正则表达式与模式匹配

Question

I want to match a string pattern like below.

abcd;abcd;sdfdf;sdfdf;sdsdf;

1. ';' should appear at most 5 times.(or less)
2. if 5th ';' is at the end no characters should be followed after that
3. between two ';' s any character could be there.
4. Number of characters between two ";" are 5.

I used following regex expression. But it doesn't give desired results.

(((.{0,5});){0,4}([^;]{0,5})){1}

Once the entire string is not matching it should be unmatched.

I'm not aware how to make the last character ';' or empty. So that is not included in the logic above I've provided.

To elaborate more Following patterns are allowed.

sdfsg;;;;;
sfdsf;sdfsd;sfsdf;;
;;;;

unmatching examples

sdfsdf;sdfsd;sdf;sdfd;sdf;sdf;sdf

I'd really appreciate if somebody could help. If you provide an solution please kindly give an explanation so it'll help to learn.

Answer 1

Try this regex

^(?:[^;]{0,5};){1,4}(?:[^;]{0,5};?)?$

Visual explain https://regexper.com/#^%28%3F%3A[^%3B]{0%2C5}%3B%29{1%2C4}%28%3F%3A[^%3B]{0%2C5}%3B%3F%29%3F%24

• With ^ we match start of Line
• (?:) is a non capturing group (like () but don't store result to a groups)
• With [^;] we match all char except ;
• {0,5} catch 0 to 5 non ; char
• ; at the end we have a final ;
• {1,4} we match the previous pattern pattern from 1 to 4 time inclusive
• ;? the last ; is optinal but we can't have another char after
• $ the end of line

Answer 2

This regex matches all those rules

^([^;]{0,5};){0,4}[^;]{0,5};?$

the ([^;]{0,5};) matches any set of letters or nothing before a semicolon and the semicolon itself, the {0,4} makes sure there aren't more than 4 semicolons before the last character, the [^;]{0,5} matches any character after the last semicolon, the ;? matches 1 or no semicolon as the very last character, and the $ makes sure there aren't any characters after the last semicolon.

Answer 3

You can try this regex:

(?:[^;]*;?){1,5}

It will capture anything between ; and upto 5 times.

See demo at Regex101