regex to remove all text before a character

Question

Is there an easy way to remove all chars before a "_"? For example, change 3.04_somename.jpg to somename.jpg.

Any suggestions for where to learn to write regex would be great too. Most places I check are hard to learn from.

In which language ? there are a few varieties of Regex you see. — Russ Clarke, Oct 17 '11 at 12:49
This is a classic http://www.regular-expressions.info/tutorial.html — xanatos, Oct 17 '11 at 12:55
first, it is not hard. and, you need to point out in which situation your problem is. — Ya Zhuang, Oct 17 '11 at 12:56
@RussC: In this case, the language isn't all that relevant because that kind of regex is so basic (and doesn't need any of those newfangled non-regular regex extensions), it'll work in more or less any regex engine, even POSIX BREs. Of course, the OP still needs to know how to apply the regex to his string, so you're still right, of course. — Tim Pietzcker, Oct 17 '11 at 13:28

score 97 · Accepted Answer · answered Oct 17 '11 at 12:51

97

^[^_]*_

will match all text up to the first underscore. Replace that with the empty string.

For example, in C#:

resultString = Regex.Replace(subjectString, 
    @"^   # Match start of string
    [^_]* # Match 0 or more characters except underscore
    _     # Match the underscore", "", RegexOptions.IgnorePatternWhitespace);

For learning regexes, take a look at http://www.regular-expressions.info

answered Oct 17 '11 at 12:51

Tim Pietzcker

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any idea how to do this in javascript? – Lukasz Oct 19 '11 at 18:36
1

The regex is exactly the same; the site I linked to contains all the info on how to do a regex replace in JavaScript. – Tim Pietzcker Oct 19 '11 at 19:08
@Lukasz - in JavaScript you do: var result = '3.04_somename.jpg'.replace(/^[^_]*_/, ''); – romiem Oct 13 '14 at 09:34
How can I extend this RegEx to go all the way till the last occurance of the '_'? – nikjohn Mar 05 '15 at 12:17
3

@ChanandlerBong: You would use a different regex for that, not extend the current one. Something like `^.*_` would be the simplest way. – Tim Pietzcker Mar 05 '15 at 13:27

score 7 · Answer 2 · answered Oct 17 '11 at 13:03

The regular expression:

^[^_]*_(.*)$

Then get the part between parenthesis. In perl:

my var = "3.04_somename.jpg";
$var =~ m/^[^_]*_(.*)$/;
my fileName = $1;

In Java:

String var = "3.04_somename.jpg";
String fileName = "";
Pattern pattern = Pattern.compile("^[^_]*_(.*)$");
Matcher matcher = pattern.matcher(var);
if (matcher.matches()) {
    fileName = matcher.group(1);
}

...

score 4 · Answer 3 · answered Oct 17 '11 at 13:05

4

no need to do a replacement. the regex will give you what u wanted directly:

"(?<=_)[^_]*\.jpg"

tested with grep:

 echo "3.04_somename.jpg"|grep -oP "(?<=_)[^_]*\.jpg"
somename.jpg

answered Oct 17 '11 at 13:05

Kent

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Just what I was looking for, thanks! I'll give these suggestions a try. Working with Perl regex here. – greenage Aug 09 '19 at 21:23

score 3 · Answer 4 · answered Oct 17 '11 at 13:01

Variant of Tim's one, good only on some implementations of Regex: ^.*?_

var subjectString = "3.04_somename.jpg";
var resultString = Regex.Replace(subjectString,
    @"^   # Match start of string
    .*?   # Lazily match any character, trying to stop when the next condition becomes true
    _     # Match the underscore", "", RegexOptions.IgnorePatternWhitespace);

score 2 · Answer 5 · answered Sep 22 '15 at 20:10

2

In Javascript I would use /.*_/, meaning: match everything until _ (including)

Example:

console.log( 'hello_world'.replace(/.*_/,'') ) // 'world'

answered Sep 22 '15 at 20:10

Fabiano Soriani

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score 1 · Answer 6 · answered Jun 23 '22 at 19:31

For Notepad++ users who are getting all but one line's results deleted, try this:

^.*_

Check the box for "Wrap around" Uncheck the box for "matches newline" Click "Replace All"

Source: https://www.winhelponline.com/blog/notepad-plus-find-and-replace-text/

score 0 · Answer 7 · answered Oct 27 '21 at 18:44

0

If you cast your url as [System.Uri], the localPath field gives you what you want:

$link_url = "https://www.subdomain.domain.com/files
$local_path= [System.Uri]::new($link_url)

Will yield $local_path = /files

answered Oct 27 '21 at 18:44

Don Koscheka

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Hidde · Answer 8 · 2011-10-17T13:10:43.607

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I learned all my Regex from this website: http://www.zytrax.com/tech/web/regex.htm. Google on 'Regex tutorials' and you'll find loads of helful articles.

String regex = "[a-zA-Z]*\.jpg";
System.out.println ("somthing.jpg".matches (regex));

returns true.

edited Oct 17 '11 at 13:10

answered Oct 17 '11 at 12:56

Hidde

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You'll want to escape the dot :) – Tim Pietzcker Oct 17 '11 at 13:03

regex to remove all text before a character

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