Regular Expressions 101

Group 1(\d+)

\d+a digit, repeated at least once

Non-Capturing Group(?:_)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Negative Lookahead(?![\s\S]*\1)

Character Class[\s\S]*

*matches any number of characters from the set below:

\sany whitespace character

\Sany non-whitespace character

\1the text saved by group 1

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

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

(\d+)(?:_)(?![\s\S]*\1)

New

http://images.1256_120*75 
http://images.123456_120*75
http://images.784217_120*75
http://images.784217_120*75
http://images.78317_120*75
http://images.784217_120*75
http://images.78217_120*75
http://images.12456_120*75 
http://images.12456_120*75
http://images.784217_120*75
http://images.784217_120*75
http://images.783217_120*75
http://images.784217_120*75
http://images.784217_120*75