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Believe it or not, this is a regular expression! Whole words, sentences, paragraphs even can technically be called regular expressions (as long as they are in between two forward slashes). The Rubular environment highlights for us every single instance of the pattern \u2018neighbor\u2019 in our block of text \u2013 even instances where neighbor is part of a bigger word, too! That being said, you might want to find something more abstract than an exact word match. This is where metacharacters come in.<\/p>\n\n\n\n
Metacharacters<\/h2>\n\n\n\n![\"\"](\"https:\/\/careerkarma.com\/blog\/wp-content\/uploads\/2020\/07\/anas-alshanti-feXpdV001o4-unsplash.jpg\")
Using RegEx can be challenging for seasoned programmers, so don\u2019t get discouraged.<\/figcaption><\/figure>\n\n\n\nJust as atoms are the building blocks of pretty much everything we see around, metacharacters are the building blocks of regular expressions. As you add on to your regular expression, the overall pattern changes. And when the overall pattern changes, the results you get back from from the methods you use can be different.
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Listed below are several ways to modify your regular expression so you can find a pattern that works for you. There is no one absolutely right<\/em> way to write a regular expression for phone numbers or emails, etc. \u2013 it\u2019s all about what your needs are for your project. <\/p>\n\n\n\n<\/p>\n\n\n\n
Metacharacter<\/td> Matches<\/td> Example<\/td><\/tr> [abc]<\/td> A character class that matches a single character in the string that could be a, b or c
<\/td> \/[eig]\/ can match portions of neighbor, apple, or gate<\/td><\/tr> [^abc]\t<\/td> A negated character class that matches every single character in the string but<\/em><\/strong> a, b or c<\/td>\/[^eig]\/ can match portions of neighbor, apple, or gate<\/td><\/tr> [a-z]\t<\/td> A character class that matches any single character in the range a-z<\/td> \/[e-i]\/ can match single characters in portions of neighbor, apple, or gate
<\/td><\/tr> [a-zA-Z]<\/td> A character class that matches a range of characters from a-z or A-Z
<\/td> \/[e-i]\/ can match single characters in portions of \u201cHi neighbor!\u201d, Grapple, or gate<\/td><\/tr> ^\t<\/td> Start of line<\/td> \/^Hello\/ matches lines that start with \u2018Hello\u2019<\/td><\/tr> $<\/td> End of line<\/td> \/Goodbye$\/ matches lines that end in \u2018Goodbye\u2019<\/td><\/tr> \\A<\/td> Start of string. Similar to \u2018^\u2019 , but with no multiline mode<\/td> \/\\Aa\/ matches the \u2018a\u2019 in apple, but not the \u2018a\u2019 in apricot since it\u2019s not the beginning of the string:
apple
apricot<\/td><\/tr> \\z\t<\/td> End of string. Similar to \u2018$\u2019, but with no multiline mode<\/td> \/\\za\/ matches the \u2018a\u2019 in zebra, but not the \u2018a\u2019 in libra since it\u2019s not the end of the string
librazebra<\/td><\/tr> .<\/td> Wild card. Dot matches any character. <\/td> \/.\/ will match any single character in apple<\/td><\/tr> +<\/td> Matches one or more of the previous metacharacter<\/td> \/aa+\/ will match \u2018aa\u2019, \u2018aaaaaaa\u2019 but will not match \u2018a\u2019 since it has to be one or more of the previous metacharacter (which in this instance is the second a)<\/td><\/tr> *<\/td> Matches zero or more of the previous metacharacter<\/td> \/ab*\/ will match \u2018a\u2019, \u2018ab\u2019, \u2018abbbbbb\u2019<\/td><\/tr> \\s<\/td> Any whitespace character<\/td> \/^The\\s.