Regex in Ruby – Turing

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Regex in Ruby – Turing

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Regex in Ruby

Turing

Osama Alghanmi / @itechdom

What is Regular Expression

  • Regular expressions allow matching and manipulation of textual data.
  • Abbreviated as regex.

Using Regular Expressions

  • Scan a string for multiple occurrences of a pattern.
  • Replace part of a string with another string.
  • Split a string based on a matching separator.

Regular Expression Syntax

  • Regular expressions are put between two forward slashes (/match_me/)

Regex Basics

  • [abc] A single character: a, b or c
  • [^abc] Any single character but a, b, or c
  • [a-z] Any single character in the range a-z
  • [a-zA-Z] Any single character in the range a-z or A-Z
  • [1-9] any number between 1 and 9
  • ^ Start of line
  • $ End of line
  • \A Start of string
  • \z End of string

Shortcuts (meta characters)

  • . Any single character
  • \s Any whitespace character
  • \S Any non-whitespace character
  • \d Any digit
  • \D Any non-digit
  • \w Any word character (letter, number, underscore)
  • \W Any non-word character
  • \b Any word boundary character

Groups

  • (...) Capture everything enclosed
  • (a|b) a or b
  • ? Zero or one of a
  • * Zero or more of a
  • + One or more of a
  • {3} Exactly 3 of a
  • {3,} 3 or more of a
  • a{3,6} Between 3 and 6 of a

Characters that needs to be escaped.

  • They are escaped with a backward slash \\
  • Characters are:
. | ( ) [ ] { } + \ ^ $ * ?

Ways to Use Regex in Ruby

  • Match
  • Scan
  • =~
  • Gsub
  • Split
a = /a/

a.class # Regexp

myString = "A woman once said. A man once said. A child once said"

match = myString.match(a) #this will return a

match = myString.scan(a) #this will return ["a", "a", "a", "a", "a"]

match = myString.gsub(a,"b") #this will replace all a(s) with b, leaving behind capital A

myString =~ a #return the index of the first occurance 

match = myString.split(a) # split a string by a(s)

Exercise

Find the pattern used to match the following:

  • s@sos a@aaa b@a
  • zzz@a.com zz@a.com
  • 12 3 23 31
  • aaa
  • 2.3 3.1 3.5
  • a string that begins with hi
  • a string that ends with hello

http://rubular.com/

capturing

  • We can specify variables in regex that we can refer to later
  • The exampel below stores month, day and year when given a date.
(?<month>\d{1,2})\/(?<day>\d{1,2})\/(?<year>\d{4})

Then we can do something like this:

date_string = "06/11/1985"
pattern = /(?<month>\d{1,2})\/(?<day>\d{1,2})\/(?<year>\d{4})/
result = date_string.match(pattern)
# we can now access the days, month and year
result[:day] #11
result[:month] #06
result[:year] #1985

exercise

  • Write a pattern that will take a decimal number (ie: 3.4)
  • It captures the number in dollars and cents
  • display the dollars and cents in that number
  • You should modify the previous example
    (?<month>\d{1,2})\/(?<day>\d{1,2})\/(?<year>\d{4})