Develop Reference

How to parse string using regex

I'm pretty new to java, trying to find a way to do this better. Potentially using a regex.
String text = test.get(i).toString()
// text looks like this in string form:
// EnumOption[enumId=test,id=machine]
String checker = text.replace("[","").replace("]","").split(",")[1].split("=")[1];
// checker becomes machine
My goal is to parse that text string and just return back machine. Which is what I did in the code above.
But that looks ugly. I was wondering what kinda regex can be used here to make this a little better? Or maybe another suggestion?

Use a regex' lookbehind:
(?<=\bid=)[^],]*
See Regex101.
(?<= ) // Start matching only after what matches inside
\bid= // Match "\bid=" (= word boundary then "id="),
[^],]* // Match and keep the longest sequence without any ']' or ','
In Java, use it like this:
import java.util.regex.*;
class Main {
public static void main(String[] args) {
Pattern pattern = Pattern.compile("(?<=\\bid=)[^],]*");
Matcher matcher = pattern.matcher("EnumOption[enumId=test,id=machine]");
if (matcher.find()) {
System.out.println(matcher.group(0));
}
}
}
This results in
machine

Assuming you’re using the Polarion ALM API, you should use the EnumOption’s getId method instead of deparsing and re-parsing the value via a string:
String id = test.get(i).getId();

Using the replace and split functions don't take the structure of the data into account.
If you want to use a regex, you can just use a capturing group without any lookarounds, where enum can be any value except a ] and comma, and id can be any value except ].
The value of id will be in capture group 1.
\bEnumOption\[enumId=[^=,\]]+,id=([^\]]+)\]
Explanation
\bEnumOption Match EnumOption preceded by a word boundary
\[enumId= Match [enumId=
[^=,\]]+, Match 1+ times any char except = , and ]
id= Match literally
( Capture group 1
[^\]]+ Match 1+ times any char except ]
)\]
Regex demo | Java demo
Pattern pattern = Pattern.compile("\\bEnumOption\\[enumId=[^=,\\]]+,id=([^\\]]+)\\]");
Matcher matcher = pattern.matcher("EnumOption[enumId=test,id=machine]");
if (matcher.find()) {
System.out.println(matcher.group(1));
}
Output
machine
If there can be more comma separated values, you could also only match id making use of negated character classes [^][]* before and after matching id to stay inside the square bracket boundaries.
\bEnumOption\[[^][]*\bid=([^,\]]+)[^][]*\]
In Java
String regex = "\\bEnumOption\\[[^][]*\\bid=([^,\\]]+)[^][]*\\]";
Regex demo

A regex can of course be used, but sometimes is less performant, less readable and more bug-prone.
I would advise you not use any regex that you did not come up with yourself, or at least understand completely.
PS: I think your solution is actually quite readable.
Here's another non-regex version:
String text = "EnumOption[enumId=test,id=machine]";
text = text.substring(text.lastIndexOf('=') + 1);
text = text.substring(0, text.length() - 1);
Not doing you a favor, but the downvote hurt, so here you go:
String input = "EnumOption[enumId=test,id=machine]";
Matcher matcher = Pattern.compile("EnumOption\\[enumId=(.+),id=(.+)\\]").matcher(input);
if(!matcher.matches()) {
throw new RuntimeException("unexpected input: " + input);
}
System.out.println("enumId: " + matcher.group(1));
System.out.println("id: " + matcher.group(2));

What is the Regex for decimal numbers in Java?

