Interpolating a string into a regex

Chris_Bunch_422 0
Viewed 57130

I need to substitute the value of a string into my regular expression in Ruby. Is there an easy way to do this? For example:

foo = "0.0.0.0"
goo = "here is some other stuff 0.0.0.0" 
if goo =~ /value of foo here dynamically/
  puts "success!"
end
ruby regex
7 Answers

Same as string insertion.

if goo =~ /#{Regexp.quote(foo)}/
#...
Jonathan_Lonowski_150310

Note that the Regexp.quote in Jon L.'s answer is important!

if goo =~ /#{Regexp.quote(foo)}/

If you just do the "obvious" version:

if goo =~ /#{foo}/

then the periods in your match text are treated as regexp wildcards, and "0.0.0.0" will match "0a0b0c0".

Note also that if you really just want to check for a substring match, you can simply do

if goo.include?(foo)

which doesn't require an additional quoting or worrying about special characters.

glenn_mcdonald_79190

Probably Regexp.escape(foo) would be a starting point, but is there a good reason you can't use the more conventional expression-interpolation: "my stuff #{mysubstitutionvariable}"?

Also, you can just use !goo.match(foo).nil? with a literal string.

Truesdell_134330 
Regexp.compile(Regexp.escape(foo))
MizardX_223640

Use Regexp.new:

if goo =~ Regexp.new(foo) # Evaluates to /0.0.0.0/
Jeremy_Ruten_8130 
foo = "0.0.0.0"
goo = "here is some other stuff 0.0.0.0" 

puts "success!" if goo =~ /#{foo}/
Mike_Breen_223460
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