ruby regular expression to see if only numbers - ruby

I'd like to have a reqex that checks that every character is a number [0-9]+. I have tried:
'4th'=~/[\d]+/
'4th'=~/\d+/
but not working. How would I check for this?
thx


"12345" =~ /\A\d+\Z/
\A = beginning of string (not line, string)
\d+ = one or more digits
\Z = end of string (not line, string)


The simplest way is:
str !~ /\D/

Related

How to create reqular expression to match number at the absolute end of text (without "\n")

Example code:
test = "123knh8y78hah099ajs980"
test.scan(/\d+\Z/)
As a result, I should get:
=> ["980"]
It is correct. But if add the "\n" to the end of the text, regexp return
incorrect result:
test = "123knh8y78hah099ajs980\n"
test.scan(/\d+\Z/)
=> ["980"]
Nothing changed, but the number is not the end of text. In the end of text symbol "\n".
Hot to create reqular expression to fix this problem?

You need to replace \Z with \z if you do not need to match 980 at the end of the string or before the final \n (which is matched with \Z).
See Ruby Regex reference:
\Z - Matches end of string. If string ends with a newline, it matches just before newline
\z - Matches end of string

Find the first index of a non-numeric character

Suppose I have a String:
someString = "1374j03d42s23dc"
I want to find the first index of a non-numeric character. In this case, that would be 4. How can I do this with a regex?
(I'm not very good at regex, so it would be great if the answer could explain what is going on)

someString =~ /\D/
# => 4
........

In addition to sawa's solution: You could also use String#index when you like your code to be more readable:
string = '1374j03d42s23dc'
string.index(/\D/)
#=> 4
/\D/ matches any non-digit (list of common regexp metacharacters)

Try:
someString.each_char.with_index { |c,i| puts i if c == someString.scan(/\D+/)[0] }

