Thanks both---I didn't realise that $' was treated like that. Are all 'special variables' ($&, $N (N is integer)) expanded in that way too? So if you did something like: 
$temp =~ m/(\[0-9\])blah$1/;

[download]
would you match 
$temp = "[0-9]blah6";

[download]
rather than 
$temp = "[0-9]blah[0-9]";

[download]
?
V. interesting---I assumed that special characters inside the rest of the data would be ignored..
Cheers
<--edit to make the last sentence make more sense!-->
........
Those are my principles. If you don't like them I have others.
-- Groucho Marx
.......

In reply to Re^2: Regex error when [] occurs in file.. by why_bird
in thread Regex error when [] occurs in file.. by why_bird

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