Regex to match a digit two or four times

regex numbers
Renato Dinhani picture Renato Dinhani · Nov 18, 2011 · Viewed 86.2k times · Source

It's a simple question about regular expressions, but I'm not finding the answer.

I want to determine whether a number appears in sequence exactly two or four times. What syntax can I use?

\d{what goes here?}

I tried \d{2,4}, but this expression accepts three digits as well.

Answer

ruakh picture ruakh · Nov 18, 2011

There's no specific syntax for that, but there are lots of ways to do it:

(?:\d{4}|\d{2})    <-- alternation: four digits or two
\d{2}(?:\d{2})?    <-- two digits, and optionally two more
(?:\d{2}){1,2}     <-- two digits, times one or two

Related questions

How to extract numbers from a string in Python?

I would extract all the numbers contained in a string. Which is the better suited for the purpose, regular expressions or the isdigit() method? Example: line = "hello 12 hi 89" Result: [12, 89]

Read More
Extract a number from a string (JavaScript)

I have a string in JavaScript like #box2 and I just want the 2 from it. I tried: var thestring = $(this).attr('href'); var thenum = thestring.replace( /(^.+)(\w\d+\w)(.+$)/i,'$2'); alert(thenum); It still returns #box2 in the …

Read More
How do I include negative decimal numbers in this regular expression?

How do I match negative numbers as well by this regular expression? This regex works fine with positive values, but I want it to also allow negative values e.g. -10, -125.5 etc. ^[0-9]\d*(\.\d+)?$ Thanks

Read More