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Regular Expressions using Ruby Assignment: Midterm Class: CPSC5135U – Programming Languages Teacher: Dr. Woolbright Student: James Bowman.

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Presentation on theme: "Regular Expressions using Ruby Assignment: Midterm Class: CPSC5135U – Programming Languages Teacher: Dr. Woolbright Student: James Bowman."— Presentation transcript:

1 Regular Expressions using Ruby Assignment: Midterm Class: CPSC5135U – Programming Languages Teacher: Dr. Woolbright Student: James Bowman

2 Regular Expression Definition  Regular Expressions provides a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters.  Examples: Social Security Number(XXX-XX-XXXX), Telephone number(XXX-XXX-XXXX), or phrases to check for(“Cat Name: XXXX”).

3 Regular Expression Modifiers ModifierDescription iIgnore case when matching text. oPerform #{} interpolations only once, the first time the regexp literal is evaluated. xIgnores whitespace and allows comments in regular expressions mMatches multiple lines, recognizing newlines as normal characters u,e,s,nInterpret the regexp as Unicode (UTF- 8), EUC, SJIS, or ASCII. If none of these modifiers is specified, the regular expression is assumed to use the source encoding.

4 Regular Expression Patterns Pattern:Description: ^Matches beginning of line. $Matches end of line..Matches any single character except newline. Using m option allows it to match newline as well. [...]Matches any single character in brackets. [^...]Matches any single character not in brackets re*Matches 0 or more occurrences of preceding expression. re+Matches 1 or more occurrence of preceding expression. re?Matches 0 or 1 occurrence of preceding expression. re{ n}Matches exactly n number of occurrences of preceding expression. re{ n,}Matches n or more occurrences of preceding expression. re{ n, m}Matches at least n and at most m occurrences of preceding expression.

5 Regular Expression Patterns Cont… Pattern: Description: a| bMatches either a or b. (re)Groups regular expressions and remembers matched text. (?imx)Temporarily toggles on i, m, or x options within a regular expression. If in parentheses, only that area is affected. (?-imx)Temporarily toggles off i, m, or x options within a regular expression. If in parentheses, only that area is affected. (?: re)Groups regular expressions without remembering matched text. (?imx: re)Temporarily toggles on i, m, or x options within parentheses. (?-imx: re)Temporarily toggles off i, m, or x options within parentheses. (?#...)Comment. (?= re)Specifies position using a pattern. Doesn't have a range. (?! re)Specifies position using pattern negation. Doesn't have a range. (?> re)Matches independent pattern without backtracking.

6 Regular Expression Patterns Cont… Pattern: Description: \wMatches word characters. \WMatches nonword characters. \sMatches whitespace. Equivalent to [\t\n\r\f]. \SMatches nonwhitespace. \dMatches digits. Equivalent to [0-9]. \DMatches nondigits. \AMatches beginning of string. \ZMatches end of string. If a newline exists, it matches just before newline. \zMatches end of string. \GMatches point where last match finished. \bMatches word boundaries when outside brackets. Matches backspace (0x08) when inside brackets. \BMatches nonword boundaries. \n, \t, etc.Matches newlines, carriage returns, tabs, etc. \1...\9Matches nth grouped subexpression. \10Matches nth grouped subexpression if it matched already. Otherwise refers to the octal representation of a character code.

7 Regular Expression Examples Example:Description: /[Rr]uby/Match "Ruby" or "ruby" /rub[ye]/Match "ruby" or "rube" /[aeiou]/Match any one lowercase vowel /[0-9]/Match any digit; same as /[ ]/ /[a-z]/Match any lowercase ASCII letter /[A-Z]/Match any uppercase ASCII letter /[a-zA-Z0-9]/Match any of the above /[^aeiou]/Match anything other than a lowercase vowel /[^0-9]/Match anything other than a digit Character classes:

8 Regular Expression Examples Example:Description: /./Match any character except newline /./mIn multiline mode. matches newline, too /\d/Match a digit: /[0-9]/ /\D/Match a nondigit: /[^0-9]/ /\s/Match a whitespace character: /[ \t\r\n\f]/ /\S/Match nonwhitespace: /[^ \t\r\n\f]/ /\w/Match a single word character: /[A-Za- z0-9_]/ /\W/Match a nonword character: /[^A-Za- z0-9_]/ Special Character Classes:

9 Regular Expression Examples Example:Description: /ruby|rube/Match "ruby" or "rube" /rub(y|le))/Match "ruby" or "ruble" /ruby(!+|\?)/"ruby" followed by one or more ! or one ? Alternatives:

10 Regular Expression Examples ExampleDescription /^Ruby/Match "Ruby" at the start of a string or internal line /Ruby$/Match "Ruby" at the end of a string or line /\ARuby/Match "Ruby" at the start of a string /Ruby\Z/Match "Ruby" at the end of a string /\bRuby\b/Match "Ruby" at a word boundary /\brub\B/\B is nonword boundary: match "rub" in "rube" and "ruby" but not alone /Ruby(?=!)/Match "Ruby", if followed by an exclamation point /Ruby(?!!)/Match "Ruby", if not followed by an exclamation point Anchors:

11 Regexp Class  A Regexp holds a regular expression, used to match a pattern against strings. Regexps are created using the /…/ and %r{…} literals, and by the Regexp::new constructor.

12 Regexp Class  Escape:  Escapes any characters that would have special meaning in a regular expression. Example: Regexp.escape('\*?{}.') #=> \\\*\?\{\}\.

13 Regexp Class  New:  Constructs a new regular expression from pattern, which can be a string. Example: r1 = Regexp.new('^a- z+:\\s+\w+') #=> /^a-z+:\s+\w+/

14 Search and Replace Example #!/usr/bin/ruby phone = " #This is Phone Number" # Delete Ruby-style comments phone = phone.sub!(/#.*$/, "") puts "Phone Num : #{phone}" # Remove anything other than digits phone = phone.gsub!(/\D/, "") puts "Phone Num : #{phone}" Result: Phone Num : Phone Num :

15 Code Example – Matching on Strings #!/usr/bin/ruby line1 = “People are smarter than dogs"; line2 = "Dogs also like cats"; if ( line1 =~ /People(.*)/ ) puts "Line1 starts with People" end if ( line2 =~ /People(.*)/ ) puts "Line2 starts with Dogs" end Result: Line1 starts with People

16 Code Examples Please See Attached Code for more examples


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