and assuming they're not always digits but a colon is always the separator, a combination of split, array slicing, and join: 

   $result = join( ':', (split( /:/, $string))[0..2]);

[download]

-derby

update: I like hdb's better ... less parens.

In reply to Re^2: Using the Substr by derby
in thread Using the Substr by Anonymous Monk

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