How to limit regex optional characters to one of two values?
I am working up a regex that will match if the first character is 'S', 'U', or absent. I've gotten it to match the two characters just fine, but I can't figure out how to match the absent character. Here's what I have so far.
String a = 'S02-1234'; String b = 'T02-1234'; String c = 'U02-1234'; String d = '02-1234'; Pattern regex = Pattern.compile('([U|S])02-1234'); Matcher ma = regex.matcher(a); system.debug('S02-1234 ' + ma.matches()); Matcher mb = regex.matcher(b); system.debug('T02-1234 ' + mb.matches()); Matcher mc = regex.matcher(c); system.debug('U02-1234 ' + mc.matches()); Matcher md = regex.matcher(d); system.debug('02-1234 ' + md.matches());
String a match, GOOD!
String b does not match, GOOD!
String c matches, GOOD!
String d does not match, NOT good! :(
I've googled the question quite a bit, and suspect that I might not be using the right keyword. I'll bet it's something simple too... I just can't find it.
You're just missing the ?, which makes it optional (technically defined as 0 or 1 occurrences):
Pattern regex = Pattern.compile('([U|S])?02-1234');
Note that technically, using [], you don't want the | "operator", because you're actually checking if the string starts with U, S, or |. Similarly, you don't need the (), because it's not necessary here.
Pattern regex = Pattern.compile('[US]?02-1234'); [] is a "character class", which means "allow any one of the values in the bracket". You might want to read more about how regular expressions work; most people like to link to Regular Expressions to learn more about regex optional character and how to build proper regular expressions, and you can search on your favourite search engines for JavaScript-based sites that let you put in a pattern and a string to test.