Swift replace occurrence of string with condition

Question

I have string like below

I am a strongPerson

I want to covert this string like this

I am a weakPerson

When I try below code

let old = "<p><strong>I am a strongPerson</strong></p>"
let new = old.replacingOccurrences(of: "strong", with: "weak")
print("\(new)")

I am getting output like

<weak>I am a weakPerson</weak>

But I need output like this

I am a weakPerson

My Condition here is

1.It has to replace only if word does not contain these HTML Tags like "<>".

Help me to get it. Thanks in advance.

@Sh_Khan Can you please kindly help me to write Regular Expression? — Mani murugan
– Mani murugan, Commented Jun 20, 2019 at 16:40

rmaddy · Accepted Answer · 2019-06-20 16:45:01Z

4

You can use a regular expression to avoid the word being in a tag:

let old = "strong <p><strong>I am a strong person</strong></p> strong"
let new = old.replacingOccurrences(of: "strong(?!>)", with: "weak", options: .regularExpression, range: nil)
print(new)

I added some extra uses of the word "strong" to test edge cases.

The trick is the use of (?!>) which basically means to ignore any match that has a > at the end of it. Look at the documentation for NSRegularExpression and find the documentation for the "negative look-ahead assertion".

Output:

weak I am a weak person weak

answered Jun 20, 2019 at 16:45

rmaddy

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5 Comments

Sam Over a year ago

I recommend that you also use a negative look-behind to avoid matching "strong>", so the regular expression would then be "(?<!<|<\/)strong(?!>)". A link to explain this is here: regexr.com/4g5o4

rmaddy Over a year ago

@Sam I was assuming you would never find strong> in the string because the > would be entered as >.

Mani murugan Over a year ago

@Sam It shows error for this string "\" , Invalid escape sequence in literal

rmaddy Over a year ago

In a Swift string you would need "(?<!<|<\\/)string(?!>)". Note the double backslash.

Sam Over a year ago

@Manimurugan Exactly

Falyoun · Accepted Answer · 2019-06-20 17:03:24Z

1

Try the following:

let myString = "<p><strong>I am a strongPerson</strong></p>"
if let regex = try? NSRegularExpression(pattern: "strong(?!>)") {

 let modString = regex.stringByReplacingMatches(in: myString, options: [], range: NSRange(location: 0, length:  myString.count), withTemplate: "weak")
  print(modString)
}

edited Jun 20, 2019 at 17:03

answered Jun 20, 2019 at 16:47

Falyoun

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4 Comments

rmaddy Over a year ago

Why case insensitive?

Falyoun Over a year ago

In case of I am a StrongPerson, As well as i have it in one of my file so he can omit it

rmaddy Over a year ago

But then StrongPerson becomes weakPerson and not WeakPerson. That may or may not be what the OP wants.

Falyoun Over a year ago

Thanks for your note, I'll omit it

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