regex scan only returning first value

I have two strings that should both return matches according to the regex, but only str1 returns the expected match. str1 is an exact match for the regex (created by Avinash Raj) below. str2 contains str1 and more data. I expected str2 to return str1 and more values that matched, but it returns nothing Can someone explain why?
str1="3,15,14,31,40,5,5,4,5,3,4,4,5,2,2,2,1,2,1,1,3,3,3,2,4,3,false,false,false,false,false,true,false,true,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,3,3,3,2,3"
str2="3,15,14,31,40,5,5,4,5,3,4,4,5,2,2,2,1,2,1,1,3,3,3,2,4,3,false,false,false,false,false,true,false,true,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,3,3,3,2,3,3,15,14,35,27,4,5,3,5,3,2,4,4,2,1,1,2,2,2,1,3,3,3,2,5,9,true,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,true,true,false,false,false,false,2,2,3,2,3,3,15,16,34,53,4,4,4,3,1,3,4,3,1,1,1,1,1,1,1,2,3,2,3,5,1,true,false,false,false,false,false,true,false,false,false,false,false,false,false,true,true,false,false,false,false,false,false,false,false,false,false,false,3,2,3,2,3,3,15,18,37,29,4,4,4,3,2,3,3,4,1,1,1,1,1,1,1,1,3,1,2,4,1,true,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,3,2,3,2,3,3,15,20,34,37,4,4,4,3,1,3,3,4,1,1,1,1,1,1,1,1,1,1,2,4,1,false,false,false,true,false,false,false,false,false,false,false,false,false,true,false,true,false,false,false,false,false,false,false,false,true,false,false,3,1,3,1,3,3,16,10,18,30,4,3,3,3,1,3,3,3,1,1,1,1,1,1,1,1,2,1,4,4,3,false,false,false,false,false,true,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,3,2,3,2,3,3,16,12,39,5,5,5,4,5,3,5,5,5,1,1,1,1,1,1,1,2,1,1,1,5,10,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,3,2,3,2,3,3,16,14,18,27,4,4,4,4,2,3,3,4,1,1,1,1,1,1,1,1,1,1,2,5,1,true,false,false,false,false,false,false,false,false,false,false,false,false,true,false,true,false,false,false,false,true,false,false,false,false,false,false,3,2,3,2,3,3,16,16,18,32,5,5,5,5,4,5,5,5,1,1,1,1,1,1,1,2,1,1,1,5,3,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,true,false,3,2,3,2,3,3,16,18,20,7,5,5,5,5,3,3,3,4,1,1,1,1,1,1,1,1,1,1,2,5,1,false,false,false,true,false,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,true,false,false,false,false,false,false,3,2,3,2,3,3,16,20,18,59,4,4,4,3,1,1,1,2,1,1,1,1,1,1,1,1,2,2,4,5,9,false,false,false,true,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,3,2,3,2,3,3,17,10,16,9,3,3,3,3,1,2,3,3,1,1,1,1,1,1,1,1,2,1,3,5,1,true,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,3,2,3,2,3,3,17,12,16,17,4,3,4,2,1,4,3,2,1,1,1,1,1,1,1,1,1,1,4,5,3,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,3,2,3,2,3,3,17,14,16,21,4,4,4,4,1,3,4,4,1,1,1,1,1,1,1,1,1,1,2,5,1,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,true,false,false,3,2,3,2,3,3,17,16,16,20,5,5,4,5,3,4,4,5,1,1,1,1,1,1,1,1,1,1,1,5,8,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,true,false,false,false,3,2,3,2,3,3,17,18,16,31,4,4,4,4,1,4,3,3,1,1,1,1,1,1,1,1,1,1,3,5,1,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,true,false,true,false,false,false,false,3,2,3,2,3,3,17,20,18,8,5,5,4,5,4,4,4,5,1,1,1,1,1,1,1,2,1,1,1,5,1,false,false,false,true,false,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,true,false,false,false,3,2,3,2,3,3,18,10,31,33,3,2,3,2,2,2,2,3,1,1,1,1,1,1,1,1,1,1,1,5,7,true,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,3,2,3,2,3,3,18,12,36,11,4,4,4,5,3,4,3,3,1,1,2,1,2,1,2,2,1,1,1,5,1,false,false,false,true,false,false,true,false,false,false,false,false,false,true,false,true,false,false,false,false,false,false,false,false,true,false,false,3,2,3,2,3,3,18,14,49,6,3,3,2,2,1,2,2,2,2,1,1,1,2,1,2,3,3,4,4,5,9,true,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,3,2,3,2,3,3,18,16,32,53,3,4,4,3,3,3,3,3,1,1,1,1,1,1,2,2,1,1,3,5,7,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,true,false,false,false,false,3,2,3,2,3,3,18,18,37,59,5,4,4,4,4,4,4,4,1,1,1,1,1,1,1,2,1,1,2,5,7,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,true,false,false,false,false,3,2,3,2,3,3,19,10,5,25,4,4,4,2,2,4,3,3,1,1,1,1,1,1,1,1,2,2,2,5,1,true,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,2,1,3,2,3,3,19,13,0,5,5,5,4,5,3,3,5,5,1,1,1,1,1,1,1,1,1,1,3,5,7,false,false,true,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,false,false,true,false,false,false,false,false,false,3,2,3,2,3,3,19,14,5,23,4,4,4,4,3,4,3,3,1,1,1,1,1,1,1,1,1,2,2,5,9,false,false,true,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,false,3,2,3,2,3,3,19,16,7,19,5,4,4,4,3,4,3,3,1,1,1,1,1,1,1,2,2,2,3,5,9,false,false,true,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,3,2,3,2,3,3,19,18,6,30,4,4,4,4,3,4,4,4,1,1,1,1,1,1,1,1,1,1,1,5,8,false,false,true,true,false,false,false,false,false,false,false,false,false,false,false,false,false,false,true,false,true,false,false,false,true,false,false,3,2,3,2,3,3,19,20,8,25,4,4,5,4,3,4,3,4,1,1,1,1,1,1,1,1,1,1,3,5,1,false,false,true,false,false,false,true,false,false,false,false,false,false,true,false,false,false,false,false,false,false,false,false,false,true,false,false,3,2,3,2,3,3,19,21,18,2,4,4,4,3,3,4,3,4,1,1,1,1,1,1,1,1,1,1,1,5,1,false,false,true,false,false,false,false,false,false,false,false,false,false,true,false,false,false,false,true,false,true,false,false,false,true,false,false,3,2,3,2,3,"
str1.scan(/^,?(?:[1-5]\d|[1-9])(?:,(?:[1-5]\d|[1-9])){4}(?:,[1-5]){21}(?:,(?:true|false)){27}(?:,[1-5]){5}$/).each{|x|
puts x
puts "---1---"
}
str2.scan(/^,?(?:[1-5]\d|[1-9])(?:,(?:[1-5]\d|[1-9])){4}(?:,[1-5]){21}(?:,(?:true|false)){27}(?:,[1-5]){5}$/).each{|x|
puts x
puts "---2---"
}

