Regex to check Optional Group of numbers

Question

i am trying to create a regex which should be able to accept the following strings

proj_asdasd_000.gz.xml
proj_asdasd.gz.xml

basically 2nd underscore is optional and if any value follows it, it should only be integer.

Following is my Regex that i am trying.

^proj([a-zA-z0-9]?)+_[a-zA-z]+(_[0-9]?)+\.[a-z]+.[a-z]

Any suggestion to make it accept the above mentioned strings?

Answer 1

You may use

^proj[a-zA-Z0-9]*_[a-zA-Z]+(?:_[0-9]+)?\.[a-z]+\.[a-z]+$
^proj[a-zA-Z0-9]*_[a-zA-Z]+(?:_[0-9]+)?(?:\.[a-z]+){2}$

See the regex demo

Details

• ^ - start of string
• proj - a literal substring
• [a-zA-Z0-9]* - 0 or more alphanumeric chars
• _ - a _ char
• [a-zA-Z]+ - 1+ ASCII letters
• (?:_[0-9]+)? - an optional sequence of an underscore followed with 1+ digits
• \.[a-z]+\.[a-z]+ = (?:\.[a-z]+){2} - two occurrences of . and 1+ lowercase ASCII letters
• $ - end of string.

Notes:

• [A-z] matches more than just ASCII letters
• ([a-zA-z0-9]?)+ matches an optional character 1 or more times, which makes little sense. Either match a char 1 or more times with + or 0 or more times with *, no need of parentheses
• (_[0-9]?)+ matches 1 or more sequences of _ followed by a single optional digit (so, it matches _9___1_, for example). The quantifiers must be swapped to match an optional sequence of _ and 1+ digits.