Convert a string to regular expression ruby

Question

I need to convert string like "/[\w\s]+/" to regular expression.

"/[\w\s]+/" => /[\w\s]+/

I tried using different Regexp methods like:

Regexp.new("/[\w\s]+/") => /\/[w ]+\//, similarly Regexp.compile and Regexp.escape. But none of them returns as I expected.

Further more I tried removing backslashes:

Regexp.new("[\w\s]+") => /[w ]+/ But not have a luck.

Then I tried to do it simple:

str = "[\w\s]+"
=> "[w ]+"

It escapes. Now how could string remains as it is and convert to a regexp object?

score 177 · Accepted Answer · answered Dec 28 '11 at 06:55

177

Looks like here you need the initial string to be in single quotes (refer this page)

>> str = '[\w\s]+'
 => "[\\w\\s]+" 
>> Regexp.new str
 => /[\w\s]+/

answered Dec 28 '11 at 06:55

alony

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or you use 2 backslashes "[\\w\\s]+" – frostymarvelous Aug 07 '23 at 04:20

score 151 · Answer 2 · edited Jul 30 '16 at 09:42

151

To be clear

  /#{Regexp.quote(your_string_variable)}/

is working too

edit: wrapped your_string_variable in Regexp.quote, for correctness.

edited Jul 30 '16 at 09:42

deprecated

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answered Jul 25 '12 at 10:19

Sergey Gerasimov

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Just found out that you _can't_ append options that way, like `/#{your_regex}/#{options}`. – pdu May 15 '14 at 10:49
I suppose that you're talking about Rails? `options` is a Hash, and Ruby is not soooo dynamic =) – Sergey Gerasimov May 15 '14 at 11:54
2

This doesn't do what OP is asking on Ruby 2.1, it converts "[\w\s]+" => /[w ]+/ – Luca Spiller Nov 05 '15 at 12:16
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Please note that answer was given in 2012 year :) At that time everything was perfect – Sergey Gerasimov Nov 12 '15 at 14:38
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It was a perfect year. – Naftuli Kay Mar 10 '16 at 20:55
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Combining the answers can avoid string interpolation: Regexp.new(Regexp.quote(your_string_variable)) – Ekkstein Nov 24 '19 at 23:44

sandstrom · Answer 3 · 2015-12-27T15:46:34.337

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This method will safely escape all characters with special meaning:

/#{Regexp.quote(your_string)}/

For example, . will be escaped, since it's otherwise interpreted as 'any character'.

Remember to use a single-quoted string unless you want regular string interpolation to kick in, where backslash has a special meaning.

edited Dec 27 '15 at 15:46

answered Mar 06 '14 at 20:33

sandstrom

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Nice because it explains how we can protect the string variable that may contain signs (such as `+.`) that would be interpreted in the Regexp. – Romain Champourlier May 23 '14 at 16:39
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This doesn't do what OP is asking on Ruby 2.1, it converts "[\w\s]+" => /\[w\ \]\+/ – Luca Spiller Nov 05 '15 at 12:15
@LucaSpiller you need to use a single-quoted string, backslash is treated as a special character in double-quoted strings, which is why e.g. `"\n"` is a newline but `'\n'` isn't. – sandstrom Dec 27 '15 at 15:47

BitOfUniverse · Answer 4 · 2015-11-06T17:29:16.967

10

Using % notation:

%r{\w+}m => /\w+/m

or

regex_string = '\W+'
%r[#{regex_string}]

From help:

%r[ ] Interpolated Regexp (flags can appear after the closing delimiter)

edited Nov 06 '15 at 17:29

answered Dec 15 '14 at 11:39

BitOfUniverse

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This doesn't do what OP is asking on Ruby 2.1, it converts "[\w\s]+" => /[ws]+/ – Luca Spiller Nov 05 '15 at 12:13
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@Luca Spiller, thanks, single quotes should be used there, I'll update answer. – BitOfUniverse Nov 06 '15 at 17:29

score 7 · Answer 5 · answered Sep 17 '15 at 11:20

The gem to_regexp can do the work.

"/[\w\s]+/".to_regexp => /[\w\s]+/

You also can use the modifier:

'/foo/i'.to_regexp => /foo/i

Finally, you can be more lazy using :detect

'foo'.to_regexp(detect: true)     #=> /foo/
'foo\b'.to_regexp(detect: true)   #=> %r{foo\\b}
'/foo\b/'.to_regexp(detect: true) #=> %r{foo\b}
'foo\b/'.to_regexp(detect: true)  #=> %r{foo\\b/}

Joseph · Answer 6 · 2022-04-25T14:12:05.903

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I just ran into this, where I literally need to change the string '/[\w\s]+/' to a regex in a transpiler. I used eval:

irb(main):001:0> eval( '/[\w\s]+/' )
=> /[\w\s]+/

edited Apr 25 '22 at 14:12

answered Apr 25 '22 at 14:03

Joseph

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Convert a string to regular expression ruby

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