Kind of by definition, you can't have more than one pattern match in a string when your pattern specifically says "start of string, then [stuff], then end of string". Look at regexp anchors ^ and $.
A simpler example might make it clearer: ^a$ "start of string, then letter a, then end of string" will match in "a" once, but will match in "aaa" zero times, even though there are three letters a.

$ assert position at end of a line
Now you are not matching upto the end of line.
^,?(?:[1-5]\d|[1-9])(?:,(?:[1-5]\d|[1-9])){4}(?:,[1-5]){21}(?:,(?:true|false)){27}(?:,[1-5]){5}
Just remove the $ from the end.See demo.
https://regex101.com/r/sJ9gM7/22

Because you're regular starts with the ^ metacharacter and ends with the $ metacharacter, it expects the full string to match.

remove both commas and white space ruby

I am new to ruby and my regex knowledge leaves a lot to be desired. I am trying to check if a string is a palindrome, but wish to ignore white space and commas.
The current code I have is
def palindrome(string)
string = string.downcase
string = string.gsub(/\d+(,)\d+//\s/ ,"")
if string.reverse == string
return true
else
return false
end
end
Any assistance here would be greatly appreciated.

but wish to ignore white space and commas
You don't need to put \d in your regex. Just replace the spaces or commas with empty string.
string = string.gsub(/[\s,]/ ,"")
The above gsub command would remove all the spaces or commas. [\s,] character class which matches a space or comma.

Another way would be to use the method String#tr:
str = "pat, \t \ntap"
str.tr(" ,\t\n", '') #=> "pattap"

Regex condition on first and last characters

How can I write a regex to match a string that does not start or end with a white space character? A matching string can have any character in the middle, and importantly, a single-character string should match.
My attempt was:
/\A\S.*\S\z/
but this will not match a single character.

This is one of the cases where you should not attempt to build a regex that matches something, but rather a regex that matches the complement of something, and use the regex negatively.
re = /\A\s|\s\z/
re !~ " " # => false
re !~ "" # => true
re !~ "sss" # => true
re !~ "s ss" # => true
re !~ " s ss" # => false

is_ok = lambda do |str|
a, z = str.chars.first, str.chars.last
"#{a}#{z}" =~ / |\n|\t/ ? false : true
end
#"more elegant" (yeah dude I rock)
is_ok = lambda {|str| [0, -1].map{|i| str.chars[i] }.join =~ / |\n|\t/ ? false : true}

Use this regex:
\A\S+(?:\s*\S+)*\Z
You can play with the Test String part of this demo to see how this works. I'm assuming that strings can span multiple lines, hence the \A and \Z
In Ruby, something like:
if subject =~ /\A\S+(?:\s*\S+)*\Z/
match = $&
Explanation
The \A anchor asserts that we are at the beginning of the subject string
\S+ matches one or more non-whitespace characters (including tabs, newlines etc.) Alternaltely, if you want to allow newlines at the beginning but only want to exclude a space character, you can use [^ ]+ instead of \S+
(?:\s*\S+) matches any number of optional whitespace characters, followed by one or more non-space characters
The * quantifier repeats that zero or more times
The \Z anchor asserts that we are at the end of the subject string

Use lookaheads, like this:
\A(?=\S).*\S\Z
Regex101 Demo
This matches the start of the string and requires (1) that the first character be a non-whitespace character and (2) that the last character be a non-whitespace character.
Matches:
a
a b
a b c d 1231 e
Non matches:
(just a space)
a (leading space)
b (trailing space)
empty string

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