I know there are easier ways to get file extensions with JavaScript, but partly to practice my regexp skills I wanted to try and use a regular expression to split a filename into two strings, before and after the final dot (. character).
Here's what I have so far
const myRegex = /^((?:[^.]+(?:\.)*)+?)(\w+)?$/
const [filename1, extension1] = 'foo.baz.bing.bong'.match(myRegex);
// filename1 = 'foo.baz.bing.'
// extension1 = 'bong'
const [filename, extension] = 'one.two'.match(myRegex);
// filename2 = 'one.'
// extension2 = 'two'
const [filename, extension] = 'noextension'.match(myRegex);
// filename2 = 'noextension'
// extension2 = ''
I've tried to use negative lookahead to say 'only match a literal . if it's followed by a word that ends in, like so, by changing (?:\.)* to (?:\.(?=\w+.))*:
/^((?:[^.]+(?:\.(?=(\w+\.))))*)(\w+)$/gm
But I want to exclude that final period using just the regexp, and preferably have 'noextension' be matched in the initial group, how can I do that with just regexp?
Here is my regexp scratch file: https://regex101.com/r/RTPRNU/1
For the first capture group, you could start the match with 1 or more word characters. Then optionally repeat a . and again 1 or more word characters.
Then you can use an optional non capture group matching a . and capturing 1 or more word characters in group 2.
As the second non capture group is optional, the first repetition should be on greedy.
^(\w+(?:\.\w+)*?)(?:\.(\w+))?$
The pattern matches
^ Start of string( Capture group 1
\w+(?:\.\w+)*? Match 1+ word characters, and optionally repeat . and 1+ word characters) Close group 1(?: Non capture group to match as a whole
\.(\w+) Match a . and capture 1+ word chars in capture group 2)? Close non capture group and make it optional$ End of stringconst regex = /^(\w+(?:\.\w+)*?)(?:\.(\w+))?$/;
[
"foo.baz.bing.bong",
"one.two",
"noextension"
].forEach(s => {
const m = s.match(regex);
if (m) {
console.log(m[1]);
console.log(m[2]);
console.log("----");
}
});Another option as @Wiktor Stribiżew posted in the comments, is to use a non greedy dot to match any character for the filename:
^(.*?)(?:\.(\w+))?$
If you really want to use regex, I would suggest to use two regex:
// example with 'foo.baz.bing.bong'
const firstString = /^.+(?=\.\w+)./g // match 'foo.baz.bing.'
const secondString = /\w+$/g // match 'bong'How about something more explicit and accurate without looking around ...
named groups variant ... /^(?<noextension>\w+)$|(?<filename>\w+(?:\.\w+)*)\.(?<extension>\w+)$/
without named groups ... /^(\w+)$|(\w+(?:\.\w+)*)\.(\w+)$/
Both of the just shown variants can be shortened to 2 capture groups instead of the above variant's 3 capture groups, which in my opinion makes the regex easier to work with at the cost of being less readable ...
named groups variant ... /(?<filename>\w+(?:\.\w+)*?)(?:\.(?<extension>\w+))?$/
without named groups ... /(\w+(?:\.\w+)*?)(?:\.(\w+))?$/
const testData = [
'foo.baz.bing.bong',
'one.two',
'noextension',
];
// https://regex101.com/r/RTPRNU/5
const regXTwoNamedFileNameCaptures = /(?<filename>\w+(?:\.\w+)*?)(?:\.(?<extension>\w+))?$/;
// https://regex101.com/r/RTPRNU/4
const regXTwoFileNameCaptures = /(\w+(?:\.\w+)*?)(?:\.(\w+))?$/;
// https://regex101.com/r/RTPRNU/3
const regXThreeNamedFileNameCaptures = /^(?<noextension>\w+)$|(?<filename>\w+(?:\.\w+)*)\.(?<extension>\w+)$/
// https://regex101.com/r/RTPRNU/3
const regXThreeFileNameCaptures = /^(\w+)$|(\w+(?:\.\w+)*)\.(\w+)$/
console.log(
'based on 2 named file name captures ...\n',
testData, ' =>',
testData.map(str =>
regXTwoNamedFileNameCaptures.exec(str)?.groups ?? {}
)
);
console.log(
'based on 2 unnamed file name captures ...\n',
testData, ' =>',
testData.map(str => {
const [
match,
filename,
extension,
] = str.match(regXTwoFileNameCaptures) ?? [];
//] = regXTwoFileNameCaptures.exec(str) ?? [];
return {
filename,
extension,
}
})
);
console.log(
'based on 3 named file name captures ...\n',
testData, ' =>',
testData.map(str => {
const {
filename = '',
extension = '',
noextension = '',
} = regXThreeNamedFileNameCaptures.exec(str)?.groups ?? {};
return {
filename: filename || noextension,
extension,
}
})
);
console.log(
'based on 3 unnamed file name captures ...\n',
testData, ' =>',
testData.map(str => {
const [
match,
noextension = '',
filename = '',
extension = '',
] = str.match(regXThreeFileNameCaptures) ?? [];
//] = regXThreeFileNameCaptures.exec(str) ?? [];
return {
filename: filename || noextension,
extension,
}
})
);.as-console-wrapper { min-height: 100%!important; top: 0; }