I am not quite sure of what is the correct regex for the period in Java. Here are some of my attempts. Sadly, they all meant any character.
String regex = "[0-9]*[.]?[0-9]*";
String regex = "[0-9]*['.']?[0-9]*";
String regex = "[0-9]*["."]?[0-9]*";
String regex = "[0-9]*[\.]?[0-9]*";
String regex = "[0-9]*[\\.]?[0-9]*";
String regex = "[0-9]*.?[0-9]*";
String regex = "[0-9]*\.?[0-9]*";
String regex = "[0-9]*\\.?[0-9]*";
But what I want is the actual "." character itself. Anyone have an idea?
What I'm trying to do actually is to write out the regex for a non-negative real number (decimals allowed). So the possibilities are: 12.2, 3.7, 2., 0.3, .89, 19
String regex = "[0-9]*['.']?[0-9]*";
Pattern pattern = Pattern.compile(regex);
String x = "5p4";
Matcher matcher = pattern.matcher(x);
System.out.println(matcher.find());
The last line is supposed to print false but prints true anyway. I think my regex is wrong though.

Update
To match non negative decimal number you need this regex:
^\d*\.\d+|\d+\.\d*$
or in java syntax : "^\\d*\\.\\d+|\\d+\\.\\d*$"
String regex = "^\\d*\\.\\d+|\\d+\\.\\d*$"
String string = "123.43253";
if(string.matches(regex))
System.out.println("true");
else
System.out.println("false");
Explanation for your original regex attempts:
[0-9]*\.?[0-9]*
with java escape it becomes :
"[0-9]*\\.?[0-9]*";
if you need to make the dot as mandatory you remove the ? mark:
[0-9]*\.[0-9]*
but this will accept just a dot without any number as well... So, if you want the validation to consider number as mandatory you use + ( which means one or more) instead of *(which means zero or more). That case it becomes:
[0-9]+\.[0-9]+

If you on Kotlin, use ktx:
fun String.findDecimalDigits() =
Pattern.compile("^[0-9]*\\.?[0-9]*").matcher(this).run { if (find()) group() else "" }!!

Your initial understanding was probably right, but you were being thrown because when using matcher.find(), your regex will find the first valid match within the string, and all of your examples would match a zero-length string.
I would suggest "^([0-9]+\\.?[0-9]*|\\.[0-9]+)$"

There are actually 2 ways to match a literal .. One is using backslash-escaping like you do there \\., and the other way is to enclose it inside a character class or the square brackets like [.]. Most of the special characters become literal characters inside the square brackets including .. So use \\. shows your intention clearer than [.] if all you want is to match a literal dot .. Use [] if you need to match multiple things which represents match this or that for example this regex [\\d.] means match a single digit or a literal dot

I have tested all the cases.
public static boolean isDecimal(String input) {
return Pattern.matches("^[-+]?\\d*[.]?\\d+|^[-+]?\\d+[.]?\\d*", input);
}

Regular expression matching "dictionary words"

I'm a Java user but I'm new to regular expressions.
I just want to have a tiny expression that, given a word (we assume that the string is only one word), answers with a boolean, telling if the word is valid or not.
An example... I want to catch all words that is plausible to be in a dictionary... So, i just want words with chars from a-z A-Z, an hyphen (for example: man-in-the-middle) and an apostrophe (like I'll or Tiffany's).
Valid words:
"food"
"RocKet"
"man-in-the-middle"
"kahsdkjhsakdhakjsd"
"JESUS", etc.
Non-valid words:
"gipsy76"
"www.google.com"
"me#gmail.com"
"745474"
"+-x/", etc.
I use this code, but it won't gave the correct answer:
Pattern p = Pattern.compile("[A-Za-z&-&']");
Matcher m = p.matcher(s);
System.out.println(m.matches());
What's wrong with my regex?

Add a + after the expression to say "one or more of those characters":
Escape the hyphen with \ (or put it last).
Remove those & characters:
Here's the code:
Pattern p = Pattern.compile("[A-Za-z'-]+");
Matcher m = p.matcher(s);
System.out.println(m.matches());
Complete test:
String[] ok = {"food","RocKet","man-in-the-middle","kahsdkjhsakdhakjsd","JESUS"};
String[] notOk = {"gipsy76", "www.google.com", "me#gmail.com", "745474","+-x/" };
Pattern p = Pattern.compile("[A-Za-z'-]+");
for (String shouldMatch : ok)
if (!p.matcher(shouldMatch).matches())
System.out.println("Error on: " + shouldMatch);
for (String shouldNotMatch : notOk)
if (p.matcher(shouldNotMatch).matches())
System.out.println("Error on: " + shouldNotMatch);
(Produces no output.)

