Here's another thread which might help explain things: Regular expression "replace string interpolation" problem.

What confuses a lot of people is that when the replacement is a simple expression like $that, the following are equivalent: 

s/$this/$that/;
s/$this/$that/e;

[download]
However, note how this changes when the replacement varies just a little: 
# these are are equivalent:
s/$this/some text/;
s/$this/"some text"/e;

# and so are these:
s/$this/$that was close/;
s/$this/$that." was close"/e;

[download]

In reply to Re: /e in regexes by pc88mxer
in thread /e in regexes by waldner

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