php - Regexp matching 3 consecutive capital letters -

i have following text :

74 avenue emile counor

bat b2 appt b104

i want replace line feed, if the following 3 letters not 3 capitals.

for example, previous example should become:

74 avenue emile counor bat b2 appt b104

but

74 avenue emile counor

bat b2 appt b104

should stay.

i have tried many solutions via regexp tools, impossible match want.

here have tried far

preg_replace("/\n([^a-z]{3})/", " $1", $str)

if want negate following lf, way use negative lookahead:

$str = preg_replace("/\n(?![a-z]{3})/", " ", $str);

note lookahead test , content doesn't appear in match result.

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