Invalid Xpath - not equals to X amount of characters -

i trying xpath match variable1 = "text" , variable2 not equals 'ab' in first 2 characters , not equals 23 characters

what have not seem valid xpath:

/file[variable1='text'] , [variable2[substring(.,1,2) != ‘ab’]] , [variable2[substring!=(23)]]

please help!

as mentioned in comment, can use string-length() number of characters in variable :

/book[variable1='text']      [variable2[substring(.,1.2)!='ab' , string-length()!=24]]

alternatively, can use not(starts-with()) replace substring()!='xxx' :

/book[variable1='text']      [variable2[not(starts-with(.,'ab')) , string-length()!=24]]

MOno