I thought I had some proficiency with regular expressions...until I met perl...

The goal was a substitution in which literal square brackets were to be part of the replacement text and in which certain variables would be used in the replacement as well. I had assumed that the brackets would be treated as literals. Wrong. Following are examples of the kinds of results I got:

$s = 'now is the time for all good etc.;'
$bef = 'before';  $mid = 'middle';  $aft = 'after';

Regexp:   result   (was it expected?)

s/.+/$bef$mid$aft/:  beforemiddleafter   (expected result,
   if no brackets)
s/.+/$bef[$mid$aft/:   (SYNTAX ERROR: "scalar found
   where operator expected"...)
s/.+/[$bef]$mid$aft/:  [before]middleafter    (expected)
s/.+/$bef[$mid]$aft/:  after                  (huh?)
s/.+/$bef$mid[$aft]/:  before                 (whaa?)

[download]

So much for proficiency. I had been aware that not every possible
sort of text is taken literally on the "replace-with" side of the substitution,
but I was unprepared for the above results. I need to do some more reading.
Which of the sundry books on perl would provide the best information about
what is happening in these kinds of substitutions?
T.I.A. . . .

In reply to Regexp: not what I'd expected by greenhorn

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