如何检查字符串中的最后一个字符？

Question

I have these line options:

• <40m:22s - ok

• <40m:22m; - not ok

• <40h:22s;<40m:22m - ok

• <40m:22m;<40m:22m; - not ok

I need to check for semicolons. If I have one entry, then it shouldn't be. If I have several entries in a row, then the last entry should not have a semicolon.

Now I have so far only succeeded:

([<>][1-9][0-9][hms]:[1-9][0-9][hms][;?]+)(?<!;)

I will be grateful for any help, hint

Answer 1

You can use

^(?:[<>][1-9][0-9]?[hms]:[1-9][0-9]?[hms](?:;(?!$)|$))+$

Or, a bit more verbose since it includes a repetition of the main pattern:

^[<>][1-9][0-9]?[hms]:[1-9][0-9]?[hms](?:;[<>][1-9][0-9]?[hms]:[1-9][0-9]?[hms])*$

See the regex #1 demo and regex #2 demo .

Details :

• ^ - start of string
• (?:[<>][1-9][0-9]?[hms]:[1-9][0-9]?[hms](?:;(?!$)|$))+ - one or more repetitions of
  • [<>] - a < or > char
  • [1-9] - a non-zero digit
  • [0-9]? - an optional digit (remove ? if it must be obligatory)
  • [hms] - h , m or s`
  • : - a colon
  • [1-9][0-9]?[hms] - a non-zero digit, an optional digit and h / m / s
  • (?:;(?!$)|$) - a ; not at the end of string or end of string
• $ - end of string.

The ^[<>][1-9][0-9]?[hms]:[1-9][0-9]?[hms](?:;[<>][1-9][0-9]?[hms]:[1-9][0-9]?[hms])*$ pattern follows the ^<MAIN>(?:<SEP><MAIN>)*$ scheme, and this pattern can be easily built dynamically using RegExp constructor.

 const texts = ['<40m:22s', '<40m:22m;', '<40h:22s;<40m:22m', '<40m:22m;<40m:22m;']; const rx = /^(?:[<>][1-9][0-9]?[hms]:[1-9][0-9]?[hms](?:;(?;$)|$))+$/. for (let text of texts) { console,log(text, '=>'. rx;test(text)); }

Answer 2

The general pattern for a delimited list is

^ item (delimiter item)* $

To avoid self-repetition and make it all more or less readable, it would make sense to use variables, template strings and whitespace. This way your regexp looks like a grammar definition (what it actually is) and not as a soup of symbols.

 let term = `[1-9] [0-9] [hms]` let item = `< ${term}: ${term}` let list = `^ ${item} (; ${item} )* $` let re = new RegExp(list.replace(/\s/g, '')) console.log(re) test = ` <40m:22s <40m:22m; <40h:22s;<40m:22m <40m:22m;<40m:22m; ` for (t of test.trim().split('\n')) console.log(t, re.test(t))

Answer 3

Lets simplify the problem to a = [<>][1-9][0-9][hms]:[1-9][0-9][hms] , so the accepted strings can be

a - ok
a;a - ok
a; - not ok
a;a; - not ok

so our regex must end with a which leads to a$ now we want to accept none or multiple a with ; between each a , the regex for that is (a;)*

combining these 2 will resut in const regex = /^(a;)*a$/;

now if we replace a with [<>][1-9][0-9][hms]:[1-9][0-9][hms] the result will be const regex = /^([<>][1-9][0-9][hms]:[1-9][0-9][hms];)*[<>][1-9][0-9][hms]:[1-9][0-9][hms]$/;

demo