This should work:
"[A-Za-z'-]+"

But "-word" and "word-" are not valid. So you can uses this pattern:
WORD_EXP = "^[A-Za-z]+(-[A-Za-z]+)*$"

Regex - /^([a-zA-Z]*('|-)?[a-zA-Z]+)*/
You can use above regex if you don't want successive "'" or "-".
It will give you accurate matching your text.
It accepts
man-in-the-middle
asd'asdasd'asd
It rejects following string
man--in--midle
asdasd''asd

Hi Aloob please check with this, Bit lengthy, might be having shorter version of this, Still...
[A-z]*||[[A-z]*[-]*]*||[[A-z]*[-]*[']*]*

Extract an ISBN with regex

I have an extremely long string that I want to parse for a numeric value that occurs after the substring "ISBN". However, this grouping of 13 digits can be arranged differently via the "-" character. Examples: (these are all valid ISBNs) 123-456-789-123-4, OR 1-2-3-4-5-67891234, OR 12-34-56-78-91-23-4. Essentially, I want to use a regex pattern matcher on the potential ISBN to see if there is a valid 13 digit ISBN. How do I 'ignore' the "-" character so I can just regex for a \d{13} pattern? My function:
public String parseISBN (String sourceCode) {
int location = sourceCode.indexOf("ISBN") + 5;
String ISBN = sourceCode.substring(location); //substring after "ISBN" occurs
int i = 0;
while ( ISBN.charAt(i) != ' ' )
i++;
ISBN = ISBN.substring(0, i); //should contain potential ISBN value
Pattern pattern = Pattern.compile("\\d{13}"); //this clearly will find 13 consecutive numbers, but I need it to ignore the "-" character
Matcher matcher = pattern.matcher(ISBN);
if (matcher.find()) return ISBN;
else return null;
}

Alternative 1:
pattern.matcher(ISBN.replace("-", ""))
Alternative 2: Something like
Pattern.compile("(\\d-?){13}")
Demo of second alternative:
String ISBN = "ISBN: 123-456-789-112-3, ISBN: 1234567891123";
Pattern pattern = Pattern.compile("(\\d-?){13}");
Matcher matcher = pattern.matcher(ISBN);
while (matcher.find())
System.out.println(matcher.group());
Output:
123-456-789-112-3
1234567891123

Try this:
Pattern.compile("\\d(-?\\d){12}")

Use this pattern:
Pattern.compile("(?:\\d-?){13}")
and strip all dashes from the found isbn number

Do it in one step with a pattern recognizing everything, and optional dashes between digits. No need to fiddle with ISBN offset + substrings.
ISBN(\d(-?\d){12})
If you want the raw number, strip dashes from the first matched subgroup afterwards.
I am not a Java guy so I won't show you code.

If you're going to be calling the method a lot, the best thing you can do is not compile the Pattern inside it. Otherwise, each time you call the method you'll spend more time creating the regex than you will actually searching for it.
But after looking at your code again, I think you have a bigger problem, performance-wise. All that business of locating "ISBN" and then creating substrings to apply the regex to is completely unnecessary. Let the regex do that stuff; it's what they're for. The following regex finds the "ISBN" sentinel and the following thirteen digits, if they're there:
static final Pattern isbnPattern = Pattern.compile(
"\\bISBN[^A-Z0-9]*+(\\d(?:-*+\\d){12})", Pattern.CASE_INSENSITIVE );
The [^A-Z0-9]*+ gobbles up whatever characters may appear between the "ISBN" and the first digit. The possessive quantifier (*+) prevents needless backtracking; if the next character is not a digit, the regex engine immediately quits that match attempt and resumes scanning for another "ISBN" instance.
I used another possessive quantifier for the optional hyphens, plus a non-capturing group ((?:...)) for the repeated portion; that gives another slight performance gain over the capturing groups most of the other responders are using. But I used a capturing group for the whole number, so it can be extracted from the overall match easily. With these changes, your method reduces to this:
public String parseISBN (String source) {
Matcher m = isbnPattern.matcher(source);
return m.find() ? m.group(1) : null;
}
...and it's much more efficient, too. Note that we haven't addressed how the strings are getting into memory. If you're doing the I/O yourself, it's possible there are significant performance gains to be achieved in that area, too.

