Regular expression to get a match or replace a subString

Question

I need to match or replace a part of string like below, but I couldn't write the exact regular expression for that in java.

String:

text1${text2${text3}text4}text5

Expected regex should match the test3 alone, ie. anything inside "inner" ${}. Above example has an outer ${...} and an inner ${...}, like ...${...${...}...}.... And test3 is inside the "inner ${} which is what I want.

The following regex captures the entire content within ${...}, not just the content of "inner" ${...}

\$\{(.*?)\}

More Examples:

text1${text2${text3}text4}text5 - match "text3"
text1text2${text3}text4text5    - should not match anything
text1${text2${text3}text4text5  - should not match anything

Update:

text1${text2${text3}${text4}text5} - match "text3" and "text4"

Give several examples of input, and for each input, show the desired output for that input. — David Choweller
– David Choweller, Commented Feb 4, 2017 at 0:08

Wiktor Stribiżew · Accepted Answer · 2017-02-04 00:08:45Z

2

The . matches both { and }. You need to exclude matching { and }:

\$\{([^{}]*)}
     ^^^^^

See the regex demo. The [^{}]* is a negated character class matching 0+ chars other than { and }.

Java code:

String str = "text1${text2${text3}text4}text5";
Pattern p = Pattern.compile("\\$\\{([^{}]*)}");
Matcher m = p.matcher(str);
while (m.find()) {
    System.out.println(m.group(1));
}
// => text3

answered Feb 4, 2017 at 0:08

Wiktor Stribiżew

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2 Comments

user3366706 Over a year ago

this one matches even with single ${...} like if string is "text1${text2}text3" then text2 matches your regex. but it would be nice if I can get only that matches "inner" ${}, so "text1${text2}text3" should not have anything matching, but string like this "text1${text2${text3}}" should match the inner text3 substring

Wiktor Stribiżew Over a year ago

Try "\\$\\{[^{}]*\\$\\{([^{}]*)}[^{}]*}" regex.

Shakiba Moshiri · Accepted Answer · 2017-02-07 21:07:22Z

0

First you need to match the entire between the first { and the last } and after that you can match what you want by using match-group.

what you want
{.*\{(.*?)\}.*?\}

In the first step it match {text2${text3} and after that you should use math-group

I am not familiar with Java but I know a little with Perl and C++ and I think it works in Java because it is easy and not complex

demo

Test with Perl

echo 'text1${text2${text3}text4}text5' | perl -lne '/\{.*\{(.*?)\}.*?\}/ && print $1'

output

text3

So in you Java code use $1 that's it.

For your update that you wrote, you have 2 choices one with a loop over your string and other with four match-group

First with a while loop
echo 'text1${text2${text3}${text4}text5}' | perl -lne 'print $2 while /(\${)(\w+)(\$?})/g'
text3
text4
How does it work? very easy. It first match ${text3} and here \w+ would be text3 then it goes ahead and match ${text4} and again \w+ would be text4
(\${)(\w+)(\$?})
prove

Second with non-loop
echo 'your-string' | perl -lne ' /(\${)(\w+)(\$?})\1(\w+)\3/g && print $2," ",$4'

This one also easy. It first matches text3 and then matches text4 and puts them in $2 and $4. that's it.
(\${)(\w+)(\$?})\1(\w+)\3
prove

NOTE
With while loop you need to use g flag and you can not ignore it but for second no problem.
Again

edited Feb 7, 2017 at 21:07

answered Feb 6, 2017 at 20:15

Shakiba Moshiri

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2 Comments

user3366706 Over a year ago

with slight modification it works for what I wanted \${.*\$\{(.*?)\}.*?\} There is a slight improvement I need from this regex. For example: in this string text1${text2${that}text4${this}text5} it captures only 'this', ie. only one inner substring. I could not make it to capture all matching substring in one go, ie. capture 'this', and 'that' in one go.

Shakiba Moshiri Over a year ago

@user3366706 your ask does not make sense to me. You should know that regexes are very sensitive and I wrote this for your purpose that you wrote above. If you want a thing for both or anything just update your question. Also this text1${text2${that}text4${this}text5} is difference from one you have written. So think and exactly tell what you want.

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