Question 231886 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Regex for a string that cannot start with number but can be followed by alphabetic character

I am writing a regular expression which has multiple permutations and combinations. I did write the regex individually but how to combine them to make it a single regex. Please guide.

Allowed strings:

  • combination of alphabets and numbers
  • can have space in between
  • can have special characters at start, end and in between also (cannot have # + ,)
  • allowed examples for reference dfg, rt534, 34dfg, dfg(space)564(space)dfg545, !sdf7&*

Not allowed strings

  • cannot have space at start and end
  • cannot have # + , anywhere in the string
  • cannot start with number but can be followed by an alphabet
  • Ex: allowed – 445fsdf
  • Ex: not allowed – 4
  • not-allowed examples for reference 345, (space)sdfs, sdfsdf(space), #df8, sdfsdf(comma)4534

The individual regex I have are

^[A-Za-z0-9]*$
[^#+\,]
^[^s]+(s+[^s]+)*$

Please guide me in combining the regular expressions.

Tags:

3

Answers


  1. 0

    If you want to replicate logical AND with regex, there is a bigger answer, which I won’t attempt to replicate. Please read Regular Expressions: Is there an AND operator?

    However, if you want to replicate logical OR with regex you could use alternation like this:

    (patternA | patternB | patternC)

    e.g.

    (^[A-Za-z0-9]*$ | [^#+\,] | ^[^s]+(s+[^s]+)*$)

    A very concise summary of this operator (from the linked reference) is: "it tells the regex engine to match either everything to the left of the vertical bar, or everything to the right of the vertical bar."

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  2. 0

    You could use this regex, which combines the conditions that you state in the question:

    ^(?! )(?!.*s$)(?=.*[a-zA-Z])[^#+\,]+$

    It matches a string which:

    • (?! ) : doesn’t start with (space)
    • (?!.* $) : doesn’t end with (space)
    • (?=.*[a-zA-Z]) : contains at least one alphabetic character
    • [^#+\,]+ : consists only of characters not including #, +, or ,

    Regex demo on regex101. Note for the purposes of the demo I had to include n in the inverted character class to prevent matching text over line boundaries.

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  3. 0

    My understanding of the rule (long story short):

    • The string should not include any character of #+,.
    • The string should not start with a digit or a space character.
    • The string should not end with a space character.

    Then the corresponding regex will be:

    ^[^0-9#+\,s][^#+\,n]*[^#+\,s]$

    Demo

    Btw the shown example 34dfg should not be allowed as it starts with a digit.

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