You can strip out the dashes with string manipulation, or you could use this:
"\\b(?:\\d-?){13}\\b"
It has the added bonus of making sure the string doesn't start or end with -.

Try stripping the dashes out, and regex the new string

you can try this
"(?:[0-9]{9}[0-9X]|[0-9]{13}|[0-9][0-9-]{11}[0-9X]|[0-9][0-9-]{15}[0-9])(?![0-9-])"

How do I parse recurring pattern with regex

I want to use regex to find unknown number of arguments in a string. I think that if I explain it would be hard so let's just see the example:
The regex: #ISNULL\('(.*?)','(.*?)','(.*?)'\)
The String: #ISNULL('1','2','3')
The result:
Group[0] "#ISNULL('1','2','3')" at 0 - 20
Group[1] "1" at 9 - 10
Group[2] "2" at 13 - 14
Group[3] "3" at 17 - 18
That's working great.
The problem begins when I need to find unknown number of arguments (2 and more).
What changes do I need to do to the regex in order to find all the arguments that will occur in the string?
So, if I parse this string "#ISNULL('1','2','3','4','5','6')" I'll find all the arguments.

If you don't know the number of potential matches in a repeated construct, you need a regex engine that supports captures in addition to capturing groups. Only .NET and Perl 6 offer this currently.
In C#:
string pattern = #"#ISNULL\(('([^']*)',?)+\)";
string input = #"#ISNULL('1','2','3','4','5','6')";
Match match = Regex.Match(input, pattern);
if (match.Success) {
Console.WriteLine("Matched text: {0}", match.Value);
for (int ctr = 1; ctr < match.Groups.Count; ctr++) {
Console.WriteLine(" Group {0}: {1}", ctr, match.Groups[ctr].Value);
int captureCtr = 0;
foreach (Capture capture in match.Groups[ctr].Captures) {
Console.WriteLine(" Capture {0}: {1}",
captureCtr, capture.Value);
captureCtr++;
}
}
}
In other regex flavors, you have to do it in two steps. E.g., in Java (code snippets courtesy of RegexBuddy):
First, find the part of the string you need:
Pattern regex = Pattern.compile("#ISNULL\\(('([^']*)',?)+\\)");
// or, using non-capturing groups:
// Pattern regex = Pattern.compile("#ISNULL\\((?:'(?:[^']*)',?)+\\)");
Matcher regexMatcher = regex.matcher(subjectString);
if (regexMatcher.find()) {
ResultString = regexMatcher.group();
}
Then use another regex to find and iterate over your matches:
List<String> matchList = new ArrayList<String>();
try {
Pattern regex = Pattern.compile("'([^']*)'");
Matcher regexMatcher = regex.matcher(ResultString);
while (regexMatcher.find()) {
matchList.add(regexMatcher.group(1));
}

This answer is somewhat speculative as i have no clue what regex engine you are using.
If the parameters are always numbers and always enclosed in single quotes, then why don't you try using the digit class like this:
'(\d)+?'
This is just the \d class and the extraneous #ISNULL stuff removed, as i assume you are only interested in the parameters themselves. You may not need the + and of course i don't know whether the engine you are using supports the lazy ? operator, just give it a go.