I'm trying to write a regular expression in order to not allow double spaces anywhere in a string, and also force a single space before a MO or GO mandatory, with no space allowed at the beginning and at the end of the string.
Example 1 : It is 40 GO right
Example 2 : It is 40GO wrong
Example 3 : It is 40 GO wrong
Here's what I've done so far ^[^ ][a-zA-Z0-9 ,()]*[^;'][^ ]$, which prevents spaces at the beginning and at the end, and also the ";" character. This one works like a charm.
My issue is not allowing double spaces anywhere in the string, and also forcing spaces right before MO or GO characters.
After a few hours of research, I've tried these (starting from the previous RegExp I wrote):
To prevent the double spaces: ^[^ ][a-zA-Z0-9 ,()]*((?!.* {2}).+)[^;'][^ ]$
To force a single space before MO: ^[^ ][a-zA-Z0-9 ,()]*(?=\sMO)*[^;'][^ ]$
But neither of the last two actually work. I'd be thankful to anyone that helps me figure this out
The lookahead (?!.* {2} can be omitted, and instead start the match with a non whitespace character and end the match with a non whitespace character and use a single space in an optionally repeated group.
If the string can not contain a ' or ; then using [^;'][^ ]$ means that the second last character should not be any of those characters.
But you can omit that part, as the character class [a-zA-Z0-9,()] does not match ; and '
Note that using a character class like [^ ] and [^;'] actually expect a single character, making the pattern that you tried having a minimum length.
Instead, you can rule out the presence of GO or MO preceded by a non whitespace character.
^(?!.*\S[MG]O\b)[a-zA-Z0-9,()]+(?: [a-zA-Z0-9,()]+)*$
The pattern matches:
^ Start of string(?!.*\S[MG]O\b) Negative lookahead, assert not a non whitspace character followed by either MO or GO to the right. The word boundary \b prevents a partial word match[a-zA-Z0-9,()]+ Start the match with 1+ occurrences of any of the listed characters (Note that there is no space in it)(?: [a-zA-Z0-9,()]+)* Optionally repeat the same character class with a leading space$ End of string