Why do they use the “.” operator in Perl if it does not alter the string? 
I do not use Perl, but some reading (like here and here) seem to say that the . operator is a concatenation operator (much like + in Python, or .(the same symbol) in PHP). Concatenation joins two strings together, but, as string are immutable, a new string is created that is a combination of the strings you concatenated. I hope this helps!
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