Regex to match only uppercase words with some exceptions

Question

I have technical strings as the following    The thing P1 must connect to the J236 thing in the Foo position     I would like to match with a regular expression those only-in-uppercase words  namely here P1 and J236   The problem is that I don t want to match the first letter of the sentence when it is a one-letter word   Example  in    A thing P1 must connect         I want P1 only  not A and P1  By doing that  I know that I can miss a real  word   like in  X must connect to Y   but I can live with it    Additionally  I don t want to match uppercase words if the sentence is all uppercase   Example    THING P1 MUST CONNECT TO X2     Of course  ideally  I would like to match the technical words P1 and X2 here but since they are  hidden  in the all-uppercase sentence and since these technical words have no specific pattern  it s impossible  Again I can live with it because all-uppercase sentences are not so frequent in my files   Thanks

User · Answer

Why do you need to do this in one monster-regex? You can use actual code to implement some of these rules, and doing so would be much easier to modify if those requirements change later.

For example:

if(/^[A-Z0-9\s]*$/)
    # sentence is all uppercase, so just fail out
    return 0;

# Carry on with matching uppercase terms

User · Answer

Maybe you can run this regex first to see if the line is all caps      A-Z  d W      That will match only if it s a line like THING P1 MUST CONNECT TO X2   Otherwise  you should be able to pull out the individual uppercase phrases with this     A-Z  A-Z d     That should match  P1  and  J236  in The thing P1 must connect to the J236 thing in the Foo position

User · Answer

I m not a regex guru by any means  But try    lt  A-Z0-9  A-Z0-9   gt    lt            start of word  A-Z0-9     one character  A-Z0-9     and one or more of them  gt            end of word   I won t try for the bonus points of the whole upper case sentence  hehe

User · Answer

Don t do things like  A-Z  or  0-9   Do  p Lu  and  d instead  Of course  this is valid for perl based regex flavours  This includes java   I would suggest that you don t make some huge regex  First split the text in sentences  then tokenize it  split into words   Use a regex to check each token word  Skip the first token from sentence  Check if all tokens are uppercase beforehand and skip the whole sentence if so  or alter the regex in this case

User · Answer

For the first case you propose you can use      blank     A-Z0-9     blank       for example   echo  The thing P1 must connect to the J236 thing in the Foo position    grep -oE     blank     A-Z0-9     blank       In the second case maybe you need to use something else and not a regex  maybe a script with a dictionary of technical words     Cheers  Fernando

User · Answer

To some extent  this is going to vary by the  flavour  of RegEx you re using  The following is based on  NET RegEx  which uses  b for word boundaries  In the last example  it also uses negative lookaround    lt    and      as well as non-capturing parentheses       Basically  though  if the terms always contain at least one uppercase letter followed by at least one number  you can use   b A-Z   0-9   b   For all-uppercase and numbers  total must be 2 or more     b A-Z0-9  2   b   For all-uppercase and numbers  but starting with at least one letter    b A-Z  A-Z0-9   b   The granddaddy  to return items that have any combination of uppercase letters and numbers  but which are not single letters at the beginning of a line and which are not part of a line that is all uppercase         lt     A-Z  b    lt    A-Z0-9     b A-Z0-9   b    A-Z0-9        breakdown   The regex starts with      The    signifies that -- although what follows is in parentheses  I m not interested in capturing the result  This is called  non-capturing parentheses   Here  I m using the paretheses because I m using alternation  see below    Inside the non-capturing parens  I have two separate clauses separated by the pipe symbol    This is alternation -- like an  or   The regex can match the first expression or the second  The two cases here are  is this the first word of the line  or  everything else   because we have the special requirement of excluding one-letter words at the beginning of the line   Now  let s look at each expression in the alternation   The first expression is     lt     A-Z  b  The main clause here is  A-Z  b  which is any one capital letter followed by a word boundary  which could be punctuation  whitespace  linebreak  etc  The part before that is    lt      which is a  negative lookbehind   This is a zero-width assertion  which means it doesn t  consume  characters as part of a match -- not really important to understand that here  The syntax for negative lookbehind in  NET is    lt  x   where x is the expression that must not exist before our main clause  Here that expression is simply    or start-of-line  so this side of the alternation translates as  any word consisting of a single  uppercase letter that is not at the beginning of the line    Okay  so we re matching one-letter  uppercase words that are not at the beginning of the line  We still need to match words consisting of all numbers and uppercase letters   That is handled by a relatively small portion of the second expression in the alternation   b A-Z0-9   b  The  bs represent word boundaries  and the  A-Z0-9   matches one or more numbers and capital letters together   The rest of the expression consists of other lookarounds     lt    A-Z0-9     is another negative lookbehind  where the expression is   A-Z0-9     This means what precedes must not be all capital letters and numbers   The second lookaround is     A-Z0-9      which is a negative lookahead  This means what follows must not be all capital letters and numbers   So  altogether  we are capturing words of all capital letters and numbers  and excluding one-letter  uppercase characters from the start of the line and everything from lines that are all uppercase   There is at least one weakness here in that the lookarounds in the second alternation expression act independently  so a sentence like  A P1 should connect to the J9  will match J9  but not P1  because everything before P1 is capitalized   It is possible to get around this issue  but it would almost triple the length of the regex  Trying to do so much in a single regex is seldom  if ever  justfied  You ll be better off breaking up the work either into multiple regexes or a combination of regex and standard string processing commands in your programming language of choice

[regex] Regex to match only uppercase "words" with some exceptions

Examples related to regex

Examples related to match

Examples related to uppercase