Regular Expressions 101

Negative Lookbehind(?<![^\s\n])

Negated Character Class[^\s\n]

\sa Unicode whitespace character

\na line-feed (newline) character (ASCII 10)

\d{3}a Unicode decimal digit, repeated exactly 3 times

Character Class[./]

.the literal . (46₁₀ / 56₈ / 2E₁₆)

/the literal / (47₁₀ / 57₈ / 2F₁₆)

\d{3,6}a Unicode decimal digit, repeated between 3 and 6 times

Non-Capturing Group(?:/\d{3})?

?repeats the group contents below at most once:

/the literal / (47₁₀ / 57₈ / 2F₁₆)

\d{3}a Unicode decimal digit, repeated exactly 3 times

Negative Lookahead(?![^\s\n])

Negated Character Class[^\s\n]

\sa Unicode whitespace character

\na line-feed (newline) character (ASCII 10)

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

(?<![^\s\n])\d{3}[./]\d{3,6}(?:/\d{3})?(?![^\s\n])

Codes like 123/456
 
123/3456 
123/23456
 etc are correct

lorem\123/456