaning \n A new line character \t A horizontal tab character \v A vertical tab character 2. -
Generating Context-Free Grammars Using Classical Planning
Proceedings of the Twenty-Sixth International Joint Conference on Artificial Intelligence (IJCAI-17) Generating Context-Free Grammars using Classical Planning Javier Segovia-Aguas1, Sergio Jimenez´ 2, Anders Jonsson 1 1 Universitat Pompeu Fabra, Barcelona, Spain 2 University of Melbourne, Parkville, Australia [email protected], [email protected], [email protected] Abstract S ! aSa S This paper presents a novel approach for generating S ! bSb /|\ Context-Free Grammars (CFGs) from small sets of S ! a S a /|\ input strings (a single input string in some cases). a S a Our approach is to compile this task into a classical /|\ planning problem whose solutions are sequences b S b of actions that build and validate a CFG compli- | ant with the input strings. In addition, we show that our compilation is suitable for implementing the two canonical tasks for CFGs, string produc- (a) (b) tion and string recognition. Figure 1: (a) Example of a context-free grammar; (b) the corre- sponding parse tree for the string aabbaa. 1 Introduction A formal grammar is a set of symbols and rules that describe symbols in the grammar and (2), a bounded maximum size of how to form the strings of certain formal language. Usually the rules in the grammar (i.e. a maximum number of symbols two tasks are defined over formal grammars: in the right-hand side of the grammar rules). Our approach is compiling this inductive learning task into • Production : Given a formal grammar, generate strings a classical planning task whose solutions are sequences of ac- that belong to the language represented by the grammar. -
PHP Regular Expressions
PHP Regular Expressions What is Regular Expression Regular Expressions, commonly known as "regex" or "RegExp", are a specially formatted text strings used to find patterns in text. Regular expressions are one of the most powerful tools available today for effective and efficient text processing and manipulations. For example, it can be used to verify whether the format of data i.e. name, email, phone number, etc. entered by the user was correct or not, find or replace matching string within text content, and so on. PHP (version 5.3 and above) supports Perl style regular expressions via its preg_ family of functions. Why Perl style regular expressions? Because Perl (Practical Extraction and Report Language) was the first mainstream programming language that provided integrated support for regular expressions and it is well known for its strong support of regular expressions and its extraordinary text processing and manipulation capabilities. Let's begin with a brief overview of the commonly used PHP's built-in pattern- matching functions before delving deep into the world of regular expressions. Function What it Does preg_match() Perform a regular expression match. preg_match_all() Perform a global regular expression match. preg_replace() Perform a regular expression search and replace. preg_grep() Returns the elements of the input array that matched the pattern. preg_split() Splits up a string into substrings using a regular expression. preg_quote() Quote regular expression characters found within a string. Note: The PHP preg_match() function stops searching after it finds the first match, whereas the preg_match_all() function continues searching until the end of the string and find all possible matches instead of stopping at the first match. -
Formal Grammar Specifications of User Interface Processes
FORMAL GRAMMAR SPECIFICATIONS OF USER INTERFACE PROCESSES by MICHAEL WAYNE BATES ~ Bachelor of Science in Arts and Sciences Oklahoma State University Stillwater, Oklahoma 1982 Submitted to the Faculty of the Graduate College of the Oklahoma State University iri partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE July, 1984 I TheSIS \<-)~~I R 32c-lf CO'f· FORMAL GRAMMAR SPECIFICATIONS USER INTER,FACE PROCESSES Thesis Approved: 'Dean of the Gra uate College ii tta9zJ1 1' PREFACE The benefits and drawbacks of using a formal grammar model to specify a user interface has been the primary focus of this study. In particular, the regular grammar and context-free grammar models have been examined for their relative strengths and weaknesses. The earliest motivation for this study was provided by Dr. James R. VanDoren at TMS Inc. This thesis grew out of a discussion about the difficulties of designing an interface that TMS was working on. I would like to express my gratitude to my major ad visor, Dr. Mike Folk for his guidance and invaluable help during this study. I would also like to thank Dr. G. E. Hedrick and Dr. J. P. Chandler for serving on my graduate committee. A special thanks goes to my wife, Susan, for her pa tience and understanding throughout my graduate studies. iii TABLE OF CONTENTS Chapter Page I. INTRODUCTION . II. AN OVERVIEW OF FORMAL LANGUAGE THEORY 6 Introduction 6 Grammars . • . • • r • • 7 Recognizers . 1 1 Summary . • • . 1 6 III. USING FOR~AL GRAMMARS TO SPECIFY USER INTER- FACES . • . • • . 18 Introduction . 18 Definition of a User Interface 1 9 Benefits of a Formal Model 21 Drawbacks of a Formal Model . -
A Quick Guide to PERL Regular Expressions Second Edition © 2006 Transliteration: Translate Operator Tr/// EXPR =~ Tr/SEARCHLIST/REPLACELIST/Cds
