How to Check If a String Has at Least One Number in It Using Ruby

How do I check if a string has at least one number in it using Ruby?

You can use the String class's =~ method with the regex /\d/ as the argument.

Here's an example:

s = 'abc123'

if s =~ /\d/         # Calling String's =~ method.
  puts "The String #{s} has a number in it."
else
  puts "The String #{s} does not have a number in it."
end

How to check if given username has at least one letter in ruby

As I understand you want to determine if the string has only letters and numbers and at least one letter. You could use the following regular expression:

r = /\A\p{Alnum}*\p{L}\p{Alnum}*\z/

This reads, "match a start-of-string anchor, followed by zero or more alphanumeric (Unicode) characters (letters or numbers), followed by a letter, followed by zero or more alphanumeric characters, followed by an end-of-string anchor".

"12abc34".match?(r) #=> true
"1234567".match?(r) #=> false
"=12abc3".match?(r) #=> false
"".match?(r)        #=> false

Another way:

r = /\A(?=.*\p{L})\p{Alnum}*\z/

This reads, "match a start-of-string anchor, followed by a letter preceded by zero or more of characters, in a positive lookahead (which consumes no characters), followed by zero or more alphanumeric characters, followed by an end-of-string anchor".

Check if a string contains only digits in ruby

You can try the following

def check_string(string)
  string.scan(/\D/).empty?
end

It would be truthy if string contains only digits or if it is an empty string. Otherwise returns false.

Is there a nice way to check if a string contains at least one string from an array of strings?

arrays_of_strings_to_check_against.map{ |o| string_1 =~ /\b#{Regexp.escape(o)}\b/ }.any?

Or even:

arrays_of_strings_to_check_against.any?{ |o| string_1 =~ /\b#{Regexp.escape(o)}\b/ }

In Ruby, can I check if a string contains a letter without using regular expressions?

Try this

str.count("a-zA-Z") > 0

The count function accepts character sets as argument.

This might still fail with ArgumentError: invalid byte sequence in UTF-8 though. If your input is invalid there is likely no way around fixing the encoding.

NB, this scans the entire string, but so does downcase. For a performance benchmark see Eric's answer, performance varies a lot between worst case and best case scenario. As always though, readability comes before premature optimization.

Check if string has only `0` and `1`

Four ways using String methods:

str1 = '100100110'
str2 = '100100210'

String#delete

str1.delete('01') == '' #=> true
str2.delete('01') == '' #=> false

String#tr

str1.tr('01','') == '' #=> true
str2.tr('01','') == '' #=> false

String#gsub

str1.gsub(/[01]/,'') == '' #=> true
str2.gsub(/[01]/,'') == '' #=> false

String#count

str1.count('01') == str1.size #=> true
str2.count('01') == str2.size #=> false

Check if string contains only permitted characters

Using positive lookahead:

pattern = /^(?=.*\D)[-\w]+$/

pattern =~ 'qwerty'
# => 0
pattern =~ 'identifier-45'
# => 0
pattern =~ 'u_-_-'
# => 0
pattern =~ '-42-'
# => 0

pattern =~ '123456'
# => nil
pattern =~ 'w&1234'
# => nil
pattern =~ 'identifier 42'
# => nil

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