REGEX for single character and any non blank number

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I have been pounding my head trying to figure out a regex for the following scenario.

I need the following to be matched:

X11
X.25
X12.
X-21.25

I don't want this matched:
X

I have come close with 2 options but both have issues. The 1st expression listed below won't match the missing decimal point on the first test in my list. If I add a question mark to make the decimal optional it fixes my initial problem but then it matches the standalone X without a number which I don't want.

What I have tried:

([X]-?[0-9]*\.)[0-9]*

([X]-?[0-9]*\.?)[0-9]*

Posted 23-Sep-22 9:15am

theskiguy

Updated 23-Sep-22 13:24pm

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OriginalGriff · Accepted Answer · 2022-09-23T09:32:00

Try this:

^X-?((\d+)|(\d+\.\d*)|(\.\d+))$

^X-?
      Beginning of line or string
      X-, zero or one repetitions
  [1]: A numbered capture group. [(\d+)|(\d+\.\d*)|(\.\d+)]
      Select from 3 alternatives
          [2]: A numbered capture group. [\d+]
              Any digit, one or more repetitions
          [3]: A numbered capture group. [\d+\.\d*]
              \d+\.\d*
                  Any digit, one or more repetitions
                  Literal .
                  Any digit, any number of repetitions
          [4]: A numbered capture group. [\.\d+]
              \.\d+
                  Literal .
                  Any digit, one or more repetitions
  End of line or string

Patrice T · Accepted Answer · 2022-09-23T13:24:00

Quote:

([X]-?[0-9]*\.)[0-9]*

As many parts are optionnal, you need a RegEx a little more complicated.

[X]-?(\d+\.*[0-9]*|.[0-9]*)

Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
RegExr: Learn, Build, & Test RegEx[^]
Online regex tester and debugger: PHP, PCRE, Python, Golang and JavaScript[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx: Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]
This site also show the Regex in a nice graph but can't test what match the RegEx: Regexper[^]

REGEX for single character and any non blank number

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