Check if a string contains only special characters and no letters within them using regular expressions

Question

Check if a string contains only special characters and no letters within them using regular expressions

My goal is to validate a string to ensure it contains letters only between two '#' symbols.

For example:

#one# + #two# - is considered a valid string

#one# two - is not valid

#one# + half + #two# - is also not a valid string (only #one# and #two# are valid sections)

The rule is that odd occurrences of '#' allow for entering letters, while even occurrences of '#' should close the space where letters can be written.

I have created a regex pattern that works for most cases, but I'm struggling with the last scenario.

Here is my current regex pattern:

/^[^a-zA-Z]*(#.+#)[^a-zA-Z]*$/g

I'm testing this pattern on the regex testing site

As a last resort, if regex is not sufficient, I may consider splitting the string on '#' and checking the remaining sections for letters in typescript.

Any thoughts on how to successfully validate this type of string? Thank you.

regex string typescript validation

Answer 1

Answer №1

One approach is to utilize an alternation to match the entire string, either not containing a character a-z, a newline, or a #, OR matching the pattern #[a-zA-Z]+# where only characters a-z can be present in between

^(?:[^a-zA-Z\r\n#]|#[a-zA-Z]+#)+$

^ Denotes the start of the string
(?: Represents a non-capturing group
- [^a-zA-Z#\r\n] Matches any character except those listed
- | Or
- #[a-zA-Z]+# Matches #, 1 or more characters a-zA-Z, and #
)+ Closes the non-capturing group (with the alternation) and repeats it 1 or more times to avoid matching an empty string
$ Indicates the end of the string

Check out the Regex demo here

To also match odd occurrences, you could modify the regex like this

[^a-zA-Z\r\n#]|#[a-zA-Z]+#(?:[a-zA-Z]+#)*)+$

See the Regex demo for this variation

Answer 2

One approach is to utilize an alternation to match the entire string, either not containing a character a-z, a newline, or a #, OR matching the pattern #[a-zA-Z]+# where only characters a-z can be present in between

^(?:[^a-zA-Z\r\n#]|#[a-zA-Z]+#)+$

^ Denotes the start of the string
(?: Represents a non-capturing group
- [^a-zA-Z#\r\n] Matches any character except those listed
- | Or
- #[a-zA-Z]+# Matches #, 1 or more characters a-zA-Z, and #
)+ Closes the non-capturing group (with the alternation) and repeats it 1 or more times to avoid matching an empty string
$ Indicates the end of the string

Check out the Regex demo here

To also match odd occurrences, you could modify the regex like this

[^a-zA-Z\r\n#]|#[a-zA-Z]+#(?:[a-zA-Z]+#)*)+$

See the Regex demo for this variation

Check if a string contains only special characters and no letters within them using regular expressions

Answer №1

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