If you included -l on your shebang line as I have, it would add the newlines for you, but since many people do not like simple :), you can do this:

#! perl -sw
use strict;

m[
    (?:^[^0]*0[^0]*0[^0]*$)|
    (?:^[^1]*1[^1]*1[^1]*$)|
    (?:^[^2]*2[^2]*2[^2]*$)|
    (?:^[^3]*3[^3]*3[^3]*$)|
    (?:^[^4]*4[^4]*4[^4]*$)|
    (?:^[^5]*5[^5]*5[^5]*$)|
    (?:^[^6]*6[^6]*6[^6]*$)|
    (?:^[^7]*7[^7]*7[^7]*$)|
    (?:^[^8]*8[^8]*8[^8]*$)|
    (?:^[^9]*9[^9]*9[^9]*$)
]x and print "$_\n" for '0000' .. '9999';
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