how does the following do that in one step?

It's a lookup table. 

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
 !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_

[download]

The tr/// pattern condenses the table into ranges.
The description you gave condenses the table into a math formula.

In reply to Re: Converting To Uuencoded Format by ikegami
in thread Converting To Uuencoded Format by vegasjoe

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