replace specific word using regex except one case

Question

i have three string app, app_abc, appabc i want to replace any of the string with code (for replacing) output should be

app -> code,

app_abc -> code_abc,

appabc -> appabc

i have tried this replaceAll("^app", code); but it will be replaced starting app

wrong output:

app -> code,

app_abc -> code_abc,

appabc -> codeabc(i want to exclude this type of string using regex)

i know i have to use or oprator so i have tried this

replaceAll("^app|app_(?!(.*))", code);

https://regex101.com/r/Ils9kM/1

but it is wrong i think anyone can suggest ?

You don't have to use an alternation (the OR operator) nor a lookahead. You need an optional capturing group and word boundaries. — Casimir et Hippolyte
– Casimir et Hippolyte, Commented Feb 18, 2017 at 12:44
Negative lookahead to the rescue: replaceAll("^app(?!abc)", "code") — Alex Shesterov
– Alex Shesterov, Commented Feb 18, 2017 at 12:50
Can we say that you want to replace app when it is at the beginning of a string but not followed by any letter? — Niitaku
– Niitaku, Commented Feb 18, 2017 at 12:56
I'd advise replaceAll("\\bapp(?![a-zA-Z])", "code"); or the pattern can also be "\\bapp(?=\\b|_)" — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Feb 18, 2017 at 12:57

Wiktor Stribiżew · Accepted Answer · 2017-02-18 13:09:51Z

2

You want to replace abc only at the start of a word and only when it is not followed with another letter. Use

replaceAll("\\bapp(?![a-zA-Z])", "code")

If you want abc to be followed with a word boundary or underscore, the pattern can also be

"\\bapp(?=\\b|_)"

answered Feb 18, 2017 at 13:09

Wiktor Stribiżew

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2 Comments

Grzegorz Górkiewicz Over a year ago

Do you recommend any in-depth Java tutorials on regexes?

Wiktor Stribiżew Over a year ago

Since I'm on a mobile right now, I cannot add more details.@Grzegorz, sorry, I do not know specific Java related regex tutorials, there is regexone.com for JavaScript. A lot can be found at regular-expressions.info.

JSS · Accepted Answer · 2017-02-18 13:17:01Z

0

Try this:

public static void main(String []args){
        Assert.assertEquals("code", repl("app"));
        Assert.assertEquals("code_abc",repl("app_abc"));
        Assert.assertEquals("appabc",repl("appabc"));
        Assert.assertEquals("appa_bc",repl("appa_bc"));
        Assert.assertEquals("fooapp",repl("fooapp"));
        Assert.assertEquals("foo_app",repl("foo_app"));
        System.out.println("All Good");
    }

    private static String repl(final String str) {
        return str.replaceAll("\\bapp(?![a-zA-Z])", "code");
    }

answered Feb 18, 2017 at 13:17

JSS

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