+s$\/ will match The Beatles<\/em>, The Rolling Stones, The Cranberries, etc.<\/em><\/td><\/tr>\\S<\/td> Any non-whitespace character<\/td> \/\\S+\/ will match The Beatles<\/em>, The Rolling Stones, The Cranberries, etc.<\/em><\/td><\/tr>\\d<\/td> Any digit<\/td> \/\\d+\/ will match 22, 33333, 0, etc<\/td><\/tr> \\D<\/td> Any non-digit<\/td> \/\\D+\/ will match \u2018Hello, goodbye\u2019<\/td><\/tr> \\w<\/td> Any word character<\/td> \/ny\\w*\/ will match \u2018ny_152\u2019, \u2018nypost39\u2019, etc<\/td><\/tr> \\W<\/td> Any non-word character<\/td> \/\\W+\/ will match \u2018)(*&^%$\u2019<\/td><\/tr> a{3}<\/td> Exactly 3 of \u2018a\u2019<\/td> \/\\d{3}-\\d{3}-\\d{4}\/ will match 555-555-5555<\/td><\/tr> a{3,}<\/td> Three or more of \u2018a\u2019<\/td> \/[a-zA-Z0-9!#$^&*)(]{8,}\/ will match \u2018xE*BqRx14B7TAQp\u2019 \u21d0 which looks like it could be used as a password!<\/td><\/tr> a{3, 6}<\/td> Three to six of \u2018a\u2019<\/td> \/[a-zA-Z0-9!#$^&*)(]{8,32}\/ will match \u20180XX!pC3Odpu30Qc\u2019 because it\u2019s more than 3 and less than 32 characters in length<\/td><\/tr> a?<\/td> 0 or 1 of \u2018a\u2019<\/td> \/\\d?-\\d{3)-\\d{3}-\\d{4}\/ will match a phone number with an international code attached to front and one without an international code attached to front. <\/td><\/tr><\/tbody><\/table>\n\n\n\n<\/p>\n\n\n\n
Using metacharacters is great for validation when it comes to users filling out forms on websites. We want to make sure correct information is entered \u2013 that would be a great use of RegEx to make sure the pattern of an address or of an email or phone number is the correct format. This leads to better organized databases with less user error when registering new accounts.
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Methods to Test RegEx in Ruby<\/h2>\n\n\n\n
Here\u2019s the code we are going to use to differentiate between scan and match:
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#!\/usr\/bin\/ruby\n \nclass RegexTest\n def initialize(str, regex)\n @str = str\n @regex = regex\n @result = str.scan(regex)\n end\n def display_details()\n puts "String = #@str"\n puts "regex = #@regex"\n puts "result = #@result"\n end\nend\n# Create Objects\nstr1 = RegexTest.new("The rain in Spain stays mainly on the plain", \/\\w+ain\/)\nstr2 = RegexTest.new("In Hertford, Hereford, and Hampshire, hurricanes hardly ever happen", \/H\\w+\/)\n# Call Methods\nstr1.display_details()\nstr2.display_details()\n<\/pre><\/div>\n\n\n\n<\/p>\n\n\n\n
Scan<\/p>\n\n\n\n
The scan method in Ruby returns an array of all strings that match your regular expression:
<\/p>\n\n\n\n
str1: result = [\"rain\", \"Spain\", \"main\", \"plain\"]<\/code><\/p>\n\n\n\nstr2: result = [\"Hertford\", \"Hereford\", \"Hampshire\"]<\/code>
<\/p>\n\n\n\nThis allows you to do whatever you would like with the result.
<\/p>\n\n\n\n
RegExp Match<\/p>\n\n\n\n
The regular expression Match method is very, VERY similar to scan, but finds the first instance of a match instead of all matches. Change @result = str.scan(regex) to @result = str.match(regex) to take a look at the difference:
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str1: result = rain<\/code><\/p>\n\n\n\nstr2: result = Hertford<\/code>
<\/p>\n\n\n\nMatch, however, returns a <Matchdata> object. It\u2019s got some methods associated with it that can be used in your logic when you use your results. Take a look at the Ruby<\/a> docs for more information on what you could use there.