\W Any non-word character. Warning \w != \S Search&Replace: substitution operator s/// A Quick Guide To EXPR =~ s/MOTIF/REPLACE/egimosx POSIX Character class PERL Regular Expressions Example: correct typo for the word rabbit [[:class:]] class can be any of: $ex =~ s/rabit/rabbit/g; alnum alpha ascii blank cntrl digit graph lower This is a Quick reference Guide for PERL regular expressions Here is the content of $ex: print punct space upper xdigit (also known as regexps or regexes). The ID sp:UBP5_RAT is similar to the rabbit AC tr:Q12345 These tools are used to describe text as “motifs” or “patterns” for matching, quoting, substituting or translitterating. Each Example: find and tag any TrEMBL AC Special characters programming language (Perl, C, Java, Python...) define its $ex =~ s/tr:/trembl_ac=/g; \a alert (bell) Here is the content of $ex: own regular expressions although the syntax might differ from \b backspace details to extensive changes. In this guide we will concentrate The ID sp:UBP5_RAT is similar to the rabit AC trembl_ \e escape ac=Q12345 on the Perl regexp syntax, we assume that the reader has some \f form feed preliminary knowledge of Perl programming. Options \n newline \r carriage return e evaluate REPLACE as an expression Perl uses a Traditional Nondeterministic Finite Automata \t horizontal tabulation (NFA) match engine. This means that it will compare each g global matches (matches all occurrences) element of the motif to the input string, keeping track of i case insensitive \nnn octal nnn the positions. The engine choose the first leftmost match m multiline, allow “^” and “$” to match with (\n) \xnn hexadecimal nn after greedy (i.e., longest possible match) quantifiers have o compile MOTIF only once \cX control character X matched. -
Algorithm for Analysis and Translation of Sentence Phrases
Masaryk University Faculty}w¡¢£¤¥¦§¨ of Informatics!"#$%&'()+,-./012345<yA| Algorithm for Analysis and Translation of Sentence Phrases Bachelor’s thesis Roman Lacko Brno, 2014 Declaration Hereby I declare, that this paper is my original authorial work, which I have worked out by my own. All sources, references and literature used or excerpted during elaboration of this work are properly cited and listed in complete reference to the due source. Roman Lacko Advisor: RNDr. David Sehnal ii Acknowledgement I would like to thank my family and friends for their support. Special thanks go to my supervisor, RNDr. David Sehnal, for his attitude and advice, which was of invaluable help while writing this thesis; and my friend František Silváši for his help with the revision of this text. iii Abstract This thesis proposes a library with an algorithm capable of translating objects described by natural language phrases into their formal representations in an object model. The solution is not restricted by a specific language nor target model. It features a bottom-up chart parser capable of parsing any context-free grammar. Final translation of parse trees is carried out by the interpreter that uses rewrite rules provided by the target application. These rules can be extended by custom actions, which increases the usability of the library. This functionality is demonstrated by an additional application that translates description of motifs in English to objects of the MotiveQuery language. iv Keywords Natural language, syntax analysis, chart parsing, -
Finite-State Automata and Algorithms
Finite-State Automata and Algorithms Bernd Kiefer, [email protected] Many thanks to Anette Frank for the slides MSc. Computational Linguistics Course, SS 2009 Overview . Finite-state automata (FSA) – What for? – Recap: Chomsky hierarchy of grammars and languages – FSA, regular languages and regular expressions – Appropriate problem classes and applications . Finite-state automata and algorithms – Regular expressions and FSA – Deterministic (DFSA) vs. non-deterministic (NFSA) finite-state automata – Determinization: from NFSA to DFSA – Minimization of DFSA . Extensions: finite-state transducers and FST operations Finite-state automata: What for? Chomsky Hierarchy of Hierarchy of Grammars and Languages Automata . Regular languages . Regular PS grammar (Type-3) Finite-state automata . Context-free languages . Context-free PS grammar (Type-2) Push-down automata . Context-sensitive languages . Tree adjoining grammars (Type-1) Linear bounded automata . Type-0 languages . General PS grammars Turing machine computationally more complex less efficient Finite-state automata model regular languages Regular describe/specify expressions describe/specify Finite describe/specify Regular automata recognize languages executable! Finite-state MACHINE Finite-state automata model regular languages Regular describe/specify expressions describe/specify Regular Finite describe/specify Regular grammars automata recognize/generate languages executable! executable! • properties of regular languages • appropriate problem classes Finite-state • algorithms for FSA MACHINE Languages, formal languages and grammars . Alphabet Σ : finite set of symbols Σ . String : sequence x1 ... xn of symbols xi from the alphabet – Special case: empty string ε . Language over Σ : the set of strings that can be generated from Σ – Sigma star Σ* : set of all possible strings over the alphabet Σ Σ = {a, b} Σ* = {ε, a, b, aa, ab, ba, bb, aaa, aab, ...} – Sigma plus Σ+ : Σ+ = Σ* -{ε} Strings – Special languages: ∅ = {} (empty language) ≠ {ε} (language of empty string) .