How to build regex to match values if they exists - regex

Question

I have a requirement to match the complete string if some part of value exists or not
For example :- Here are the list of strings that should be matched
en.key.value
fr.key.value
es.key.value
pt.key.value
key.value
So, length of string before first . can only be >=2.
Below are some values which should not be accepted
.key.value
z.key.value
Could someone please help ?
Thanks in advance

Answer 1

^[^.]{2,}\..+$
Matches
en.key.value
fr.key.value
es.key.value
pt.key.value
key.value
Does not match
.key.value
z.key.value
See yourself: Regexr.com

Answer 2

You could use the following regex : /[a-z]{2,}\.[a-z]+\.[a-z]+/g
[a-z]{2,} matches 2 or more repetitions of characters in the range between a and z.
\. matches the dot character.
[a-z]+ matches 1 or more repetitions of characters between a and z.
let regex = /[a-z]{2,}\.[a-z]+\.[a-z]+/g;
console.log(regex.test("fr.key.value"));
console.log(regex.test("z.key.value"));
Regex101.

Answer 3

You don't need to use regular expressions. You can split the string on the dots and check the length of the first part.
String[] strings = {"en.key.value",
"fr.key.value",
"es.key.value",
"pt.key.value",
"key.value",
".key.value",
"z.key.value"};
for (String string : strings) {
String[] parts = string.split("\\.");
System.out.printf("[%b] %s%n", (parts[0].length() >= 2), string);
}
Above code produces following output.
[true] en.key.value
[true] fr.key.value
[true] es.key.value
[true] pt.key.value
[true] key.value
[false] .key.value
[false] z.key.value
However, if you insist on using regular expressions, consider the following.
String[] strings = {"en.key.value",
"fr.key.value",
"es.key.value",
"pt.key.value",
"key.value",
".key.value",
"z.key.value"};
Pattern pattern = Pattern.compile("^[a-z]{2,}\\.");
for (String string : strings) {
Matcher matcher = pattern.matcher(string);
System.out.printf("[%b] %s%n", matcher.find(), string);
}
Explanation of regular expression ^[a-z]{2,}\\.
^ start of string
[a-z] any lower-case letter of the English alphabet
{2,} two or more occurrences of the preceding
\\. literal dot
In other words, the above pattern matches strings that start with two or more lower-case characters followed by a single dot.