Regular Expressions 101

Explanation
Pro

Negative Lookbehind(?<!\.)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\ba Unicode word boundary

Group 1((?:(?:\w+(?:\[\d+\])*)\.){2}(?:\w+(?:\[\d+\])*))

Non-Capturing Group(?:(?:\w+(?:\[\d+\])*)\.){2}

{2}repeats the group contents below exactly 2 times:

Non-Capturing Group(?:\w+(?:\[\d+\])*)

\w+a Unicode word character, repeated at least once

Non-Capturing Group(?:\[\d+\])*

*repeats the group contents below any number of times:

\[the literal [ (91₁₀ / 133₈ / 5B₁₆)

\d+a Unicode decimal digit, repeated at least once

\]the literal ] (93₁₀ / 135₈ / 5D₁₆)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Non-Capturing Group(?:\w+(?:\[\d+\])*)

\w+a Unicode word character, repeated at least once

Non-Capturing Group(?:\[\d+\])*

*repeats the group contents below any number of times:

\[the literal [ (91₁₀ / 133₈ / 5B₁₆)

\d+a Unicode decimal digit, repeated at least once

\]the literal ] (93₁₀ / 135₈ / 5D₁₆)

Negative Lookahead(?![\w\.])

Character Class[\w\.]

\wa Unicode word character

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Global pattern flags

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

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

25 tokens

Regular Expression

(?<!\.)\b((?:(?:\w+(?:\[\d+\])*)\.){2}(?:\w+(?:\[\d+\])*))(?![\w\.])

New

too long: 
stuff aa[1].bb[2].cc.dd stuff

short: 
stuff aa[1].bb[2] stuff

Capture:
stuff aa[1].bb[2][3].cc stuff
stuff aa[1].bb[2][3].cc[1] stuff
stuff aa[1].bb[2][3].cc[2][12] stuff
stuff a.b.c stuff

Extraction

too long: 
stuff aa[1].bb[2].cc.dd stuff

short: 
stuff aa[1].bb[2] stuff

Capture:
stuff aa[1].bb[2][3].cc stuff
stuff aa[1].bb[2][3].cc[1] stuff
stuff aa[1].bb[2][3].cc[2][12] stuff
stuff a.b.c stuff