for example: 
$a = 'aa ab c c';
$a=~m/b/;

now

$` contains 'aa a'
$& contains 'b'
$' contains ' c c'

[download]
in other words all symbols of a line before the found result
found result,
and all the symbols after found results

In reply to Re^3: longest common substring (with needed tweaks) by Lennotoecom
in thread longest common substring (with needed tweaks) by R56

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