Regular Expressions 101

Pro

1st Alternative^.*(.).*\1.*$(*SKIP)(*F)

^start of line

.*any character (except for line terminators), repeated any number of times

Group 1(.)

.any character (except for line terminators)

.*any character (except for line terminators), repeated any number of times

\1the text saved by group 1

.*any character (except for line terminators), repeated any number of times

$end of line

(*SKIP)acts like (*PRUNE), but the next unanchored match attempt starts where (*SKIP) was reached instead of at the next subject character

(*F)forces the current match attempt to fail at this position

2nd Alternative^[abcd]+$

^start of line

Character Class[abcd]+

+matches at least one character from the set below:

athe literal a (97₁₀ / 141₈ / 61₁₆) (case sensitive)

bthe literal b (98₁₀ / 142₈ / 62₁₆) (case sensitive)

cthe literal c (99₁₀ / 143₈ / 63₁₆) (case sensitive)

dthe literal d (100₁₀ / 144₈ / 64₁₆) (case sensitive)

$end of line

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

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25 tokens

^.*(.).*\1.*$(*SKIP)(*F)|^[abcd]+$

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