regex101: PCRE (Legacy) Substitution Workspace

Group 1((?<!\p{L})(?=\d(?=(?:[- _]*\d){3,4}(?!\p{L})))|(?!^)\G)

1st Alternative(?<!\p{L})(?=\d(?=(?:[- _]*\d){3,4}(?!\p{L})))

Negative Lookbehind(?<!\p{L})

\p{L}any Unicode letter

Positive Lookahead(?=\d(?=(?:[- _]*\d){3,4}(?!\p{L})))

\da digit

Positive Lookahead(?=(?:[- _]*\d){3,4}(?!\p{L}))

Non-Capturing Group(?:[- _]*\d){3,4}

{3,4}repeats the group contents below between 3 and 4 times:

Character Class[- _]*

*matches any number of characters from the set below:

-the literal - (45₁₀ / 55₈ / 2D₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

\da digit

Negative Lookahead(?!\p{L})

\p{L}any Unicode letter

2nd Alternative(?!^)\G

Negative Lookahead(?!^)

^start of string

\Gstart of current search

Character Class[- _]?

?matches at most one character from the set below:

-the literal - (45₁₀ / 55₈ / 2D₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

\da digit

Negative Lookahead(?!\d*\p{L})

\d*a digit, repeated any number of times

\p{L}any Unicode letter

Global pattern flags

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

25 tokens

Regular Expression

((?<!\p{L})(?=\d(?=(?:[- _]*\d){3,4}(?!\p{L})))|(?!^)\G)[- _]?\d(?!\d*\p{L})

New

"0000" will become "****"
"any text 000 00 more texts" will become "any text ***** more texts"..notice that the space is removed
"any text 000 00 more texts 00" will become "any text ***** more texts 00"

"any text 000 00 more texts 00 00" will become "any text ***** more texts ****"

"any text 00-00 more texts 00_00" will become "any text **** more texts ****"

Extraction

"0000" will become "****"
"any text 000 00 more texts" will become "any text ***** more texts"..notice that the space is removed
"any text 000 00 more texts 00" will become "any text ***** more texts 00"

"any text 000 00 more texts 00 00" will become "any text ***** more texts ****"

"any text 00-00 more texts 00_00" will become "any text **** more texts ****"