Ruby gsub不替换换行符

Question

I have this code

str = @universal_claim_form.errors.full_messages.join
        str.gsub('Patient Contact Information: Value', 'Patient phone number') if str =~ /Patient Contact Information/
        debugger
        str.gsub("\\n", "<br/>")
        debugger
        flash.now[:error] = "Form has errors and was unable to be submitted.<br/> " << str

the first gsub replaces an unwanted message and the second gsub it meant to replace all the newline characters with html line breaks

at the first debugger line str = "PMP Validation failed. This happens when something you entered does not pass PMP specific validations.\\\\nPatient phone number: Value must be a 10 digit number"

and at the second debugger the line hasn't changed

what's even more weird is that I did this in irb at the command line and it worked

2.1.1 :001 > s = 'test'
 => "test"
2.1.1 :002 > s
 => "test"
2.1.1 :003 > s += '\ntest'
 => "test\\ntest"
2.1.1 :004 > s.gsub('\\n', '<br/>')
 => "test<br/>test"
2.1.1 :005 >

Answer 1

You can call gsub! to mutate the string you are calling it on (instead of returning a new string).

The reason gsub "works" in irb is because it is outputting the result - irb does not do any assignment or mutation (beyond what one enters), eg

irb(main):001:0> foo = 4
=> 4
irb(main):002:0> foo + 6
=> 10

foo is getting assigned 4 so it outputs the result of that assignment, likewise with foo + 6 it outputs the result but the value of foo is unchanged.

When you call gsub it returns a new string with the substitution(s), this is why you feel it "works" in irb (this is no different then it printing "4" above).