need a regular expresion to validate started double quote is ended or not

Question

Need a regular expression to validate a double quote(") is started and it must to be ended. Example : "This is valid" but "This is not valid

Answer 1

You could just count the numbers of quotes. If it's even it's OK

Answer 2

If count of unescaped " is even then the string is valid

Answer 3

Even number of quotes (") is valid.

For example in Python:

def isvalid(mystring):
    if mystring.count("\"")%2 == 0:
        return True
    return False

Answer 4

What language? Wouldn't it be easyer to just take out the first and last character and check if it is the "-char?

Like this (in php):

$first = substr($string, 0, 1);
$last = substr($string, -1);
if ($first == """ && $last == """) {}

For RegEx it would be something like:

/^\"(*.)\"$/

Answer 5

This pattern will work if no escaped doublequotes are allowed:

^"[^"]*"$

The ^ and $ are the beginning and end of the line anchors respectively.

The […] is a character class. Something like [aeiou] matches one of any of the lowercase vowels. [^…] is a negated character class. [^aeiou] matches one of anything but the lowercase vowels.

Thus the pattern validates that the entire line starts and ends with double quotes, and in between there are absolutely no doublequotes (but it could be empty).

See also

• regular-expressions.info/Anchors, Repetition
  • Examples/Programming constructs/Strings - Has patterns for various strings