匹配没有单括号的字符串

Question

I am working on regular expression based validation of some user input fields. The string that needs to be validated in given below

{{custName}} With Account Number {{accountnumber}} Your Balance Is {{message_abc.com}}

and the respective regular expression to check the string is given below

[{{[A-Za-z,_.}} ]*

which works absolutely fine for the above mentioned string, but what I want is: if the string is eg:

{custName} With Account Number {accountnumber} Your Balance Is {message_abc.com}

It would give an error.

Answer 1

This matches strings that don't have any single brace:

^(?:(?!(?<!{){(?!{))(?!(?<!})}(?!}))[{[A-Za-z,_.} ])*$

• (??(?<!{){(?!{)) : avoid to match openning brace without another before or after
• (??(?<!})}(?!})) : avoid to match closing brace without another before or after

Demo & explanation

Answer 2

You can match from {{...}} followed by the character class without the space and without the curly braces.

Then repeat that 0+ as a whole and match at least a single times the {{...}} part.

^(?:\{\{[A-Za-z,_.]*}}[A-Za-z,_. ]*)*\{\{[A-Za-z,_.]*}}$

• ^ Start of string
• (?: Non capture group
  • \{\{[A-Za-z,_.]*}} Match {{...}}}
  • [A-Za-z,_. ]* [A-Za-z,_. ]* Optionally repeat any of the listed chars in the character class
• )* Close the group and repeat 0+ times
• \{\{[A-Za-z,_.]*}} Match at least a single occurrence of {{...}}}
• $ End of string

Regex demo | Php demo

If there can also be content before and after:

^[A-Za-z,_. ]*(?:\{\{[A-Za-z,_.]*}}[A-Za-z,_. ]*)+[A-Za-z,_. ]*$

Regex demo