<\/p>\n\n\n\nGrep<\/p>\n\n\n\n
Grep is an enumerable method for finding matching strings in arrays. It will return an array of all strings that match your regular expression. With the code we have, we have to make sure that the string we passed in is split up into an array.
<\/p>\n\n\n\n
To do this change this line of code:<\/p>\n\n\n\n
Just as atoms are the building blocks of pretty much everything we see around, metacharacters are the building blocks of regular expressions. As you add on to your regular expression, the overall pattern changes. And when the overall pattern changes, the results you get back from from the methods you use can be different.
<\/p>\n\n\n\n
Listed below are several ways to modify your regular expression so you can find a pattern that works for you. There is no one absolutely right<\/em> way to write a regular expression for phone numbers or emails, etc. \u2013 it\u2019s all about what your needs are for your project. <\/p>\n\n\n\n <\/p>\n\n\n\n <\/p>\n\n\n\n Using metacharacters is great for validation when it comes to users filling out forms on websites. We want to make sure correct information is entered \u2013 that would be a great use of RegEx to make sure the pattern of an address or of an email or phone number is the correct format. This leads to better organized databases with less user error when registering new accounts. Here\u2019s the code we are going to use to differentiate between scan and match: <\/p>\n\n\n\n Scan<\/p>\n\n\n\n The scan method in Ruby returns an array of all strings that match your regular expression: str1: str2: This allows you to do whatever you would like with the result. RegExp Match<\/p>\n\n\n\n The regular expression Match method is very, VERY similar to scan, but finds the first instance of a match instead of all matches. Change @result = str.scan(regex) to @result = str.match(regex) to take a look at the difference: str1: str2: Match, however, returns a <Matchdata> object. It\u2019s got some methods associated with it that can be used in your logic when you use your results. Take a look at the Ruby<\/a> docs for more information on what you could use there. Grep<\/p>\n\n\n\n Grep is an enumerable method for finding matching strings in arrays. It will return an array of all strings that match your regular expression. With the code we have, we have to make sure that the string we passed in is split up into an array. To do this change this line of code:<\/p>\n\n\n\nMetacharacter<\/td> Matches<\/td> Example<\/td><\/tr> [abc]<\/td> A character class that matches a single character in the string that could be a, b or c
<\/td>\/[eig]\/ can match portions of neighbor, apple, or gate<\/td><\/tr> [^abc]\t<\/td> A negated character class that matches every single character in the string but<\/em><\/strong> a, b or c<\/td> \/[^eig]\/ can match portions of neighbor, apple, or gate<\/td><\/tr> [a-z]\t<\/td> A character class that matches any single character in the range a-z<\/td> \/[e-i]\/ can match single characters in portions of neighbor, apple, or gate
<\/td><\/tr>[a-zA-Z]<\/td> A character class that matches a range of characters from a-z or A-Z
