Re^2: Regex error when [] occurs in file..

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/;
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would you match

$temp = "[0-9]blah6";
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rather than

$temp = "[0-9]blah[0-9]";
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?
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
.......

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Re^3: Regex error when [] occurs in file.. by Joost (Canon) on Mar 03, 2008 at 16:11 UTC
Are all 'special variables' ($&, $N (N is integer)) expanded in that way too? All variables are expanded that way, special or not: `my $var = '[ab]'; my $string = '12a3434'; print "match" if $string =~ /$var/;` [download] See also quotemeta and the \Q and \E escape sequences. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^3: Regex error when [] occurs in file.. ($1 vs. \1) by almut (Canon) on Mar 03, 2008 at 16:31 UTC
`$temp =~ m/(\[0-9\])blah$1/;` [download] I think you meant `$temp =~ m/(\[0-9\])blah\1/;` [download] in which case any special characters in the content of the backreference `\1` would not be treated special. IOW, `"[0-9]blah[0-9]"` would match, but not `"[0-9]blah6"`: `#!/usr/bin/perl use strict; use warnings; for my $temp ("[0-9]blah[0-9]", "[0-9]blah6") { printf "%-15s ", $temp; if ($temp =~ /(\[0-9\])blah\1/) { print "matched\n"; } else { print "didn't match\n"; } }` [download] prints `[0-9]blah[0-9] matched [0-9]blah6 didn't match` [download] while, if you replace `\1` with `$1` in the above regex, it prints `Use of uninitialized value in concatenation (.) or string at ./671663. +pl line 8. [0-9]blah[0-9] matched [0-9]blah6 matched` [download] This is because `$1` isn't defined here, thus the regex effectively becomes `/(\[0-9\])blah/`... Update: added demo code.	[reply] [d/l] [select]