RegExp matching string not starting with my

regex regex-negation pmd
Dominik Sandjaja picture Dominik Sandjaja · Jan 22, 2010 · Viewed 208.9k times · Source

For PMD I'd like to have a rule which warns me of those ugly variables which start with my.
This means I have to accept all variables which do NOT start with my.

So, I need a RegEx (re) which behaves as follows:

re.match('myVar')       == false
re.match('manager')     == true
re.match('thisIsMyVar') == true
re.match('myOtherVar')  == false
re.match('stuff')       == true

I've tried different ones but haven't got it working yet.

Answer

Tim Pietzcker picture Tim Pietzcker · Jan 22, 2010 
^(?!my)\w+$

should work.

It first ensures that it's not possible to match my at the start of the string, and then matches alphanumeric characters until the end of the string. Whitespace anywhere in the string will cause the regex to fail. Depending on your input you might want to either strip whitespace in the front and back of the string before passing it to the regex, or use add optional whitespace matchers to the regex like ^\s*(?!my)(\w+)\s*$. In this case, backreference 1 will contain the name of the variable.

And if you need to ensure that your variable name starts with a certain group of characters, say [A-Za-z_], use 

^(?!my)[A-Za-z_]\w*$

Note the change from + to *.

Related questions

Regular expression to match a line that doesn't contain a word

I know it's possible to match a word and then reverse the matches using other tools (e.g. grep -v). However, is it possible to match lines that do not contain a specific word, e.g. hede, using a regular …

Read More
Regex - Does not contain certain Characters

I need a regex to match if anywhere in a sentence there is NOT either < or >. If either < or > are in the string then it must return false. I had a partial success with this but …

Read More
RegEx to exclude a specific string constant

Can regular expression be utilized to match any string except a specific string constant let us say "ABC" ? Is this possible to exclude just one specific string constant? Thanks your help in advance.

Read More