<\/td>\/[e-i]\/ can match single characters in portions of \u201cHi neighbor!\u201d, Grapple, or gate<\/td><\/tr> ^\t<\/td> Start of line<\/td> \/^Hello\/ matches lines that start with \u2018Hello\u2019<\/td><\/tr> $<\/td> End of line<\/td> \/Goodbye$\/ matches lines that end in \u2018Goodbye\u2019<\/td><\/tr> \\A<\/td> Start of string. Similar to \u2018^\u2019 , but with no multiline mode<\/td> \/\\Aa\/ matches the \u2018a\u2019 in apple, but not the \u2018a\u2019 in apricot since it\u2019s not the beginning of the string:
apple
apricot<\/td><\/tr>\\z\t<\/td> End of string. Similar to \u2018$\u2019, but with no multiline mode<\/td> \/\\za\/ matches the \u2018a\u2019 in zebra, but not the \u2018a\u2019 in libra since it\u2019s not the end of the string
librazebra<\/td><\/tr>.<\/td> Wild card. Dot matches any character. <\/td> \/.\/ will match any single character in apple<\/td><\/tr> +<\/td> Matches one or more of the previous metacharacter<\/td> \/aa+\/ will match \u2018aa\u2019, \u2018aaaaaaa\u2019 but will not match \u2018a\u2019 since it has to be one or more of the previous metacharacter (which in this instance is the second a)<\/td><\/tr> *<\/td> Matches zero or more of the previous metacharacter<\/td> \/ab*\/ will match \u2018a\u2019, \u2018ab\u2019, \u2018abbbbbb\u2019<\/td><\/tr> \\s<\/td> Any whitespace character<\/td> \/^The\\s.+s$\/ will match The Beatles<\/em>, The Rolling Stones, The Cranberries, etc.<\/em><\/td><\/tr> \\S<\/td> Any non-whitespace character<\/td> \/\\S+\/ will match The Beatles<\/em>, The Rolling Stones, The Cranberries, etc.<\/em><\/td><\/tr> \\d<\/td> Any digit<\/td> \/\\d+\/ will match 22, 33333, 0, etc<\/td><\/tr> \\D<\/td> Any non-digit<\/td> \/\\D+\/ will match \u2018Hello, goodbye\u2019<\/td><\/tr> \\w<\/td> Any word character<\/td> \/ny\\w*\/ will match \u2018ny_152\u2019, \u2018nypost39\u2019, etc<\/td><\/tr> \\W<\/td> Any non-word character<\/td> \/\\W+\/ will match \u2018)(*&^%$\u2019<\/td><\/tr> a{3}<\/td> Exactly 3 of \u2018a\u2019<\/td> \/\\d{3}-\\d{3}-\\d{4}\/ will match 555-555-5555<\/td><\/tr> a{3,}<\/td> Three or more of \u2018a\u2019<\/td> \/[a-zA-Z0-9!#$^&*)(]{8,}\/ will match \u2018xE*BqRx14B7TAQp\u2019 \u21d0 which looks like it could be used as a password!<\/td><\/tr> a{3, 6}<\/td> Three to six of \u2018a\u2019<\/td> \/[a-zA-Z0-9!#$^&*)(]{8,32}\/ will match \u20180XX!pC3Odpu30Qc\u2019 because it\u2019s more than 3 and less than 32 characters in length<\/td><\/tr> a?<\/td> 0 or 1 of \u2018a\u2019<\/td> \/\\d?-\\d{3)-\\d{3}-\\d{4}\/ will match a phone number with an international code attached to front and one without an international code attached to front. <\/td><\/tr><\/tbody><\/table>\n\n\n\n
<\/p>\n\n\n\nMethods to Test RegEx in Ruby<\/h2>\n\n\n\n
<\/p>\n\n\n\n#!\/usr\/bin\/ruby\n \nclass RegexTest\n def initialize(str, regex)\n @str = str\n @regex = regex\n @result = str.scan(regex)\n end\n def display_details()\n puts "String = #@str"\n puts "regex = #@regex"\n puts "result = #@result"\n end\nend\n# Create Objects\nstr1 = RegexTest.new("The rain in Spain stays mainly on the plain", \/\\w+ain\/)\nstr2 = RegexTest.new("In Hertford, Hereford, and Hampshire, hurricanes hardly ever happen", \/H\\w+\/)\n# Call Methods\nstr1.display_details()\nstr2.display_details()\n<\/pre><\/div>\n\n\n\n
<\/p>\n\n\n\nresult = [\"rain\", \"Spain\", \"main\", \"plain\"]<\/code><\/p>\n\n\n\nresult = [\"Hertford\", \"Hereford\", \"Hampshire\"]<\/code>
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<\/p>\n\n\n\n
<\/p>\n\n\n\nresult = rain<\/code><\/p>\n\n\n\nresult = Hertford<\/code>
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