Whitespaces and Regex expression

Question

I need to determine if a string contains Invalid chars. The criteria is that it should only have [a-z], [A-Z], [0-9] and [/,.-\] characters and anything else is invalid. Also, chars followed by space followed by / followed by space followed by chars is valid. The regex I have below takes care of the first criteria but I am struggling with the second. I have tried many combinations, something like these, but no success.

public bool ContainsInvalidChars(string s)
{
    return new Regex(@"[^a-zA-Z0-9/,.-][@"\s/\s"]).IsMatch(s);
}

Examples of input strings:

below is Valid
CSU,USD,6230.67,705RA0 / 2YKMP,5/11/2020,5/11/2020,VM

below is invalid
CSU,USD,6230.67,705RA0 /2YKMP,5/11/2020,5/11/2020,VM

below is invalid
CSU, USD,6230.67,705RA0 / 2YKMP,5/11/2020,5/11/2020,VM

Any help is greatly appreciated. Thanks.

Your method does not return any value. You should use return Regex.IsMatch(s, @"pattern_here");. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 14, 2020 at 13:29
Try return Regex.IsMatch(s, @"(?!\s/\s)(?<!\s/(?=\s))[^a-zA-Z0-9/,.-]"); — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 14, 2020 at 13:34
looks like X/Y for me. Imo use a well build CSV parser and trim the field. A space in front of a value should not be enough to make a line invalid. — Drag and Drop
– Drag and Drop, Commented May 14, 2020 at 13:34

The fourth bird · Accepted Answer · 2020-05-14 13:45:31Z

1

You might use the character class and repeat 0+ times in a group starting with space / space and again the character class.

^[a-zA-Z0-9/,.-]+(?: / [a-zA-Z0-9/,.-]+)*$

Regex demo | C# demo

The code could look like

public bool ContainsInvalidChars(string s)
{
    return new Regex(@"^[a-zA-Z0-9/,.-]+(?: / [a-zA-Z0-9/,.-]+)*$").IsMatch(s);
}

edited May 14, 2020 at 13:45

answered May 14, 2020 at 13:26

The fourth bird

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Comments

Dmitrii Bychenko · Accepted Answer · 2020-05-14 13:36:15Z

0

You have two types of valid chunks:

[a-zA-Z0-9/,.-]
\s/\s

let's make an arbitrary combination of them (note anchors ^ and $ - we want entire string match)

^(?:(?:\s/\s)*[a-zA-Z0-9/,.-]*)*$

Finally, invalid means not matched:

Code:

 public static bool ContainsInvalidChars(string s) =>
   !Regex.IsMatch(s, @"^(?:(?:\s/\s)*[a-zA-Z0-9/,.-]*)*$");

Demo:

string[] tests = new string[] {
  @"CSU,USD,6230.67,705RA0 / 2YKMP,5/11/2020,5/11/2020,VM",
  @"CSU,USD,6230.67,705RA0 /2YKMP,5/11/2020,5/11/2020,VM",
  @"CSU, USD,6230.67,705RA0 / 2YKMP,5/11/2020,5/11/2020,VM",
};

string report = string.Join(Environment.NewLine, tests
  .Select(test => $"{test,-60} :: {(ContainsInvalidChars(test) ? "Invalid" : "Valid")}"));   

Console.Write(report);

Outcome:

CSU,USD,6230.67,705RA0 / 2YKMP,5/11/2020,5/11/2020,VM        :: Valid
CSU,USD,6230.67,705RA0 /2YKMP,5/11/2020,5/11/2020,VM         :: Invalid
CSU, USD,6230.67,705RA0 / 2YKMP,5/11/2020,5/11/2020,VM       :: Invalid

answered May 14, 2020 at 13:36

Dmitrii Bychenko

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1 Comment

suhasghorp Over a year ago

Thanks everyone. Learned something new about Regex from your responses.

Wiktor Stribiżew · Accepted Answer · 2020-05-14 13:38:34Z

0

I suggest using

public bool ContainsInvalidChars(string s)
{
    return Regex.IsMatch(s, @"(?!\s/\s)(?<!\s/(?=\s))[^a-zA-Z0-9/,.-]");
}

See the regex demo

Regex details

(?!\s/\s) - a location not immediately followed with whitespace + / + whitespace
(?<!\s/(?=\s)) - a location not immediately preceded with whitespace + / and then followed with whitespace
[^a-zA-Z0-9/,.-] - any char but an ASCII letter, digit, /, ,, . or -.

The two lookarounds just exclude matching whitespaces (that are otherwise matched with [^a-zA-Z0-9/,.-]) that are in a WHITESPACE + / + WHITESPACE chunk.

answered May 14, 2020 at 13:38

Wiktor Stribiżew

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